replace starter clutch bolts before they sheer or not?

[katman]

Some believe that changing your starter clutch bolts to a harder bolt is a good idea to prevent sheering and damage. As I do.

Others believe it isn't a good idea but there is lots of experience here so read the wisdom and make your own decisions.

There seem to be good arguments for both. I think it is worth looking into.

[earlfor]

Re: replace stock starter clutch bolts before they sheer

I have replaced starter clutch bolts. The only cause I have been able to determine for broken starter clutch bolts is a faulty petcock. Fuel seeps into the combustion chamber, you press the starter and the pistons hydrolock. The starter clutch bolts sheer off. That is a good thing.
If they did not, you could risk bending connecting rods. Better to use the stock, softer bolts. Compared to tearing down an engine to install new rods, starter clutch bolts are cheap.

Earl

for the gs1100 and prob. the gs750 of the early 80's era you should replace your starter clutch bolts. There are three allen head bolts holding on your rotor and they can sheer and destroy many things including your wallet.

I have three here and checked the bolts and they have no stamp on them for hardness. You want to get a 12.9 rating which is the hardest made. it is stamped on them.

it is a bit of a pain because you have to take off your stator cover, pull your stator rotor off which requires a puller and on the back you will find the bolts.

IF you engine is in for winter upgrades or any work to be done consider this mod.

[Anonymous]

bolts

I have to agree with earl on this one I would only say to pull the cover and unit and check there torque, mine where loose when I did my trans bearings, but showed no distress, as far as shearing

[katman]

Mark over on performance mods has a motor that sheered the bolts and his starter cog let go too throwing shrapnel everywhere.

I have heard of them letting go under throttle and and that, I don't think is good.

I haven't had it happen to me but have had a few share there plight. I have had a couple of drag racers suggest this to me so I thought I would post it.

I hope I haven't spoken in error.

[scotty]

I have also seen where they back out and shear off causing loyt of damage. When my starter dreive let go i was fortunate to find a used omn at the speed shop. It had the bolts spot welded

[earlfor]

Scotty, my clutch bolts are blue Loctite'd. The stuff does not vibrate out.
If I was worried, I would use red Loctite, but I would'nt weld them in place.
Then too, things drag racers do are not always a good idea for the street.
When things break, replacing the broken part is only half of fixing it. If you dont eliminate the cause, you havent fixed it.

Earl

I have also seen where they back out and shear off causing loyt of damage. When my starter dreive let go i was fortunate to find a used omn at the speed shop. It had the bolts spot welded

[scotty]

Scotty, my clutch bolts are blue Loctite'd. The stuff does not vibrate out.
If I was worried, I would use red Loctite, but I would'nt weld them in place.
Then too, things drag racers do are not always a good idea for the street.
When things break, replacing the broken part is only half of fixing it. If you dont eliminate the cause, you havent fixed it.

Earl

I have also seen where they back out and shear off causing loyt of damage. When my starter dreive let go i was fortunate to find a used omn at the speed shop. It had the bolts spot welded

I hate to agree with an Irishman but i must on this.

[earlfor]

There, there Scotty, take a couple aspirin and lie down for a bit.

Earl :-)

I hate to agree with an Irishman but i must on this.

[Anonymous]

There seem to be good arguments for both. I think it is worth looking into.

The best choice depends on some things.

1) It can be a good thing to have a safety valve in the system to prevent catastrophic damage in the event of an overload. If the bolts are significantly softer than the crank, they will usually fail without doing a lot of damage to the crank itself. Then the broken bolts can be extracted and the crank re-used with new bolts. That saves an expensive part from hitting the garbage.

2) This sounds to me like an issue of the bolts backing off, then failing, not inadequate bolts. This is a common failure sequence and it can be avoided by properly torquing the bolts and using Loctite, as previously suggested.

3) The 12.9 bolts will be less ductile than 10.8 (10.9? memory fails me at the moment) grade, which will make them more likely to fail from fatigue cracking over time. This should not be an issue if they are torqued properly and don't come loose, but that seems to be a problem from the descriptions of failures here.

4) the 12.9 bolts may be hard enough (given the yield strength of that material, I think they will be) to do significant damage to the crank end in the event of a failure, which may trash it and cost more in the end.

My choice would be to use new OEM grade bolts and make sure they are properly torqued and secured with Loctite. I bet either way is OK with proper torquing and use of Loctite to prevent loosening over time.

Mark

[katman]

Re: replace stock starter clutch bolts before they sheer

I have replaced starter clutch bolts. The only cause I have been able to determine for broken starter clutch bolts is a faulty petcock. Fuel seeps into the combustion chamber, you press the starter and the pistons hydrolock. The starter clutch bolts sheer off. That is a good thing.
If they did not, you could risk bending connecting rods. Better to use the stock, softer bolts. Compared to tearing down an engine to install new rods, starter clutch bolts are cheap.

Earl


Earl,

can you explain the hydolocking and how the rods can get bent??

[earlfor]

Re: replace stock starter clutch bolts before they sheer

Liquid doesnt compress. With the momentum of the starter pushing the pistons up, they cant get to TDC and come back down if they are tyying to compress fluid. They stop instantly. The sound is just like what you would hear if you hit a 55 gal barrel with a 5 lb hammer. It will jar the whole bike.
Ask me how I know. :-) There is enough force to bend a rod or wrist pin.
It doesnt do the crankshaft bearings any good either. heh

Earl

can you explain the hydolocking and how the rods can get bent??

[katman]

so you are talking about the cylinders that have filled with gas and are on the compresion stroke being unable to move?

the starter motor has enough power to sheer bolts and bend rods?

[Anonymous]

bolts

Having tore down alot of bike engines of all makes I have found that most had loose bolts!! (Owned a salvage yard) most of the ones that were really loose showed signs of shearing, (cut marks in the thread area) these where replaced, the ones that were just starting to loosen, did not have these cut marks were reused, with out problems, I think that once they back out the load shifts from the tapperd head area and mating surfaces to the bolt shank and you have failer.

[Anonymous]

I think that once they back out the load shifts from the tapperd head area and mating surfaces to the bolt shank and you have failer.

Actually, if they are torqued properly, the bolts see NONE of the torsional load. All of the force is transmitted by friction between the two pieces being clamped together and the bolts only see tension as they clamp the pieces. Once the preload is removed (ie. - the bolts back out), then the force IS transmitted through the bolt shank and you begin a fatigue cracking failure that eventually has the bolts break off and catastrophe ensues...Not cool.

All this can be avoided by careful use of a torque wrench and a thread locking compound. Very cool.

Mark

[katman]

This is great buys.... it all makes very good sense.

Loc-tite and proper torque will elimintate the sheering problem is what I am getting out of this.

So I have reversed my original oppinion, puting the stock bolts back in that are in excellent condition...good information.

thanks guys.