Cleaning piston heads

[Smelly]

Hi Team.

Decided to have a look at my 1989 Johnson 110 HP - take head off and laugh at all the salt build up since 1989.

Yes, paint was still on the head bolts - i.e.not taken off..

Anyway, should I clean tops of the pistons while head is off?

If so, best recoommned method?

Thanks

[BaysideMarine]

A can of Power tune or Engine tuner (similar product put out by each manufacturer) is good for cleaning carbs, crankcases and pistons, ring lands etc etc

Don't forget to resurface the heads before fitting them back and of course new head gaskets.

Cheers

[Kerry]

1989! And about time too? Only about 7 years overdue!

Regards, Kerry.

Good evening BM :D

[BaysideMarine]

hi Kez

[Roughasguts]

Carby clean is pretty good at melting the carbon off aswell.
But lube the bore and turn the motor over after, if you don't you will get surface rust in a fairly short time, not a good thing.

[Smelly]

Hi guys.

I bought this rig back in Jan this year and has been in storage for last 10 months.

This is why it has not attended to it yet..

Question - the pistons are not actually out - I have just taken head off for it's clean...

Do i need totake out pistons for clean?

Can i not just clean tops whilst they sit in there?

Hints of how to move (crank) the pistons?

Smelly

[Smelly]

How do I re-surface the piston heads?

Is there a spec?

What do I use?

[Smelly]

what do i bore the cylinder with?

[blaze]

all jobs for a pro smelly
cheers
blaze

[Roughasguts]

Smelly, if your not taking the pistons out you can't bore the cylinder, But I think you mean hone, that is take the polish of the bore. But no point doing that unless you put in new rings. So dont worry about the hone unless you see some deep scratches in the bore.

There be a nut at the top of the fly wheel, what the starter motor engages too. Stick a spanner on that that will turn the motor over.

Yeah you can clean the tops of the pistons just sittin there. Is there a carbon ridge at the very top of the bore? that be the carbon you really need to remove that lip. Otherwise the rings have no where to go there hitting a dead stop, that must be removed.

[Smelly]

What instrument do I use to clean carbon off piston heads?

Sorry, I did not mean to say 'bore' - I meant 'lube'. :o

What do I lube the cylinder with?

[Roughasguts]

Two stroke oil is good, bit of a smear of that and run the piston up and down by turning the fly wheel with a spanner.

Have fun.

[Smelly]

What instrument do I use to clean carbon off piston heads?

[finga64]

1989! And about time too? Only about 7 years overdue!

Regards, Kerry.

Good evening BM #:D

Why's that Kerry??

[BaysideMarine]

Smelly,

The Power tune makes the carbon come away from the piston crowns. Also a wire brush is good for stubborn carbon.

To resurface the heads you need a nice flat surface such as a thick piece of glass or a flat thich piece of timber. Tape a sheet of emery cloth on it and work the heads back and forth till its polished clean all the way around.

Some people get outboard heads machined but you are asking for trouble ding that. Machine shops can get it wrong and will generally take too much off which is why the emery cloth is the best.

Also, with the heads off you will be able to crank the engine over with your hand on the flywheel quite easily.

Cheers

[Roughasguts]

Carby clean should just melt it off, but a small scraper like a putty knife will help move the bulk of it off, if theres any left.

But scrape it, don't use the corner and scratch it off that may leave little grooves.

[Smelly]

thnaks

[Roughasguts]

Let us know how you get on. Pictures would be good before and after.

[yakka]

if you take your head to an engine reconditioner they can do the head and you will be assured of a flat finish. the work can be easily done with out taking to much off as when the head is milled the increments are in thousandths of an inch. did this as an appprentice (motor vehicles) many moons ago.

as was already said do not have too much taken off as this can raise the compression ratio (if there is a combustion chamber in the head) which might sound good and give better performance but it puts extra strain on the big end bearings of the con rod that are probably old and tired and these bearings will then 8-)fail.

[Smelly]

Thanks Yakka.

You are correct.

I don't really have time or $$ to take my whole head and take to a Pro - would be nice.

Maybe in 7 more years... 8-)

[Smelly]

Guts.

Unfortunately no pics.

But you should have seen the salt build up - CRIKEY!

It woudl have been good to take pics ofthis but too keen to get it clean - looked like hell had frozen over... 8-)

I just want people to know that I woudl never let a motor get to this stage..

People in this forum know very well I am very particular and keen.

I tell you what though - I am glad I did nottake this to a dealer.

It is taking forever.!

SO far 8 hours from beginning of first nut undone to one head being put back on with new gaskets. etc.. :o

Now - for the other head... :D

[Roughasguts]

Sounds great smelly, nothing like doing it your self, have a few tinnies makes it more fun.

Carby clean work okay for the carbon build up.

[BaysideMarine]

if you take your head to an engine reconditioner they can do the head and you will be assured of a flat finish. the work can be easily done with out taking to much off as when the head is milled the increments are in thousandths of an inch. did this as an appprentice (motor vehicles) many moons ago.

as was already said do not have too much taken off as this can raise the compression ratio (if there is a combustion chamber in the head) which might sound good and give better performance but it puts extra strain on the big end bearings of the con rod that are probably old and tired and these bearings will then #8-)fail.


You are correct in essence, but outboard mechanics do not typically utilise machine shops for head surfacing.

[blaze]

if you take your head to an engine reconditioner they can do the head and you will be assured of a flat finish. the work can be easily done with out taking to much off as when the head is milled the increments are in thousandths of an inch. did this as an appprentice (motor vehicles) many moons ago.

as was already said do not have too much taken off as this can raise the compression ratio (if there is a combustion chamber in the head) which might sound good and give better performance but it puts extra strain on the big end bearings of the con rod that are probably old and tired and these bearings will then #8-)fail.


You are correct in essence, but outboard mechanics do not typically utilise machine shops for head surfacing.



Not quite understanding you BM, if a head is "resurfaced" it needs to be machined, never seen an outboard repair shop with head resurfacing machines, so if they dont have a machine and dont take it to any one, its not called a resurface, it can only be claimed to have the old gasket removed and cleaned
cheers
blaze

[BaysideMarine]

Outboard mechanics do not typically resurface heads via a machine shop.

It is done (as prior stated) with the use of a large, thick plate of glass, or a thick flat piece of timber.

Emery cloth taped to it and work the head back and forth till all areas are bright and shiny.

Thats head resurfacing for outboards.

Machine shops are generally a no go for outboard head resurfacing but of course are utilised for block maching etc

[blaze]

Hi Nick
I know the system well having been in the trade for a number of years, If someone was quoting me a resurfacing of a head on an invoice and I ever found out it had been done like that I would be livid, not saying it may not be ample to clean up an "old 2 stroke" thats all it is, its not a resurface. Just hope they dont carry that practice over to the newer technolies with there much finer tolerence.
cheers
blaze

[Roughasguts]

So how do you guy's go about the wet and dry clean up of the head surface.

What grade paper ? and what motion, figure 8 pattern, or up and down, or circular.

I like a 800-1000 grit with a figure 8 patern.

[BaysideMarine]

Blaze, no other mechanics I know charge for head resurfacing. Its just a part of reassembly...

[BaysideMarine]

Roughasguts,

I use a sheet of 120 grit emery (so its dry paper) and any motion as long as the end result is a flat head.

Cheers

[BaysideMarine]

Yakka,

Hardened needle roller bearings do not get "old and tired" as you suggested.

Automotive mechanicals has some major differences to marine mechanicals.

Cheers

[Roughasguts]

120 grit !!! no wonder it takes me so long.

[BaysideMarine]

Too right mate...!! I #laughed hard when I read your 800-1000 grit!!

I hate the time it takes (about 3 minutes - feels like 20) with some blunt 120.... Its damn hard work....

Plus the taste of aluminium in your mouth for the rest of the night.....

Cheers

[Roughasguts]

You don't use light oil on the paper, you won't taste the aluminium then.
Less work on the arms too.

[BaysideMarine]

Nope I do it dry. Give the cloth the occasional blast to clean off the ally.

[Roughasguts]

Hmmmm might give it a try one day, I always thought a oil stone worked better with lube. So figured the emery paper stuff would be the same better wet.

[Smelly]

HI Guts.

Finished.

It felt good doing the whoel thing myself - saving heaps of doe and learning at same time...

Will let u know how it runs. THansk for your guidance.. ;)

[Roughasguts]

Good luck smelly, sure it will be fine.
Cheers

[yakka]

hi BM
just read your post about the bearings and as with anything they will wear out hardened steel or not and increasing the compression on old bearings will lead to much earlier failure.
especially when you need them the most like putting the juice on suddenly on a bar cossing!!!
8-)

[BaysideMarine]

Yakka,

You are not a marine mechanic are you....

If you are an auto mechanic please limit your comments to your field of experience. You deal with white metal bearings, soft cranks and things completely unrelated to the marine trade.

Needle roller bearings "essentially" do not wear out. A needle roller bearing assemblies only real enemy is water, as water will destroy the bearings and the bearing surfaces on the crank and rod surfaces.

A marine engine rebuild realistically does not typically require the replacement of bearings because these bearings do not wear. This of course is measured and high power magnified at time of rebuild.

Auto mechanical theology really cannot be aplied to marine mechanical theology.

Cheers

[Smelly]

Amen

[blaze]

may I suggest a needle roller bearing will wear out, they are not only used in the marine trade/engine, they be in near every gearbox on the road, just cause they are hard, dont mean they wont wear. And bugger me dont they run on unfiltered air.
cheers
blaze

[Smelly]

BM - keen for your response to this one... 8-)

[yakka]

hi bm
so an engine rebuild where bearings arn't replaced and the head is sandpapered flat.
should let people know where you work!
johnson don't think their bearings are magic. are available as spares. but what would they know!!! 8-)

[FNQCairns]

Yeah they wear, they have a friction a co-efficient that can be measured, if they didn't they wouldn't produce heat or drag either, one day possibly?

They are extremely efficient though, needing very minimal lubrication and can spin great RPM's with relativly small losses compared to shell bearings - largely because of the very thin oil film needed, low volume and contact area at any one time.

Also contrary to urban legend you cannot hurt these suckers by running the engine out of fuel at any rpm on any stock engine either.

Although rugged, extra loading ie Lugging or increases in compression will shorten their life, impossible not to but on an old unknow history motor - suck it and see.

But doing the time honoured sandpaper on glass re-face is not going to add any extra compression to speak about, now if it were shaved that can be a different story -depending.

cheers fnq

[BaysideMarine]

Blaze,

Outboards run on unfiltered air as there is not a great deal of dust out on the water........... If you disagree take it up with the people who build these things...

Yakka,

If you are not a marine mechanic then its best you refrain from leading people astray. For all others, ring around a few mechanics, folks. Better still how bout I give you a name and number for a former Merc National Service Manager from way back??? Noel Aarons, 0405 190 923. Talk to him about resurfacing outboard heads.. Talk to him about needle roller bearings....

With all due respect, please do not bother trying to have a go at me if you are not a marine mechanic yourself. Apart form being extremely arrogant its rather stupid as well....

And your absolute uneducated RUBBISH about Johnson (or any other manufacturer really) having their engine bearings available as spares.... WHY WOULDN'T THEY????? Um..... if an engine sucks in water its going to need new bearings... Ignition keys are spare parts items too, along with engine covers, midsections and numerous other items that may never need replacing.

I tell you what folks, heres where forums have big problems when clowns like Yakka can post the response that he posted above and it goes unchecked. What we have is someone who is not a marine mechanic having a go at someone who IS and is posting messages that INSINUATE or ALLEGE that the practices of my trade or myself (in line with normal trade practices) are not simply wrong but DODGY?????

Whats next??? Every engine needs new rod bolts (some do)???? or new head bolts with a rebuild?? Or every piston needs replacing and not just using 1 oversized slug??????

Bloody hell....

[Roughasguts]

Think the fella's are just having fun with you BM, can always count on you biting back.

[BaysideMarine]

Perhaps I should start throwing it back the other way and see what gives eh??

You may well be right RAG, but I don't see the funny side.... :(

[Smelly]

Merry XMAS :)

[blaze]

Hi BM
I dont get on chat boards to have a go at any one but I have been in the mechanical Game long enough to know that if a statement like needle rollers dont wear out then I should have the right to question that statement. I have been in the the trade 30 + years and have post trade qualifacations (not that that should have any thing to do with it). I agree that an uncontaminated needle roller will run for a long time but they will still wear out.
Funny about the unfiltered air though, if the motor is running out on the water the air is nice and clean but what about when flushing outboards, most people dont even think about there $20,000 motor running without filtering the air.
cheers
blaze

[finga64]

Funny about the unfiltered air though, if the motor is running out on the water the air is nice and clean but what about when flushing outboards, most people dont even think about there $20,000 motor running without filtering the air.
cheers
blaze
I thought it's a bit weird not having an air filter on the little Honda. Dust and crap gets in everywhere when I'm towing the boat around the country side and I worry about the salt spray getting in on bad days so i put a little pod filter on. The little Honda isn't anywhere near the $20,000 (I reckon you can get nearly 15 little Hondas for that :D) but it makes me feel better after 100km on a dirt road and I can start the little motor and feel confident no crap is getting in.
I should put some on the T.O.P. as well to stop the cockroaches getting in #>:(
My grandad taught me the sandpaper trick for the motor-bikes and such.
We use a 1/2" thick sheet of glass though (don't like the wood idea as wood isn't perfectly true) and 240 then 320 wet & dry paper and kero as lub. If I didn't do a figure eight he'd kick me up the bum for being a dill and stuffing it up. Just the same as sharpening chisels.
That gets the alloy heads really flat and true.
;D

[BaysideMarine]

Blaze,

Most of what I wrote there was really directed to Yakka

Cheers

[blaze]

cheers
;)

[yakka]

hi bm
just what bit that i wrote was incorrect. the bearings do wear as has been said by others and in great detail how this occurs.
this was on a motor that has a dubious history just going by the description of salt build up in the water jacket and is what 17 years old.
taking to much off the head increases the compressionand puts extra stress on the big ends. as again stated by others above.
these are principles that apply to all motors not just car or outboard.
shining the head how you suggested if doing it at home well fine, so be it.
being shiny does not guarantee a flat surface.
If its taken to engine reco they can shave the heag in 2 thousandths (or whatever the metri equivalent is) of an inch increments and ensure you have a truly flat head.

me thinketh you protest to much.
8-)

[BaysideMarine]

If you purchased a "remanufactured" outboard it would come with a complete set of new bearings and a price tag not far off purchasing a brand new powerhead.

Yakka, do you think that replacing one piston in an engine with an oversized piston is wrong??

Needle roller bearings are regarded typically as non wearing and are not required ot be replaced during a rebuild unless damaged by water or some other mechanical influence. Main bearings are almost never likely to be replaced although big ends require closer examination but in almost all cases will be returned to an engine.

Bear in mind the rollers are checked under high powered magnifier to check for any faults.

Salt build up occurs in any outboard engine that is used in salt water, and not a function of poor care or lack of maintenance. Flushing helps but it does not remove all the salt deposits. Some brands have finer water galleries than others and are more prone to clogging.

Even pressure on a head as its worked back and forth on emery cloth on a flat surface WILL ensure a flat surface. This is how it is done in the marine trade with alloy heads.

I do protest Yakka, yes loud and strong when people outside the industry tell someone within the industry that how the industry does things is wrong....

By the way, just a quick one for you, I assume you know what plastigauge is?

[finga64]

By the way, just a quick one for you, I assume you know what plastigauge is?

I do and I'm a sparky #;)
We used it a lot during my apprenticeship. Amasing stuff the old plastigauge and it's amasing how long it's been around.
In my opinion it's the only true way of checking the variablity of clearances between two supposed flat surfaces (does that make sense??)
;D

[Roughasguts]

Something more accurate than using me thumb print to measure thicknesses.

Might come in Handy.

[BaysideMarine]

Yes finga,

Thats about it mate.

Not used on outboards with roller bearings but very important for auto type engines (or some marine engines of course) with soft cranks and white metal bearings.

Gives you a guaranteed reading of your running clearances on your bearings.

Cheers,

Nicholas

[HarryO]

WOW!!!

Hi all.....

BM.... Please don't take offence, BUT, Are you a QUALIFIED mechanic?

Marine or otherwise?

(BTW, the 6 week tafe course in small engines doesn't count)

[BaysideMarine]

Wouldnt spend the time doing a 6 week tafe course harry. 6 weeks is not long enough to understand marine engines.

Its probably worth looking further into the term QUALIFIED. If you mean trade certificate, then NO.

So does that mean a succesful operation that repairs, services and rebuilds engines without a plaque on the wall is inadequate?

By the way, the bloke I mentioned a number of posts back, Noel Aarons, a former Mercury National Manager and Training School Lecturer for Mercury Australia and New Zealand (in the 60's) and subsequently has 40 years in the trade as a marine mechanic does not hold a formal qualification either....

Cheers

[Kerry]

http://www.cqnet.com.au/~user\aitken\gen\peeking.gif

[HarryO]

Hmmmm.....

Didn't think so...

I thought you were a bit hard on Yakka.

(Group Hug)

Thats all.. :)

[marshy]

As a qualified motor mechanic with 18 years experience including lots of engine & gearbox overhauling I would have to say that I agree wit BM.
2 stroke outboards are a whole different ball game to motor cars. I have rebuilt 1 outboard engine for myself & assisted with one other for a friend. These rebuilds were for pleasure ,not profit as outboard are not my field. In doing these rebuilds I learned a lot about the contruction & design of these motors. I purchased factory engine mauals for both engines & the manuals say quite clearly NOT to remove any more material from the heads than necessary & in fact describes the use of emery paper on a glass surface.They also say that in the normal course of an engine rebuild that The bearings do NOT need to be replaced unless they show signs of excessive wear from water incursion of lack of lubrication shown as
corrosion pits or dark discolouration on the crank journals . I know BM doesn't need anyone to defend him but I just thought I would put my 2cents worth in .

Merry Christmas
Marshy

[HarryO]

I agree with you, Marshy...

The two are similar, yet so diverse..

Cleaning the head surface on glass is a standard, but
if I caught one of my apprentices using 120 dry they would
get a very swift kick in the backside.

Start with 220 wet, finish with 400 wet. NOTHING ELSE.

BM, which engines don't have single use STT rod bolts?

[Roughasguts]

We gone and lost Smelly, where are you and what's happening, with that motor.

Got that bolt out yet? Try the tighten loosen bit with plenty of lube, you can even place your electric soldering iron on that bolt, then hit it with some good penetrant after you get it as hot as possible.

But if you snap the head off, Oh well join the club, bloody surprised you didn't snap one removing the heads.

Almost a waste of time those easy outs, But you have to start drilling the hole out anyway.
Start off nice and small after a center punch belt, or use a small die grinder stone to flatten out the stud that's left, the slightest angle on the broken stud will deflect the drill bit.

If the stud has broken below the thermostat housing great use that same size drill bit to be dead on center to use as your pilot hole.

Thing is you have to know when to stop drilling depth wise

"Nick any ideas how deep"
Maybe the same depth as the 2 other bolts you got out?????

Also you need to be 1.5 mm less in diameter than the original stud.
That be so you can run your tap in there and have a desent thread.

Run your tap in your Battery drill at a fairly slow speed, go in until it slows then run the thread out, and in again Use plenty of WD40 to clean out the thread as you go.

New drill bits mate, best quality as well, otherwise well you know.

[Roughasguts]

You know I was thinking about the 120 grit, this would leave a scratchy surface more so than me 800. "Maybe better"

So I think the 120 would be better for the gasket and whatever goo you use, so the gasket has the best adhesion, compared to a shiny surface.

Never had a problem with a creeping gasket before, but a rougher surface always gives better adhesion.

[lippa]

i agree with the trade certificate thing. i have no peice of paper, but i do own and operate my own spraypainting company. i just can't have an apprentice. but i can have plenty of "trainee's" go figure that one.


cheers

lippa

[FNQCairns]

Reading through the thread BM did say "effectively" in his original statement.

Love it when a group hug comes together ;D

[finga64]

Some of the best tradies I've ever seen and worked with haven't a ticket on the wall and some of the worst, clueless idiots have.
It's all about passion and committment to the job. What-ever it is. :-*

[BaysideMarine]

Harry,

Many engines pre around 1990 didn't use stretch bolts on the conrods.

The manual in all cases will indicate if a particular engine needs to have them replaced.

Many mechanics replace them as a matter of course, however it really isn't necessary. A close inspection with a magnifier for any minor cracks is sufficient to deem a bolt re-useable.

I was talking to a mate of mine recently (mechanic with a ticket on the wall) and I had just finished a 100hp Merc rebuild (1991). This has stretch bolts fitted. He had rebuilt one 6 months earlier and had re-used the stretch bolts...... oh dear... :(

80hrs on and the customers engine is still running fine. But he did agree with me that it might be best to strip it down quickly at its next service and toss in some new rod bolts........

So I guess when in doubt, replace the rod bolts. At about $5 a bolt it doesn't break the bank to change them.

RAG, goo on most headgaskets is not a good thing.

Lippa, yep thats the only thing that annoys me is the inability to have apprentices. Good cheap labour is hard to find... :)

And yes, where are you Smelly??

[Kerry]

So who does things the "accepted text book" no grease/goo on studs/bolts etc or who lightly greases gaskets and bolts etc :-?

Be honest now ;D

Regards, Kerry.

[finga64]

I'll go first Kerry.
I use some crap called Hylomar on head gaskets before assembly. Always.

Crap on the bolts depends where they go and what they do.
Conrod bolts etc ...didley squat (except if the book says something completely otherwise for some strange reason).
Head bolts; if going into water jacket some gasket goo (not normal gasket goo but some stuff Holden uses on their head bolts) around the thread to the head and some under the head of the bolt. I do this mainly to try and stop any corrosion of the bolts and to protect the thread a bit.
if not going into water jacket I simply follow the book procedure but usually bung a bit of the goo under the head so as to seal the bolt-head to whatever surface.
Come on. I'm bending over...shoot me down..... ;D

Good point though Kerry as a lot of people do different things just out of habit. Some are good practices and some are aren't (I'm been polite there ;))
Cheers Scott :-*

[Roughasguts]

I clean threads, blow them out, smear grease them as well.

Goo all me gasketts, never with copper based stuff, and most me head gaskets. To seal them against the minute amount of salt water,
Then prevailing salt build up which causes gasket failure.

If you look at a aircraft engine no oil leaks, if you find one it gets taken out of service.
Why no leaks sealer everywhere.

[dogsbody]

Where is Smelly?, this is better than any book ive read we've had good verses evil other people taking your eye of the plot, mystery, entrigue can't wait to see the ending. Roll credits ;D

Dave.

[yakka]

hi bm
only ever used micrometers and dial gauges when measuring things to do with the reco of an engine. we would reco the motor and dyno tune and test it. 12 L bus motors, d9, small single cylinder generator motors, side valve motors, bue print racing motors lots of motors.
got the manual out for my motor a 60 hp yamaha (I know, not a Johno)
it is a Clymer Shop manual 2-250 2 stroke 96-98, page 360 shows a picture of them hand surfacing a cylinder head. i read on and it is only done if head warpage is measured and less than .1 mm or 4 thousandths of an inch using 600 wet and dry on a surfacing plate. then machining is the alternative. never said not be careful as matter of fact said be careful.
reckon thick glass would do well , not ever convinced a piece of timber would.

now I know this is not a johnson but should be similar specs.

again for the yamaha page 318 good practice to replace needle bearings on rebuilds

when reconditioning motors we would not put an odd sized piston in. all the time and expense was in getting the motor out and striping it down and was a pointless exercise in saving what was a small amount of money when compared to the entire job.

I'm not saying it hasn't been done and done successfully but was not practiced where I worked.

I would not do this to a car I owned because of the way I learn't and I wold not do it to a boat motor taking me and the crew out to sea.
nothing said here will change my mind on that one.

this is from the world of motors outside of the marine. a head that is machined flat does not guarantee a proper seal with the head gasket when bolted back together if the finish on the head is rough. It might not seem much but depth of the finish if too deep was enough to allow a path of escape for the compressed fuel mix and lead to early failure of the head gasket. 120 grit would be in that class for these motors.

its beer time and enjoy reading the differing views all from differing perspectives.

8-) 8-)

[BaysideMarine]

Hmmmm.....

Didn't think so...

I thought you were a bit hard on Yakka.
(Group Hug)

Thats all.. #:)


Yeah, I agree...

I get quite passionate about my trade....

My unreserved apologies Yakka for having a dig.

Cheers,

Nicholas

[BaysideMarine]

Many head gaskets are self adhesive and adding a sealing compound (unless explicity indicated in the manual) is a very unwise idea and can lead to premature gasket failure. I never apply a sealer to a head gasket.

All head gaskets will leech salt out in a salt water environment. Thats normal and to be expected. Thats why they should be changed every 5 years (not that they ever are).

Rod bolts I usually use Loctite Stud Locker on them.

Head bolts go in dry along with all other integral powerhead bolts.

Crankcase halves are smeared with Loctite master gasket sealant.

Lower unit, waterpump housing and powerhead bolts get the treatment of nickel anti seize grease.

Cheers,

Nicholas

[BaysideMarine]

hi bm
only ever used micrometers and dial gauges when measuring things to do with the reco of an engine. we would reco the motor and dyno tune and test it. 12 L bus motors, d9, small single cylinder generator motors, side valve motors, bue print racing motors lots of motors.
got the manual out for my motor a 60 hp yamaha (I know, not a Johno)
it is a Clymer Shop manual (1)2-250 2 stroke 96-98, page 360 shows a picture of them hand surfacing a cylinder #head. i read on and it is only done if head warpage is measured and less than .1 mm or 4 thousandths of an inch using 600 wet and dry on a surfacing plate. then machining is the alternative. never said not be careful as matter of fact said be careful.
reckon thick glass would do well , not ever convinced a piece of timber would.

now I know this is not a johnson but should be similar specs.

again for the yamaha page 318 good practice to replace needle bearings on rebuilds (2)

when reconditioning motors we would not put an odd sized piston in. all the time and expense was in getting the motor out and striping it down and was a pointless exercise in saving what was a small amount of money when compared to the entire job.

I'm not saying it hasn't been done and done successfully but was not practiced where I worked.

I would not do this to a car I owned because of the way I learn't and I wold not do it to a boat motor taking me and the crew out to sea.
nothing said here will change my mind on that one. (3)

this is from the world of motors outside of the marine. a head that is machined flat does not guarantee a proper seal with the head gasket when bolted back together if the finish on the head is rough. It might not seem much but depth of the finish if too deep was enough to allow a path of escape for the compressed fuel mix and lead to early failure of the head gasket. 120 grit would be in that class for these motors. (4)

its beer time and enjoy reading the differing views all from differing perspectives.

8-) 8-)






Hi Yakka,

No agro, just putting a marine angle to your above post.

Hilight 1) Clymer or Seloc manuals are not well regarded in my trade as a suitable manual. They are a hybrid of a genuine workshop manual and things are often inaccurate and incomplete. A genuine workshop manual is important for marine engines. I don't know why it has worked out this way but the aftermarket manuals are so so different from the genuine. Perhaps its the same in the auto trade???? I dont know. Thats your area.

Hilight 2) I believe you will find that statement to be quite unique to your manual. If you ring Noel Aaorns (the former Merc National Service Manager) he will advise you that direct from Mercs engineers in the US that needle rollers do not require replacing for an engine rebuild and are only considered of no use when damaged by water (or perhaps excessive heat).

Hilight 3) Fitting an oversized piston is absolutely normal, common, everyday, routine (hope thats clear enough :) ) practice in the marine trade for 2 stroke engines. The replacement pistons are balanced in weight to the originals and there is no problem whatsoever. I understand this is not done in an automotive engine and fair enough, thats your trades thing. But in my game its definitely NORMAL and doesn't not harm an engine at all.

Hilight 4) Understand your point, but after reassembling many engines (checking comps at time of rebuild of course) and then servicing them 12 months later (and again rechecking comps) they show the same compression and no sign of water ingress to the cylinders or compression blow by into the water jackets (which usually will aerate the water around the head/s and cause overheat warnings).

Cheers,

Nicholas