# 090 Stihl ??????



## 379 pete

Hi, I recently tore down an 090 Stihl for a rebuild, The crankshaft has 2 weights added to the crankshaft counterweights, look like they were TIG welded on, and are Not factory. Is there anybody out there that can explain how balancing works, Was this done to compensate for a heavier piston or higher RPM's???? I didn't get the piston or jug with the saw, so I don't know what they had for a top end on this case. I would like to reuse the crankshaft, but don't know how it will act with a stock piston. I am thinking that this was an attempt to build a Hot Saw at one time. Any help would be great. Thanks/379 Pete


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## slabmaster

Interesting.That would be for balancing.Is the crank knife edged? That would be the most likely reason they are there.To make up weight that was taken off the crank.Do you have a picture?Are they inserted into the sides of the counterweights? Usually a hole is drilled and heavy metal slugs are inserted.Hope this helps,Mark


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## 379 pete

Thanks Mark, Its really strange, the crank looks totally stock except for the two weights added. They are about 3/16" thick and are welded to the insides of the counterweights, leaving just enough room for the rod to pass thru. Some of the older 070 & 090 crankshafts had similar weights that bolted in with countersunk allen bolts, but this is a newer crank that didnt use that system. The only ideas I can come up with is that it was done to gain a higher RPM, the stock engine was governed to 7000 RPM max. or to compensate for a lot bigger heavier piston??? I just dont know all that much about how balance in an engine works. I can get pictures, if I can figger out how to post them. Thanks/379 Pete


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## Bill G

Here is a new 090 crank I pulled off the shelf. Does it look like this?

Bill


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## 379 pete

Hi Bill, The weights are built like that, But they are welded in, and there are no drilled holes for the bolt on type weights. There is about 4 or 5 different crankshafts that were over the span of the 090. The newest style is like the 066 ect. and are pressed together, yours is the older forged 1 piece. Its got me stumped. Thanks for the reply/379 Pete


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## Bill G

Please post some pictures. I have 090 saws of various ages so I would like to see what you have.

Sincerely,
Bill


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## 379 pete

Hi Bill, I looked closer at you picture, I think thats the new style thats pressed together with the one piece rod. Mine is the older style with the two piece rod. I will get some pics. later. Thanks/379 Pete


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## 379 pete

Pictures of crankshaft


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## Bill G

379 pete said:


> Pictures of crankshaft



I would personally not run that crank. It looks like a accident waiting for a saw to occur in. I am sure other will weigh in but that looks like a "backyard fix"

Bill


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## ozflea

Mac did the same thing on their SP125C saws to ease vibration frst were glued and screwed second lot welded to stop crank failures


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## Macmuncher

My 20 cents say that they were welded in to increase crank case pressure, normally only for racing applications where the saw did not run long.


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## slabmaster

Macmuncher said:


> My 20 cents say that they were welded in to increase crank case pressure, normally only for racing applications where the saw did not run long.



I agree.That is a racing mod.Done to lower crankcase volume,increasing presure for higher rpms.I don't think it would be good for a work saw though. Mark


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## 379 pete

Thanks Guys, That makes the most sense I have heard yet, Lower crankcase volume !!!!! Somebody put some time into doing the modification. The saw came from Washington state, does anybody recognize their work ??? Think I should put it in, add a snowmobile carb., unhook the governor, see how it acts at 12,000 RPM ????? 379 Pete


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## Dibbs

379 pete said:


> Think I should put it in, add a snowmobile carb., unhook the governor, see how it acts at 12,000 RPM ????? 379 Pete



If you want to see a heavy Steel Flywheel leave your saw through the crankcase then that is the best way to do it!


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## olyman

Dibbs said:


> If you want to see a heavy Steel Flywheel leave your saw through the crankcase then that is the best way to do it!


 and what 090's are worth---------------N O T !!!!!!!!!!!


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## ozflea

A reason for the counterweights is it's adds extra torque when cutting makes the engine hang on underload the Karters do this mod to their kart engines to help them maintain higher revs with more torque i have extra tungsten shaped counterweights here that i get welded on .... i would say use the crank you have i feel there's nothing wrong with it.

Mc Bob.


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## sefh3

QUOTE=busdtset;2239395]Hi, all I am new in this forum, nice to meet you all .----The King of Queens[/QUOTE]

:spam:
:spam:
delete em mods


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## trappermike

The best place for that crank is on the shelf above the fireplace,a conversation piece.Some mystery-cool.


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## Naked Arborist

*SCARRY!!!!!!!!!!!!!!!!!!!!!!! Crankshaft!!!!!!!!!!!!!!!!!!!!!!!!!!*



trappermike said:


> The best place for that crank is on the shelf above the fireplace,a conversation piece.Some mystery-cool.




I'd have to agree with trappermike on that one!! I've done crank mods on many SBC engines and had some done for me. The thing that bothers me most is the lack of a solid weld on the crank weights. They leave the door wide open for failure from not being solid welded. If you did want to run it, I would solid weld them down and have the crank magna-fluxed shot peened and weight balanced for the rod and piston assembly that you would be running. That thing looks like an bomb waiting to go off !!! If it does come apart you run the risk of being killed.


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