Stihl cylinder gaskets 044 vs 038

[Andy171361]

I rebuilt my Stihl 038 Magnum last winter. The new cylinder gasket was what I would describe as being made of fibre or thick gasket paper.  Now I am rebuilding a Stihl 044 and the gasket is made of metal.

Can anybody tell me why Stihl switched from fibre to metal cylinder gaskets and what the advantage of the metal gasket is? 

[joe_indi]

I think the metal gaskets arrived on the newer saws the 044 onwards. The advantage of the metal gasket is that on the newer faster revving saws there is no risk of gaskets blowing. The metal gaskets being thinner, give a higher compression.
On the 066/660 you have the choice of the lo compression paper gasket or the high compression metal gasket. But, there is nothing 'modern' or 'ancient' about the gaskets because the 381, the current form of the 038 (with the 52mm P&C) still have the paper gasket.

I have however found more advantage with the metal gaskets, with a thin coat of liquid gasket on both sides a used metal gasket is still useable, many times more.
Joe

[Andy171361]

Hi Joe.  Thanks for your reply.  I was hoping to hear from you as I always value your practical advice on chainsaw maintenance.

When you talk about liquid gasket would something like HYLOMAR BLUE work or is there a specific liquid gasket for chainsaws?  I used the official Stihl sealant when I attached the manifold to the cylinder.  This came in a tube called DIRKO and seems quite a rubbery/elastic compound, but would that be suitable for the cylinder gasket? (HYLOMAR is much more tacky and less rubbery.)

The reason I asked my original question is that I bought a Stihl 044C as a non-runner, with a scored piston and cylinder.  I stripped the saw followed the advice of several different postings on FF and reassembled with new impulse line and piston rings.  I got the saw going and then tuned it with my a Tiny Tach to a maximum of 13,000 RPM.  Plus I used a fuel:oil ratio of 25:1.

The saw worked really nicely.  It idled well, picked up well and I felled one tree with it.  When I went to re-start it a little while later it did not fire straight away, so I decided to strip it down again and check everything was OK.  It seemed pretty good with some evidence of parts of the piston being a bit more polished than other parts.  As the cylinder is an original Stihl part I decided to play it safe and fit a Meteor piston.  While I was waiting for this to arrive I spent even more time polishing the cylinder.  The only thing I Forgot to do was to order a new gasket.

Anyway I reassembled the saw with the gasket which had been new when I fitted the new piston rings and now the saw will not run as well as it did with the old piston.  It idles erratically and stalls if I adjust the LA screw to let the idle drop below 3000rpm.  And it does not pick up well either.  So as the only thing in the set up that is different is the re-used cylinder gasket I am guessing that must be the culprit.

Do you have any opinions on this or any more top tips?

Thanks

Andy

[joe_indi]

Andy
I found out the expensive way why Dirko was a big 'no-no'.
Maybe it is our climate, maybe I was not repairing saws at 1 per hour, The whole tube of Dirko hardened up after using it on only one crankcase, even though I took the precaution of storing it in my fridge.
Ever since I have been using Three Bond.

When you re-use a gasket on a vertically split crankcase, make a note of how it was before you removed it, what I mean is check the points of the crankcase halves' joints. You will notice that this joint line also is formed on the gasket. So the next time you install the gasket differently chances are that it could leak.
This holds true for both paper and metal gaskets.
I also play it safe by using liquid gasket thinly on both sides of the gasket. I wait for it to become touch dry before installation. Also, to aid in a clean removal in future I apply a bit of grease on the mating surfaces (cylinder and crankcase in this case) to prevent the gasket with its coating from sticking to the surfaces.
I never polish the cylinder too much, I prefer to let the piston and rings do that job. This gives a much better seat, though you need to nurse it through the first tank of fuel.
Did you check whether the rings are snug in the cylinder, ditto for the piston.
Piston without the rings when dropped into the cylinder should move down slowly on an air cushion, when you have the plug hole close with a finger.
Ring tips should show only a hairline gap when they are pushed down with the piston to a point just after the exhaust port.
While you are doing all that, pour in any non H2O liquid of your choice into the crankcase, to the brim. No volatile is better. Place the saw on a paper and check later for any wet spots. Just a basic test for crankcase leaks
You can never know.
Joe

[Al_Smith]

I've reused gaskets and never had a  problem .Keep in mind the crankcase pressure is pretty low to begin with.

General Motors used metal head gaskets for decades .All you had to do is make certain they are clean and not bent .Apply a little grease and tighten them up .

For that matter you can seal a cylinder to base with a layer of Permatex number two and it won't leak .To add to that the old Power Products AH 47 and AH 58 engines had removable cylinder heads .They used no gaskets what so ever .

[Andy171361]

HiAl and Joe.  Thanks for all the info.  I am away from home with work for a few days so I will write a longer reply when I return and have had a chance to look at things.

Cheers

Andy

[Andy171361]

Hi Joe and Al

Here's the latest on my gasket issue!

Firstly I am sorry about your Dirko Joe.  When I store my tubes of sealant I take the nozzle off, cut a piece of thin plastic bag about 1" across, cover the end of the tube with it, then screw the nozzle back on.  I find this helps to extend the shelf life of sealants and glues etc.  You just have to poke out the hardened sealant in the nozzle next time you come to use it.

I did your test of dropping the piston into the cylinder with and without the spark plug hole blocked.  The result was good with an appreciable difference.  I also did your crankcase leak test with some diesel and the level did not drop at all so I hope the seals are OK too. 

The fit of the piston and the movement of the piston rings in their grooves seems normal too.

The only glitch in this (third) reassembly is that the new gasket, a reproduction part, was too large so I ended up retrieving the original Stihl gasket from the bin, giving it a good clean and the re-fitting it with some liquid gasket as you suggested.  I used Hylomar Blue as I had some left over from a car job.  And thanks for the top tip about greasing the mating surfaces - I did that too.

Here's a picture of the gaskets.




 

I have set the carb to factory setting and tested it and it runs well.  Now I need to go and do some cutting with it. 

Thank you both for your help.

Andy

[joe_indi]

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