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Patrick Reese

Head Bolts keep loosening up

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After doing an extensive rebuild on our Commando 6 powered by the awesome Tecky HH60 (for all you Tecumseh naysayers).. I find that after the running it and letting it cool down that the headbolts have loosened up. I retorque them to 200 inch lbs and then the next day after my son takes it out for a ride around the property I check the tension and they've loosed up again. It seems I have a set of headbolts that no longer retain there tensile strength. The problem with this is the headbolts are no longer manufactured and they are an odd thread size.. 5/16" by 18 (thread) by 2" long with three of them being 2 1/4" long..

 

Apparently this is something to be ware of when rebuilding and older engine!

 

 

WH47_zpsbb702bd8.jpg

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Head bolts can loose their tensile strength properties over time and many heating cooling cycles.  I have successfully replaced mine with Socket Headed Cap Screws witch are grade 8 by definition on my Tecky H-60's.  I must admit that I usually do not get out the torque wrench for these small engines I think I have a fairly good feel for how tight they should be.  I also use die washers under the heads(hardened steel washers 1/8" thick)  this cuts down on the aluminum heads mushrooming out under the head of the bolt.  These motors run fairly low compression so the head bolts that are used are a bit over kill.  I actually have one motor that I used 316 SS bolts on the head which have a much lower yield strength then grade 8 bolts and it sealed up just fine.

 

And btw 5/16-18 UNC bolts are a standard size, and are probobly the second most common thread size behind 1/4-20, you should have no problem getting them almost anywhere.  I would recommend going to a real industrial fastener supply house such as Fastenal, their hardware is usually much better then the overpriced low grade junk sold at most hardware stores.  I specify fasteners as part of my job as an Engineering Technician and we buy them by the barrel in certain sizes, currently we only buy bolts in either HOLO-KROME or UNBRAKO brands as both are US made and have successfully proven themselves in the field over many years.  Most hardware store stuff is made overseas and you never know what you are buying or what steel was used to make them.

 

Sorry for the rant  :soapbox:

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I too just replace head bolts with Grade 8 cap bolts. I have not had an issue with them.

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It may not be the bolts, it may be the gasket squashing.  Up to a point you should need to do this only once, but on some gaskets it requires several times.

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IT was definately more than the gasket squashing down.. to date I had to retighten the original bolts 4 different times. Usually a proper torque-ing a heat up and cool down and then a re-torque is all that is needed.. but 4 times is way too much and they moved way too far with each re tightening..

Fastenal was a great tip. I just ran over there and they had what I needed. Grade 5 in gold cad! I torqued them down in steps in sequence to 200 inch lbs.. let the engine warm up for about 5 minutes and shut it down. I then rechecked the torque and with engine still warm they are still right where they were set. I'll go back and check them once it cools down.

 

Thanks!

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Wow, very interesting.  I have never heard of this on a small engine.  I did have a coleman air compressor popping head gaskets, and new studs fixed the problem.  Overall the quality was poor on the compressore head.

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Head bolts can loose their tensile strength properties over time and many heating cooling cycles.  I have successfully replaced mine with Socket Headed Cap Screws witch are grade 8 by definition on my Tecky H-60's.  I must admit that I usually do not get out the torque wrench for these small engines I think I have a fairly good feel for how tight they should be.  I also use die washers under the heads(hardened steel washers 1/8" thick)  this cuts down on the aluminum heads mushrooming out under the head of the bolt.  These motors run fairly low compression so the head bolts that are used are a bit over kill.  I actually have one motor that I used 316 SS bolts on the head which have a much lower yield strength then grade 8 bolts and it sealed up just fine.

 

And btw 5/16-18 UNC bolts are a standard size, and are probobly the second most common thread size behind 1/4-20, you should have no problem getting them almost anywhere.  I would recommend going to a real industrial fastener supply house such as Fastenal, their hardware is usually much better then the overpriced low grade junk sold at most hardware stores.  I specify fasteners as part of my job as an Engineering Technician and we buy them by the barrel in certain sizes, currently we only buy bolts in either HOLO-KROME or UNBRAKO brands as both are US made and have successfully proven themselves in the field over many years.  Most hardware store stuff is made overseas and you never know what you are buying or what steel was used to make them.

 

Sorry for the rant  :soapbox:

 

From beginning to end...Advice right on target!! :handgestures-thumbupright:  :handgestures-thumbupright:

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I always without fail run a very good tap in every headbolt thread and use grade 5

bolts with the thick washers mentioned before. Reason for grade 5 I had a very good engineer

explain to me if heat treat is missed just a tad grade 8 can be very brittle. I do use grade 8

many places but trust 5s in the block. I do oil the threads and under the head of each bolt

and if I just cant come up with the thick washers and have some good bellvile washers

these will maintain tension very well.

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At this time I opted for the grade 8 from Fastenal.. they did not have any grade 5 in 2 1/4" length. So far so good. This is more of a fun/show tractor not a work horse and we will be keeping a good eye on it in the event there is a problem with the headbolts in the future. At this point though all seems well.

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Good to hear. :handgestures-thumbup:

 

A question for you -- completely off topic, just wondering...

 

I have an old mantel clock that isn't working right now.  A while back, I set it to exactly the same time that the clock in your avatar is indicating.  It's significant for me, is it significant for you? :popcorn:

 

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A question for you -- completely off topic, just wondering...

 

I have an old mantel clock that isn't working right now.  A while back, I set it to exactly the same time that the clock in your avatar is indicating.  It's significant for me, is it significant for you? :popcorn:

Here's a hint..  "inside, outside, leave me alone..inside, outside, nowhere is home. inside, outside where have I been? out of my brain on the ____..!

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YES! :music-guitarred:

 

And since you showed me yours first, I'll show you mine now...

post-4371-0-95109100-1383334844_thumb.jp

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Update.. after running the Tecky 6 with it's new Fastenal Grade 8 gold cadmium headbolts for a few days a few times a day (still breaking it in).. The headbolts are great with no loosening. And with the gold cad plating they look pretty sporty too!

WH50_zpsaef2637d.jpg

Edited by Patrick Reese

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