85hp yamaha cylinder head

[robkeiran]

Hi Could somebody tell me if the head bolts can stretch and also how tight should the prv valve should sit in the head cover. Thanks in advance Robert.

[rodbolt17]

on a 2 stroke 85?
nope your not going to stretch the head bolts.
the valve should be a loose fit.
if its not remove the grommet.
clean the grommet pocket.
replace the grommet.

[boscoe99]

What?

Bolts do stretch. That is how they do their job.

Think of a bolt (could also be a stud or screw) as a very stiff spring. A spring that is stretched so as to clamp two parts together. The amount of torque (lb-ft/N m/etc.) determines the bolt stretch and thus the clamping force.

Now just like a small coiled spring that can be stretched too far and damaged, a bolt can also be stretched too far and damaged. That is one of the reasons why a torque wrench should be used. To make sure the bolt is stretched enough, but not to much.

[rodbolt17]

at 22ftlbs?
your not really going to stretch an 8mm bolt.
now an angle torque like on a 4 stroke will stretch a bolt.
like the later 4.2L, torque it then another 90* then yet another 90*.
however to do give a bolt length so you know when to discard the bolt.

[cpostis]

Normally using the original OEM head bolt, you will not see any visually "stretch" of the bolt if you use the specified torque steps and sequence thereof. Head bolts must be of original specifications, IE; OEM. They are designed to hold the torque within allowed stretch.

Let me tell you a story:
As an A/C tech I was out on strike for 3 weeks. The VP of the company I worked for did some service on a compressor while I was on strike. He replaced an unloading head with a non-unloading head (not as deep as the original). He bought shorter bolts to allow for the shorter depth. The bolts were bought from a hardware store. When the strike was over, I was dispatched to the same customer and found the compressor leaking from the head gasket. I pulled the head and found the bolts so stretched that they were "hour glass" shaped. Called my boss and told him what I found and complained that some "donkey rear end" not knowing what the hell he was doing screwed up the compressor. That's when he told me he did it and it was done right! I told him "so you're the "donkey's rear end". He told me to pack up my tools and come to the shop to be fired. I took those "hourglass" shaped bolts and threw him on his desk. Never got fired and got the next new service take home truck to use as I wanted.

Bottom line: Use the right OEM bolts, tighten by the pattern and torque specified by the manufacturer. If your bolts show any sign of being "stretched" or damaged in any way, replace them with OEM. Also, make sure your bolt and bolt hole threads are clean and dry.

Now connecting rod bolts, Rodbolt recommends whenever you remove them replace them with new.

[rodbolt17]

now rodbolts are still a replace when removed.
I have broken a few trying to reuse them.
most the Yamaha 2 strokes with rodbolts are about 8mm made of harder steel and tend to snap off the next time you try for 32 ftlbs.
jonny/rudes and mercs will as well.

[pstephens46]

Normally using the original OEM head bolt, you will not see any visually "stretch" of the bolt if you use the specified torque steps and sequence thereof. Head bolts must be of original specifications, IE; OEM. They are designed to hold the torque within allowed stretch.

Let me tell you a story:
As an A/C tech I was out on strike for 3 weeks. The VP of the company I worked for did some service on a compressor while I was on strike. He replaced an unloading head with a non-unloading head (not as deep as the original). He bought shorter bolts to allow for the shorter depth. The bolts were bought from a hardware store. When the strike was over, I was dispatched to the same customer and found the compressor leaking from the head gasket. I pulled the head and found the bolts so stretched that they were "hour glass" shaped. Called my boss and told him what I found and complained that some "donkey rear end" not knowing what the hell he was doing screwed up the compressor. That's when he told me he did it and it was done right! I told him "so you're the "donkey's rear end". He told me to pack up my tools and come to the shop to be fired. I took those "hourglass" shaped bolts and threw him on his desk. Never got fired and got the next new service take home truck to use as I wanted.

Bottom line: Use the right OEM bolts, tighten by the pattern and torque specified by the manufacturer. If your bolts show any sign of being "stretched" or damaged in any way, replace them with OEM. Also, make sure your bolt and bolt hole threads are clean and dry.

Now connecting rod bolts, Rodbolt recommends whenever you remove them replace them with new.

Clean and dry. Some put a little a grease on to ease the job next go around. Are there hard and fast rules on when this should and should NOT be done?

[cpostis]

Clean and dry. Some put a little a grease on to ease the job next go around. Are there hard and fast rules on when this should and should NOT be done?

Thanks pstephens

I stand corrected, what I should have said is "make sure your bolt and bolt hole threads are clean and use whatever the manufacturer specifies as a lubricant on the threads, if any." Yamaha specifies to use motor oil on my head bolts.

[robkeiran]

Thank You all for your prompt answers youve been a great help