STIHL 028 Compression spec - spoke to Stihl

[Fish]

Here is a pic of a 42mm, it is slightly domed on top as well.


Is your piston flat on top? Anyone have an 44mm?

 

[sefh3]

Didn't the 028's have a few different piston sizes? 42mm,43mm, and 44mm. I'm thinking he has the wrong piston for that cylinder.

 

[Fish]

Maybe the 2 threads could be merged, might help a bit.

 

[oscar4883]

My 46mm and 42mm look like the above pics. The 44mm ones I have are domed on top. Similiar in shape to the 42mm posted in the above pic. If I had a clue how to, I would post pics.
abl111- I will get that cylinder off tonight and let you know the condition.

 

[spudulike]

Spud - I think 175 psi must be for different saws. Stihl's spec, as mentioned for the 028 is what I 'have' to go with... Maybe it is a 'low compression saw' to begin with ??? I don't know. I have gotten so many different #'s ...

The comp testing I'm doing is with many pulls; 3-5 at least. I am just taking a comp tester ( w/ a schrader valve ) - threading into sparkplug hole - throttle open, 5-10 pulls and reading gauge...
Definitely a challenge...

Yes - 175 psi was on my 345, 630 and Mcculloch california

Spud

 

[abl1111]

Guys I merged this link to the link below - this way it can stay in one link as suggested .... I added a bunch of cylinder and piston pix - tell me what you think.

http://www.arboristsite.com/showthread.php?t=125556

 

[Fish]

Not much of a merge, more like a "yield".

 

[jockeydeuce]

here is a pic of a 42mm, it is slightly domed on top as well.


Is your piston flat on top? Anyone have an 44mm?

I have a 44mm 028 piston here and it's domed too (full hemisphere type dome).........I'm starting to think a piston swap is this guys trouble.

 

[Fish]

Someone just slapped in a 44mm, is my guess. Can you measure from the pin to the top, and the original poster as well. We can see if that may just tell the tale.

 

[ms290]

seems to me he should hit the wood and just find out how well it performs. if it cuts like a banshee why change anything? If it runs like a joke then i would be looking at micing a few things and possibly changing something.

 

[abl1111]

Tomorrow I will put her together, hopefully measure squish and run her under load...

Not sure which pin you're talking about, so I took two measurements ( not w/ a caliper ) - with a ruler:

a) centerline of wrist-pin to edge of cylinder - not to the top of the dome = 2 centimeters

-or-

b) top edge of the top ring-groove in piston to edge of cylinder = 3.5 mm


- and just for S's & G's - the distance from the edge of the cylinder to the top dome of the cylinder is 3.5mm too...

 

[jockeydeuce]

Oops.....Posted this in your other thread by accident.....Try this again!

Let's go back to what Fish was saying for a minute.......

If you're 028 is 44mm bore and has a flat top piston instead of a domed piston like this........


You will never get proper compression out of that saw because someone has stuck a 44mm piston out of something else in there......Can you confirm this, abl1111???

 

[Fish]

Yes, not only the domed question, but the distance from the pin to the top of the "piston", with both, you may be convinced you have the wrong piston and the correct thread.

But that is just my guess.

 

[Rookie1]

Yes, not only the domed question, but the distance from the pin to the top of the "piston", with both, you may be convinced you have the wrong piston and the correct thread.

But that is just my guess.

Your guesses are usually pretty good Fish.Id go with you.

 

[Fish]

Your guesses are usually pretty good Fish.Id go with you.

No, just a case of cold "Milwaukee's Best Guess"....... light.......

 

[striperswaper]

so a 44 running in a 46mm bore is that really possible?

 

[Fish]

so a 44 running in a 46mm bore is that really possible?

NO.....

A piston from another brand/saw, that is not "domed", and has a different
height from the piston pin to the top of the piston, just may be his
PROBLEM

 

[Fish]

But with no data, is just a good guess.

So if we could have a pic or two.

A light coat of carbon can throw the comp. ratio way off, a wrong piston is a real "no brainer"...

 

[abl1111]

Jockey Jockey - My piston looks exactly like yours. Even the "2" I can see, and thru to the inside of the other skirt, mine has 44L and a 24+

I see yours has something written in there too.

------------------------------------------------------------

A few pix of my cylinder and piston:

Thx for sticking in there !

 

[Fish]

pistons look different to me.