conrod bolts keep snapping

[gazza2006au]

hey guys im in the process of rebuilding a mercury 4 stroke 25hp engine i keep snapping the original conrod bolts i bought one new bolt yesterday to replace the snapped bolt now another snapped one today the bolts are snapping at the top of the thread and they look to be the same length as the new bolt does anyone know why there snapping? there not even reaching 4.4 foot pounds before snapping and there ment to torque down to 12 foot pounds :o

[finga]

Go and buy a complete set of new ones.
I'd even get a set of new head bolts or studs and any other bolt that needs to be tensioned whilst I was at it.

A lot of bolts can only be tensioned once and once only.

[johncar]

Make sure that they are not bottoming out in the thread before they tighten and that they can screw in freely well past the thickness of the con rod cap pillar.
If that is Ok then I can only think that either the bolts are fatigued or your tension wrench is out of whack, the latter not likely I know..I have seen bolts before that the metal has broken down so badly I could almost snap them with my bare fingers but this is rare and no doubt a bad batch of bolts.

But yeah I agree probably good to replace them all in this case, but check thread depth anyway.

[cormorant]

Foot pounds , inch pounds??? ;)

Are you putting lubricant on threads and creating hydraulic lock in blind stud holes? Are you cleaning threads ?

Some new head bolts are tighten and use once and many now use tension plus 1/2 turn or such as well. As above they can not be reused but are usually clearly marked and noted in manuals. I wouldn't think they are used on a conrod of any motor- I've only seen em used on heads.

[Fed]

Could be your tension wrench is way out, does it feel like 4.4. foot pounds when they break?
You should be able to easily feel what 12lbs feels like on the end of a 1 foot wrench.
What does the wrench go up to, I wouldn't think a 200 Lb wrench would be all that accurate right at the very bottom end of the scale.

[gazza2006au]

thanks guys i will order some more bolts tomorrow the wrench starts at 10 foot pound however it does wind lower i tested it on my trailer wheel nuts and 13 foot pound does actually feel like it so i think the wrench is working also out of the 4 conrod bolts the only 1 bolt that actually torqued down was the new bolt while testing on the trailer wheel i set the wrench to 4.4 and 13 foot pounds it felt pretty much the same as the scale doesnt go down to 4.4 also i oiled the bolt threads as the manual says it doesnt say to oil the head of the bolt tho unlike head bolts?

what is this do the bolts up and give it half a turn method? ive never heard this how accurate is it?

[finga]

what is this do the bolts up and give it half a turn method? ive never heard this how accurate is it?
Usually take the bolt up to a certain torque and then go a further so many degrees.

http://www.youtube.com/watch?v=hz8vSFq3AHM&feature=player_detailpage#t=9s

[MackerelMan]

what is this do the bolts up and give it half a turn method? ive never heard this how accurate is it?

There are three methods to torque bolts,
1. Measuring bolt stretch, the most accurate method.
2. Torque wrench.
3. Angle of torque which specifies a turning moment once bolt head is seated. Whilst commonly used and specified I think it is widely accepted as not suitable for critical applications.

Stick with your torque wrench but as already mentioned use new bolts. Are you trying to torque to specs in one go or are you working up to torque.

[Spaniard_King]

what is this do the bolts up and give it half a turn method? ive never heard this how accurate is it?

There are three methods to torque bolts,
1. Measuring bolt stretch, the most accurate method.
2. Torque wrench.
3. Angle of torque which specifies a turning moment once bolt head is seated. Whilst commonly used and specified I think it is widely accepted as not suitable for critical applications.

Stick with your torque wrench but as already mentioned use new bolts. Are you trying to torque to specs in one go or are you working up to torque.

Sorry to say but Angle torque is the more accurate and prefered method in the Automotive industry today!

Something is seriously wrong if you are breaking bolts with 4.4lb of tension what are these bolts made of??? Plastic ?? Seriously look at the gear and method you are using. You dont want a failure before you start it

[FishHunter]

thanks guys i will order some more bolts tomorrow the wrench starts at 10 foot pound however it does wind lower i tested it on my trailer wheel nuts and 13 foot pound does actually feel like it so i think the wrench is working also out of the 4 conrod bolts the only 1 bolt that actually torqued down was the new bolt while testing on the trailer wheel i set the wrench to 4.4 and 13 foot pounds it felt pretty much the same as the scale doesnt go down to 4.4 also i oiled the bolt threads as the manual says it doesnt say to oil the head of the bolt tho unlike head bolts?

what is this do the bolts up and give it half a turn method? ive never heard this how accurate is it?

This is your problem. Use a torque wrench that starts lower than 4.4 ft lbs.

Of all the methods for tensioning bolts the bolt length method is the most accurate on non stretch bolts. Stretch bolts are another breed which were designed to overcome the problems associated with getting an accurate clamping force and to overcome the issues with people not knowing the correct way to torque bolts un calibrated torque wrenches and to do away with the need to retorque headbolts.

The bolts are torqued to a low setting and are then tightened into what is known as the plastic deformation zone these can only be used once and are commonly used on head and conrod bolts.

[Stuart]

If you have repeated the problam several times then it can only be one you or the torque wrench. Conrod bolts a pretty friggen strong so if your snapping them it would be tool or the person using the tool.

[gazza2006au]

just thought i would try torquing down the new bolt i had from yesterday that to snapped than i tried drilling it and totally $*@%#* the conrod :-? is there anyway of repairing this? im out of cash and screwed now im right at the start rebuilding the engine ive paid out a lot of $$$$ on new parts and fixing parts no one will buy my engine as it is... what to do now? a new conrod cost big $$$

[cormorant]

Gazza I can't work this out. Did you drill it and use a easyout or just drill it out ? Was it a blind hole before and you drilled straight through?

You really have to use a drill press and get holes for easyouts perfectlt centered and straight. A conrod bolt should come out easy as it has only tension on the bolt head and once it is snapped not nuch is required to unscrew the bolt

Gazza you are not a mechanic you are a butcher- said in jest but learning can be expensive but keep giving it a go. Cheaper sometimes to ask for advice or get someone who will do the unusual things for you.

[gazza2006au]

i drilled the bolts out twice before perfect this time the drill just went of center mercury wants $270 for a new rod im screwed bloke at the engine remanfacturer said he could try heicoil it but it might just pull the helicoil thru and his never done a helicoil on a conrod before

what should i do?

[MudRiverDan]

well I read this thread and it it very interesting.
I have limited knowledge but if your bolt pulls through while the engine is going, it will cause more than $250.00 worth of damage.

Will be good to see how you go, good luck.

cheers

[cormorant]

Off to the wreckers and geta new rod or buy overseas.

I wouldn't use a helicoil on a conrod.

How much meat is on that rod. Go up a size bolt?

[FishHunter]

Has nobody else picked up that he is attempting to use a Torque wrench below its minimum setting.

Gazza I strongly suggest you put the tools down untill you actually understand what you are trying to do and how to go about it or you will have a very expensive hand grenade.

[tunaticer]

I am questioning the tension setting of 4.4 ft/lbs??? is this setting correct?

Secondly, there is no way possible you will shear off a con rod bolt at 4.4 ft/lbs.

Get a decent torque wrench that reads correctly.

Post up a pic of your torque wrench please.

[Stuart]

You can try and tap a new thread but this would mean going up in size. If you do that I may also mean the bottom end is now out of balance. If you did re tap a thread for the next size bolt I would then go and get it the crank balanced.

Stu

[gazza2006au]

yeah i will get another conrod im looking at a second hand conrod from the USA its much cheaper than buying a new one over here $270 new vs USA $105 used plus delivery i called probably the biggest outboard wrecker in nsw and the bloke said they rarely see my engine come thru and didnt have a conrod my cousin tonight told me he recently done a head job on a car and snapped one of the bolts nice of him to lend me the torque wrench knowing this... also this torque wrench does go as little as 10 foot pounds but the conrod bolts need to be torqued to 4.4 foot pounds than retorqued to 13 foot pound so i should have been safe but i will buy a new torque wrench when i get some cash flow i can only get one from super cheap what one would u ideally get from these two?
my cousins torque wrench is a 1/2 inch full size i donno maybe 14-15 inch's long or longer bought from super cheap many years ago

http://www.supercheapauto.com.au/online-store/products/SCA-Torque-Wrench-3-8-Drive.aspx?pid=214304#Description
http://www.supercheapauto.com.au/online-store/products/SCA-Torque-Wrench-1-4-Drive.aspx?pid=214303#Description

[cormorant]

I use the old beam style wrench a warren brown and over 15 years everytime it has been matched against a calibrated one it has required no adjustment. The spring style ones do require adjusting. Release the spring tension after use so it will read accurately for longer.

Here is a cheap way to see if it is even close

http://www.youtube.com/watch?v=RUD81N_TlS8&feature=related

Gazza - good tools are a investment if you are going to keep doing mechanical stuff. You wouldn't believe the prices we used to pay for quality tools 25 years ago compared to how avaliable they are today. Buy very good quality cornerstone tools that you use regularly. Many of mine were bought from old guys retiring or upgrading.

There is a digital load cell that you can check torque wrenches against . They can also be used with a normal ratchet or bar as a TW. They were cheapish and pretty reliable . Look up ac delco digital torque.

[tunaticer]

I would be either getting that wrench assessed and calibrated or getting a mechanic mate to come and tension the bolts for you. I reckon your wrench is not reading correctly, probably not been released for a duration and that has affected the calibration. at 4.4 ft/lbs it is impossible to snap one of those bolts off.

[gazza2006au]

i remember my cousin saying a couple of weeks ago he bought his engine hoist and tools all at the same time 10 years ago i think he said also i remember using this same torque wrench 7 years ago when i replaced the cylinder head on a car in that times its probably been used a lot and been dropped by my cousins kids heaps of times over the years so investing in my own is what i should really do i also seen the digital TW adaptors but there like $85 thats a bit pricey do they stay accurate for longer or something? i also seen some other models on ebay kincrome and tengtools both a bit pricey for me at the moment but something i will consider spending that extra bit of money on

http://www.ebay.com.au/itm/Kincrome-Micrometer-Torque-Wrench-1-2-Square-Drive-/220610267237?pt=AU_Hand_Tools&hash=item335d658865

http://www.ebay.com.au/itm/TENG-TOOLS-MICROMETER-TORQUE-WRENCH-1-4-DRIVE-5-25-Nm-CALIBRATION-CERT-/290658940773?pt=AU_Car_Parts_Accessories&hash=item43ac9f7765

the TW im using is identical to this model http://www.ebay.com.au/itm/New-Professional-1-2-Drive-Adjustable-Torque-Wrench-Tool-Premium-Quality-Case-/290658958239?pt=AU_Sport_Cycling_Accessories&hash=item43ac9fbb9f

[thriller]

4.4 ft lb or 13ft lb torque would normally be achieved with 1/4 drive or 3/8 drive tools.
1/2 in drive is just silly for those poor bolts.

I can't speak on behalf of total cr@p tools but Torque wrench tools usually remain fairly close to calibration.


If I were you, I would get someone to assist you in your endeavour. goodluck

[The Woo]

^^^ He speaketh the truth.

[fishfeeder]

Just use a spanner and forget about the torque amounts... Do them up to there firm and then go a "LITTLE MORE" job done..... ::)
You must be pulling like a crazy man to continually be BRAKING bolts.... If its tight and your still pulling like a mad man you need to throw the tools out and buy a paddle, The chances are the motor wont go again anyway if your having so much trouble with conrod bolts...

There is a reason people do a course to become a mechanic !!

[cormorant]

Are you torquing in increments ?

I know it says 4 then 10 or whatever but that doesn't mean you do one bolt up to 4 then the other 3 as such.

When torquing anything down you do all of them gradually in the suggested pattern unless it says to do it in one final movement for the final torques.

As a rough guide I know from stuff I've done that a 8mm will have a torque of 200 inch lb but a waist or stepped down bolt will be half that approx at 130 inch lb.

Are you buying genuine bolts? not just bolt shop bolts? Are they the bolt for that exact model series motor and are you reading the exact model series manual? Did you check the numbers on the head of the bolt? Different model changes or generations of the same motors may have different components and different torque requirements.

Out of interest have you determined if they are "torque once" bolts and throw away or reuseable ones.


Gazza it is all a learing experience. Years ago on a european car before anyone ( but original factory mechanics) knew about torque once bolts and manuals weren't publically avaliable I saw quite a few expensive lessons learnt on very expensive cars and I won't even go into the subaru motors aftermarket head gaskets and people reusing torque once bolts again and wondering about 2nd and 3 failures.

I can see in the future that with a couple more generations of motors it will be unitary construction with fewer bolts and fancy welding ( quicker , lighter stronger with fancy metals, ceramic coatings) and motors ( or key parts) will be maintained and replaced not repaired as such due to it being cheaper in production and better for companies to stop non genuine parts if you know what I mean as only the big companies will have the manufacturing technology for a number of years. Sort of like why there is no non genuine computers for boat motors.

PS Have you asked the question on scream and fly or merc forums as blokes there do it every day and will have access to original factory documentation and advisorys , updates if there was a misprint etc.

PSS prices for parts seem expensive. ouch.

[gazza2006au]

Are you torquing in increments ?

I know it says 4 then 10 or whatever but that doesn't mean you do one bolt up to 4 then the other 3 as such.

When torquing anything down you do all of them gradually in the suggested pattern unless it says to do it in one final movement for the final torques.

As a rough guide I know from stuff I've done that a 8mm will have a torque of 200 inch lb but a waist or stepped down bolt will be half that approx at 130 inch lb.

Are you buying genuine bolts? not just bolt shop bolts? Are they the bolt for that exact model series motor and are you reading the exact model series manual? Did you check the numbers on the head of the bolt? Different model changes or generations of the same motors may have different components and different torque requirements.

Out of interest have you determined if they are "torque once" bolts and throw away or reuseable ones.


Gazza it is all a learing experience. Years ago on a european car before anyone ( but original factory mechanics) knew about torque once bolts and manuals weren't publically avaliable I saw quite a few expensive lessons learnt on very expensive cars and I won't even go into the subaru motors aftermarket head gaskets and people reusing torque once bolts again and wondering about 2nd and 3 failures.

I can see in the future that with a couple more generations of motors it will be unitary construction with fewer bolts and fancy welding ( quicker , lighter stronger with fancy metals, ceramic coatings) and motors ( or key parts) will be maintained and replaced not repaired as such due to it being cheaper in production and better for companies to stop non genuine parts if you know what I mean as only the big companies will have the manufacturing technology for a number of years. Sort of like why there is no non genuine computers for boat motors.

PS Have you asked the question on scream and fly or merc forums as blokes there do it every day and will have access to original factory documentation and advisorys , updates if there was a misprint etc.

PSS prices for parts seem expensive. ouch.

hey mate i will try to answer your questions

since the torque wrench handle twist lower than 10 foot pounds but doesnt have markings for less than 10 i used a normal wrench the last time and done up each bolt to what i thought would be ideal than torqued them down to 13 foot pounds

the manual doesnt say to torque the bolts in sequence it just says to torque them down

the first 2 bolts i snapped were the originals from the engine the 3rd bolt looked different but the bloke looked up the part number from my serial number i asked the sales guy he said thats the right bolt

the manual says inspect and measure bolts and reuse if within spec i have nothing to measure the stretch


You must be pulling like a crazy man to continually be BRAKING bolts.... If its tight and your still pulling like a mad man you need to throw the tools out and buy a paddle, The chances are the motor wont go again anyway if your having so much trouble with conrod bolts... thats a bit harsh mate i had faith in a faulty torque wrench am i to blame? probably i shouldnt have gone so far on doing up the bolts but at what point do u stop and think is this correct? u actually think no its correct because again the torque wrench didnt click so u keep going fair enough the two previous bolts snapped and i should have learn but i thought those bolts were only one time use bolts hence i just bought 4 new ones

[gazza2006au]

the TW i was using

[cormorant]

So you don't have a set of vernier calipers to measure the bolts you pulled out? Do they give exact specs for the length of bolts in the manual? Spare parts bloke could measure them for you or just buy new ones. I guess you have watched the video someone provided above and understand why bolts can only go to their torque setting and some can only do it once? People used to measure the Subaru head bolts as well and had a lot of failures. You could visibly see the stretch on them quite easily when compared to a new bolt set.


Dumb question - why did the bolts get undone in the first place? What was wrong with the motor?

[gazza2006au]

the engine had been sunk and im in the process of doing a complete rebuild

[The Woo]

That enormous torque wrench will be completely innacurate for small torque settings. Despite it's "calibration" beginning at 20ft/lb, it wouldn't be accurate there.

You need to step down to a 3/8 or 1/4 drive wrench. Where are you?

[MudRiverDan]

Those torque wrenches are nasty, they have a very rudimentary setting, to use one like that on a smaller bolt would possibly be way out of calibration.

If your going to do your own work I would definitely recommend buy something with a little more quality.

In years of late a lot of cheap tools have shown up on the market that claim to do the job, but doubt you would find one in any professionals toolbox.

Would have saved you $100 so far and a lot of time.

[gazza2006au]

ok im going to order the conrod on monday should take 3-5 days from the US can someone show me an ok but cheap torque wrench to buy online?

[Fed]

Measure a foot out on the bar and hook your fishing scales onto it, add some tape so it won't slip & pull your 12 Lbs.

[gazza2006au]

Measure a foot out on the bar and hook your fishing scales onto it, add some tape so it won't slip & pull your 12 Lbs. haha good idea but i dont have fishing scales lol

[finga]

I'd be looking for a 1/4 one and even then a lot do not go down that low (4.4ftlb) in their settings.
That's near the same as hanging a 2kg bag of spuds and 2 packs of Smiths crisps of a 300mm arm to get the same torque.

[gazza2006au]

I'd be looking for a 1/4 one and even then a lot do not go down that low (4.4ftlb) in their settings.your right i remember calling my local car auto shop the other day about a helicoil kit i was looking up there number and seen they now have a web site so i just done a check for a TW and they have two but both dont go down no where near 4.4ft/lb and abit pricey at over $100 how accurate are the super cheap auto TW's?

http://www.autoxcel.com.au/advanced_search_result.php?keywords=torque+wrench&x=25&y=14

[finga]

Have you tried the hire shop??

[gazza2006au]

Have you tried the hire shop??i just checked on the kennards hire web site they dont have any i found other sites but there TW start at 20 so i think im going to have to buy a 1/4 TW

[finga]

You could always use a stick of liquorice. The stuff from Woolies will start bending at about 4.4ftlb's
For the 12ftlb's use a musk stick

Just kidding ;)

[gazza2006au]

went to the second hand markets to see if i could find a used snap on torque wrench cheap half of the stores were already gone when i got there the other half packing up so i just went to super cheap auto and bought one of theres this one goes down to 4.5NM which is perfect altho a cheapie at only $63 i dont expect it to last long but comes with 12 months warranty

[gazza2006au]

ok guys now i can confirm my cousins torque wrench is screwed i had two bolts left i thought i would torque them down using the new wrench and guess what they torqued down perfectly no snapping bolts they torqued down to 6NM than 17NM but theres a catch.... my torque wrench only goes to 30NM and my head bolts need 47NM :-? i dont want to trust my cousins torque wrench on the head bolts so i guess i will have to go buy the 3/8" torque wrench bugger more money lol

[cgibbo308]

noooo gaz.. repack and take your one back to sc and say you got the wrong size and get it exchanged for the heavier tw :D

[gazza2006au]

noooo gaz.. repack and take your one back to sc and say you got the wrong size and get it exchanged for the heavier tw :DLOL sneaky... i would feel bad if i done that :( plus i need the 1/4" TW for next week when the conrod shows up i think the next model up 3/8" starts around 15NM so i wouldnt be able to use that one alone ive looked at the max torque setting for my engine it ranges i think it was around 150-165NM for the flywheel nut and counter balance piston nut so im thinking now i should just get the large TW i think that starts around 30NM and goes up to 200NM possibly 250NM which is the 1/2" model found some bargains on ebay a kincrome model 1/2" for $74 im waiting to see if the guy allows pickup's if not i will have to look somewhere else but the kincrome comes with a life time warranty

[finga]

Now Gazza....Listen to a word of wisdom and experience.
Buy the tools that fit your need (in this case 3 tension wrenches) and DON'T LEND YOUR TOOLS TO ANYONE!!!!!!

Otherwise you'll be in the same boat as your relative. You'll own a buggered tool.
I've found many people do not respect your tools as you would over the years and I have plenty of knackered tools to prove that theory.

I've also learnt not to borrow tools either because you normally have to fix them before you can use them.

So buy the exact tools you need and lock them up. Don't tell anyone you have them and they'll last forever.

[The Woo]

Also, with torque wrenches, never, EVER, EVER, use them to undo fasteners. They are for torquing right hand threads ONLY.

If you break that rule, you risk throwing the calibration out completely. It's by far the biggest reason torque wrenches become innaccurate.

[gazza2006au]

Now Gazza....Listen to a word of wisdom and experience.
Buy the tools that fit your need (in this case 3 tension wrenches) and DON'T LEND YOUR TOOLS TO ANYONE!!!!!!

Otherwise you'll be in the same boat as your relative. You'll own a buggered tool.
I've found many people do not respect your tools as you would over the years and I have plenty of knackered tools to prove that theory.

I've also learnt not to borrow tools either because you normally have to fix them before you can use them.

So buy the exact tools you need and lock them up. Don't tell anyone you have them and they'll last forever.haha i hear u loud and clear mate thanks ;D


Also, with torque wrenches, never, EVER, EVER, use them to undo fasteners. They are for torquing right hand threads ONLY.

If you break that rule, you risk throwing the calibration out completely. It's by far the biggest reason torque wrenches become innaccurate. yeah im yet to read the instructions i will do that today but i also read that online so thanks for the tip mate ;D

[gazza2006au]

ok guys the engine is mostly back together i had it running for around 5 seconds this morning i dont have the PTT hooked up yet and i ran it dry no water only to see if it would start the engine oil is full but i noticed there was a beeping noise coming from the engine howdo i know if the engine is pumping oil? or how do i know what sensor is triggering the alarm?

[Stuart]

Yould never start a outboard with out running water through it. You run the risk of burning out the rubber inpeller.

[Spaniard_King]

Yould never start a outboard with out running water through it. You run the risk of burning out the rubber inpeller.

Unless you have the gearbox off at the time :)

[gazza2006au]

hey guys heres a video of the engine running im waiting for a new oil pressure switch to show up at the mercury dealer also noticed a crack in the fuel pump plastic and mercury doesnt sell that part alone i have to buy a whole fuel pump big $$$ :o there $166 in the US i dont even wanna price one over her...

http://www.youtube.com/watch?v=igtBhp_mLFE