What do you think caused this damage? (PISTON PIC)

[russhd1997]

No one around here offers that stuff... can you send me a fresh tube of the stuff?















Okay, how much does this stuff cost for a tube as big as the large size Ultra Grey? I've been running the 850 with no problems so far on the halves being sealed with Permatex Ultra Grey. I was sure to put some around the bearing shells where they meet the case.

I had more trouble applying the stuff, rather than running problems from it...

+1 on the Ultra Grey. I used it on the bottom end of my MS180 and it is working fine.

 

[blsnelling]

Silicone products are not the proper sealant for case halves or a cylinder. I hear you that you have done so successfully for years, but why risk it. The proper products are easy to get and not expensive. I listed several proper sealants earlier in this thread IIRC. Threebond 1194, Permatex Motoseal, etc.

 

[cpr]

Kyle, et. al.

My ported 101 came assembled with this stuff. If RM can restore 50s Maseratis and Shadow development mule Can-Ams, plus karts and use it...

ThreeBond 1194 Liquid Gasket Sealer 3.5oz

 

[dbittle]

HT75 Squish

OK, I had a chance to measure the squish clearance in a properly running HT75. I got .037" in mine. Compression is 135 psi cold.

dbittle

 

[biggus]

OK, I had a chance to measure the squish clearance in a properly running HT75. I got .037" in mine. Compression is 135 psi cold.

dbittle

Thanks for checking that out. Mine's in at around .033" so I guess it's right there - my psi is at 110 now but w/o gasket.

 

[Smittysrepair]

Thanks for checking that out. Mine's in at around .033" so I guess it's right there - my psi is at 110 now but w/o gasket.

I am kind of curious here seeing I have never messed with one of these trimmers. I am wondering if there is different thicknesses of gaskets available for these cylinders? Because it kind of worries me that it is this close without the gasket. Especially seeing I thought I read earlier that you said the gaskets you have measure .015'' thick. That would mean that originally the squish would have been around .048'' when it was new. I still keep thinking there is another problem here like the rod bearing that is causing this. This is just my opinion though so do not shoot me especially seeing I am no longer a fan of gun shot wounds. lol I do know this has been an interesting topic that you have started here. And I am eager to see a video of it running when you get done with it.

 

[biggus]

So... I'm at 110 psi w/ new aftermarket piston and cylinder, w/o a base gasket - only using permatex between the cylinder and case to get the squish down and it's running great compared to what it was at 70-90 psi. Obviously something is still amiss - I checked that big end bearing on the rod and I can't see 180 degrees around it because of it's location w/o breaking a mirror and sticking a small shard down there; I don't have an inspection mirror small enough.

I hate to say it but if it stays where it's at right now then I can be happy with that. I'll break it in a little, trim a few trees around here, and if it holds up I can give it back to my friend and tell him to get all the use he can out of it till it blows.

I would like to get it up to par but I think I'm done for now. The only options I can see is as others have said: broken crank bearing at big end of rod (yet there is no play) or maybe a slightly bent shaft? Either way it would mean a new shaft and I can't fork out the dough right now for that. Or it could be the aftermarket parts...

Thanks for all the help!

 

[biggus]

I am kind of curious here seeing I have never messed with one of these trimmers. I am wondering if there is different thicknesses of gaskets available for these cylinders? Because it kind of worries me that it is this close without the gasket. Especially seeing I thought I read earlier that you said the gaskets you have measure .015'' thick. That would mean that originally the squish would have been around .048'' when it was new. I still keep thinking there is another problem here like the rod bearing that is causing this. This is just my opinion though so do not shoot me especially seeing I am no longer a fan of gun shot wounds. lol I do know this has been an interesting topic that you have started here. And I am eager to see a video of it running when you get done with it.

Hey Smitty, and I'm sure you're probably right... the only way for sure as I typed as your were typing is to find a teeny tiny inspection mirror or see if I can find a mirror around here I can break a piece off of and stick down into the case.

The gaskets were actually .025" each and there were two stacked onto each other compressed so tightly I mistook it for one every time I disassembled this thing. It wasn't until I cut it off that I realized there were two there. But even with one gasket on I'm calculating squish would've been at .030+.025" =.055".

 

[biggus]

Funny, just found a stihl TI bulletin #32.2001 that says "two cylinder gaskets have been installed in some models. The two gaskets may be replaced by a single gasket in the course of repairs or service work."

 

[Dan_IN_MN]

I hope it gives the church many more years of service!

So... I'm at 110 psi w/ new aftermarket piston and cylinder, w/o a base gasket - only using permatex between the cylinder and case to get the squish down and it's running great compared to what it was at 70-90 psi. Obviously something is still amiss - I checked that big end bearing on the rod and I can't see 180 degrees around it because of it's location w/o breaking a mirror and sticking a small shard down there; I don't have an inspection mirror small enough.

I hate to say it but if it stays where it's at right now then I can be happy with that. I'll break it in a little, trim a few trees around here, and if it holds up I can give it back to my friend and tell him to get all the use he can out of it till it blows.

I would like to get it up to par but I think I'm done for now. The only options I can see is as others have said: broken crank bearing at big end of rod (yet there is no play) or maybe a slightly bent shaft? Either way it would mean a new shaft and I can't fork out the dough right now for that. Or it could be the aftermarket parts...

Thanks for all the help!

Great job! Way to stick with it! I hope it gives the church many more years of service! Good for you for offering to repair it...even though it took more than you thought it would!

 

[Smittysrepair]

Man that scares me even more though if that is the case. I really thought you said .015'' instead of .025''. I really wonder if there could be that much difference between the OEM and aftermarket cylinder, the pistons, or the combination of the two. To bad we did not think to check both cylinders with a depth micrometer and measure the pistons earlier on. You would have known for sure what the approximate squish originally was. I really hope it is not a bearing failing though because it would be a shame for this to happen again. Especially seeing the amount of time and money you have invested in this thing.

 

[ToMang07]

Check the big-end rod bearing to see if that came apart. Also, an electrode could have broken off a spark plug
and caused that. I've seen that happen in the smaller engines before.

That's what it looks like to me. Ouch.:taped:

 

[bigbadbob]

Does your compression gauge have the schrader valve in the tip???

 

[firewood guy]

Are you sure thats the exhaust side? No 2 stroke I've ever worked on had the ring locating pins on the exhaust side. I'd be looking closely at the tops of the transfers to see if they are dinged up at all, my guess is foreign matter intake, Does it have a Zama carb? is the barrel roller intact? That little roller is made of stainless and will chew up whatever it comes in contact with inside a running engine. my 2c

My thought too. The ring pins are on the intake side, not the exhuast (thrust) side!!! Where's that little arrow pointing? Looks like something went in the intake since the score marks start at the top and stop bofore the bottom of the piston skirt, unlike when crank ball bearing retainers fail and the score marks go from the bottom up.

 

[RiverRat2]

I'm hoping to have time to rip into it tomorrow - when I do should there be NO play in the connecting rod bearing at the bottom or is there an amount that is considered acceptable? I know I've wiggled things around before and didn't notice anything really obvious but if even an 1/8" is not acceptable I would have passed that by.

I don't think the clanging is coming from the clutch drum - the sounds is coming from within the cylinder.

side to side there will be a little play on the bigend rod brg.,,, vertically 0,,,,,,,, none, nada,

 

[lone wolf]

Sounds like a rod knock .That explains the scoring and the marks on the rod bottom.You should separate the cases and get to the root of the problem!

 

[biggus]

My thought too. The ring pins are on the intake side, not the exhuast (thrust) side!!! Where's that little arrow pointing? Looks like something went in the intake since the score marks start at the top and stop bofore the bottom of the piston skirt, unlike when crank ball bearing retainers fail and the score marks go from the bottom up.

Piston orientation already addressed. It's the correct orientation.

Does your compression gauge have the schrader valve in the tip???

Yes.

 

[biggus]

Sounds like a rod knock .That explains the scoring and the marks on the rod bottom.You should separate the cases and get to the root of the problem!

Even if I found out it's the crank or bearing - (they're all one unit) - not only can I not afford one (and would rather not get another aftermarket part) I don't know if it would be lucrative after seeing the bill on this thing. If it will run as is for another couple years (this is not a high use saw) then I would consider it a success. Yes, I would love nothing more to completely conquer this thing but the hard reality of it is not enough cash and so I'll have to compromise.

With the total bill for this thing (including the other consumables I've replaced) if I were to buy a new crankshaft + seals for a few more bucks I could've bought a new FS80 or other pro equipment which uses the same powerhead (4137) and just swap it out and sell the new trimmer shell on ebay to recoup. I'll take that into consideration should this ever happen again.

 

[dbittle]

Agree

I think you're making the right call. If it comes apart totally at some point in the future, get a powerhead from ebay and swap it in, or break it down for parts. Appreciate you posting the thread, I've learned a lot following it.

 

[deerlakejens]

I'll second that, this has been a very informative thread. Way to stick with it and really appreciate the photos!