038 super top end rebuild

[TheTone]

So...I have a few questions
2. When I pull the two crank cases together I will obviously use the new gasket...but should I lightly apply some hylomar sealant or equivalent on both sides of the gasket as well? I’m thinking not but I’ve read plenty on here that says I should...
3. Should I omit the base gasket and measure squish, or should I install the base gasket and measure squish...or does it not matter?

2. I put a thin coat of Yamabond 4 on the surfaces of case and gasket before pulling them together.
3. Do both. Use gasket. Use grease to stick lengths of solder up to edges of 4 corners of piston. Using flywheel to turn crankshaft, turn piston past TDC and back and forth several times. Measure the thickness of the solder in the squish zone. Use a thin solder as close to squish size as possible - gives most accurate results. Now you can use the same solder lengths with the gasket deleted. If the results are too thick and too thin, you can use a very thin gasket such as aluminum coke/beer can to get closer to what you want.

 

[KarlD]

2. I put a thin coat of Yamabond 4 on the surfaces of case and gasket before pulling them together.
3. Do both. Use gasket. Use grease to stick lengths of solder up to edges of 4 corners of piston. Using flywheel to turn crankshaft, turn piston past TDC and back and forth several times. Measure the thickness of the solder in the squish zone. Use a thin solder as close to squish size as possible - gives most accurate results. Now you can use the same solder lengths with the gasket deleted. If the results are too thick and too thin, you can use a very thin gasket such as aluminum coke/beer can to get closer to what you want.

Thank you thetone. I’ve bought some loctite 518 which I believe will do the job as well as the yamabond 4. I use this as well on the base of the cylinder right...whether I use the base gasket or not?
Today I found some time and have gotten this far: -

One bearing in the case and the crankshaft into that bearing. I’m waiting for the loctite 518 to turn up so that I can do the other side and join the cases together. The freezer and heating trick worked a treat, it all slid into place smoothly. Am I right is saying that as long as the oil feed pipe is attached (as it already is), there is nothing else that has to be fitted before I join the cases together? I’d hate to get them together and then find out I have missed something and have to split them again
Also, when it comes to fitting the crank oil seals should I lube the crank shaft to help them slide on smooth or is that not advised?
TIA guys...I’m thoroughly enjoying this

 

[TheTone]

Make sure the oil line and filter are clean and you're ready to put the case halves together. I use a thin layer of sealant on case and cylinder gaskets just because I'm kind of a belt and suspenders (braces for you Brits ) sort of rebuilder. Obviously if you do not use a gasket, the sealant becomes your gasket. I hope the heat method works for you (I would say most people use this method). You will have to work quickly, but can finish the closure with the crankcase bolts. I fabricated a set of case assembly tools like those so graciously proffered by @Mattyo and use judicious heat along with pulling the crankshaft into the case. Remember those case assembly pins for proper alignment. You may want to check this link for the PTO seal installation:
https://www.arboristsite.com/community/threads/pto-seal-installation-plastic-coke-can.319903/
Best of luck!

 

[KarlD]

Make sure the oil line and filter are clean and you're ready to put the case halves together. I use a thin layer of sealant on case and cylinder gaskets just because I'm kind of a belt and suspenders (braces for you Brits ) sort of rebuilder. Obviously if you do not use a gasket, the sealant becomes your gasket. I hope the heat method works for you (I would say most people use this method). You will have to work quickly, but can finish the closure with the crankcase bolts. I fabricated a set of case assembly tools like those so graciously proffered by @Mattyo and use judicious heat along with pulling the crankshaft into the case. Remember those case assembly pins for proper alignment. You may want to check this link for the PTO seal installation:
https://www.arboristsite.com/community/threads/pto-seal-installation-plastic-coke-can.319903/
Best of luck!

I’m a suspenders kinda guy too

 

[TheTone]

Indeed. Different terminology in British and US English, but the same basic appeal to the male of the species.

 

[KarlD]

I was rained off again today dammit so got on with the saw a bit. I heated the case half and chilled the crank bearing and the case half with the crank already installed. 250 deg C and the freezer for half an hour and the crank cases went together with hardly a tap. I used a new OEM gasket and a thin application of loctite 518. I then fitted the oil seals; I think I put the smaller one in a fraction too far but I cannot imagine it will be a problem? So far so good I think...

 

[KarlD]

I’m getting set to fit the piston circlips now and have a choice; the ones that came with the new piston or the more ‘simple’ ones that I was supplied as OEM. Purely for ease of install I will be fitted the ones that came with the new piston

 

[KarlD]

Oooh...that was easy, now for the other side...twang wtf did that go...WTF did it go...where’s my big magnet...ah there the little bastard is...not so cocky this time...carefully...thank fuk that’s in


Time to nip the cylinder on and check squish

 

[Mad Professor]

I’m getting set to fit the piston circlips now and have a choice; the ones that came with the new piston or the more ‘simple’ ones that I was supplied as OEM. Purely for ease of install I will be fitted the ones that came with the new piston
View attachment 768113

I'd have used the OEM circlips if they fit properly. The ones with the "ears" tend to flop loose at high RPM. Put the ears at 12 or 6 o'clock to minimize this.

BTW, great pictures and nice clean work!

 

[KarlD]

That’s well explained and makes me think I might as well swap them over. I hesitated because I bought them as OEM from LSENGINEERS who do supply genuine Stihl stuff, but they came in a clear plastic bag without a Stihl label, whereas the other OEM parts were all in labelled bags. If I pull them and the ‘OEM’ ones don’t fit I’m screwed though, I wouldn’t refit the eared ones

 

[Mad Professor]

That’s well explained and makes me think I might as well swap them over. I hesitated because I bought them as OEM from LSENGINEERS who do supply genuine Stihl stuff, but they came in a clear plastic bag without a Stihl label, whereas the other OEM parts were all in labelled bags. If I pull them and the ‘OEM’ ones don’t fit I’m screwed though, I wouldn’t refit the eared ones

Is the piston OEM? If so the Stihl clips will be fine.

 

[KarlD]

Is the piston OEM? If so the Stihl clips will be fine.

No it’s Episan, which I am told is as good as Meteor

 

[Mad Professor]

No it’s Episan, which I am told is as good as Meteor

Might be a good idea, with aftermarket circlips, to put a micrometer on them and compare wire diameter to OEM. That would give an idea to fitment.

Anybody do this?

 

[KarlD]

Might be a good idea, with aftermarket circlips, to put a micrometer on them and compare wire diameter to OEM. That would give an idea to fitment.

Anybody do this?

Believe it or not I did, all four are near as dammit 1mm dia

I’ve hit a problem tho, the new piston (and the old) are very very slightly under 50mm dia and the cylinder is pretty much bang on 50mm (sorry cannot find my digital callipers). I have nothing I can use to compress the rings that will fit in this tiny space...I can’t compress the damn rings! I have gotten as far as putting the solder on the piston top and that’s it for the moment...stuck. I guess I can try a cable tie on the bottom half of the ring and do them one at a time but other than that I’m pretty stumped. Any suggestions?

 

[KarlD]

Well good idea or not idk but I removed the rings to allow me to do the squish test with the base gasket in place. There was no compression of the solder that I could feel. I’ll remove the cylinder and try again without the base gasket

 

[KarlD]

Or will not having the rings in place void this method?

 

[Mad Professor]

Make up a piston holder/support from a piece of 1" board.

I use an old handle from a tooth brush, sharpened, to work the rings in, it won't mar the piston.

It also helps if you have a third hand.......

 

[KarlD]

Doh my bad...I didn’t have the solder close enough to the edge of the piston. I’ll reset and try again

 

[KarlD]

Make up a piston holder/support from a piece of 1" board.

I use an old handle from a tooth brush, sharpened, to work the rings in, it won't mar the piston.

It also helps if you have a third hand.......View attachment 768136 View attachment 768137

Ah...I see. Sneaky Isn’t it great how we’re thousands of miles apart and never to meet but we’re able to do this together. Thank you for the help

 

[KarlD]

...and still no compression of the 1mm solder. I guess a base gasket delete is in order then. Being my first rebuild I will not go to the hassle of getting the cylinder lowered. Maybe next time. I might buy some thicker solder though and find out what the squish is