First post: Help! I cannot find an aftermarket TOP END for my Stihl MS251CBE

[kineticforces@protonmail.]

Hello. This is my first ever post. I have 3 questions:
1.) My Stihl 251CBE has provided reliable service, with mostly light use, since 2014. Last week, after a few hours of use, it started smoking a bit, but was still running pretty strong. Then it lost all compression. I tore it down, and as you can see, the top of the PISTON has a HOLE. The cylinder wall was not too badly damaged, and the crank bearings seem OK. I always mixed my own fuel mix, using WalMart 2-cycle oil and either regular or ethanol-free gas. I never accidentally ran straight gas. There was no obvious leak. What was the likely cause(s)?

2.) More importantly, I cannot find an aftermarket version of Stihl p/n 1143-020-1203. The dealer told me there are 3 different versions (see attached). Mine is fitted for a smallish, 3 bolt intake manifold. All I can find is p/n 1207, which is seems to match the larger, 4 bolt intake manifold. A guy on Amazon ran into the same problem. He ordered the only-1203 that Amazon sells, but it had 4 holes, not 3. https://www.amazon.com/SeekPro-Cylinder-Assembly-Replacement-11430201207/dp/B07D4MZQ3H

3. If y'all are unable to help me find -1203, can I simply replace it with a -1207, and it's matching 4-bolt manifold?

 

[Bob Hedgecutter]

I dunno if I would be looking for a new top end- aftermarket especially.
That has been well cooked by the piston photo and the exterior colour of the cylinder.

Without the saw in hand, hard to claim the cause- but I have seen keyway shears do similar- saw kept running but timing was out far enough to generate huge heat.
Is the con rod kinda blue looking?

Pre ignition would be my diagnosis off evidence provided.

 

[thompsoncustom]

you said the cylinder wall was not to badly damaged? Got any close up pictures? Wondering if the OEM cylinder can be saved.

 

[DND 9000]

If I understand you right your serial no. is 297573655. That means you have a saw before some changes were introduced. That means you can not use the cylinder 1143 020 1207, you have to use the older version 1143 020 1203. There are some more changes between new and older versions and newer parts are not backwards compatible for older versions.

 

[coffeebrk]

I dunno if I would be looking for a new top end- aftermarket especially.
That has been well cooked by the piston photo and the exterior colour of the cylinder.

Without the saw in hand, hard to claim the cause- but I have seen keyway shears do similar- saw kept running but timing was out far enough to generate huge heat.
Is the con rod kinda blue looking?

Pre ignition would be my diagnosis off evidence provided.

Agree with you. OP has parts saw now. List parts for sale and go shopping.

 

[kineticforces@protonmail.]

Thanks for the replies, Gentlemen. In response, I have added a few photos to show the crank/connecting rod as well as the cylinder walls.

Yup, it may be that I now have a parts saw. But it's hard to walk away from ~$450, so if I can find any aftermarket parts, I would like to at least have the option of rebuilding it.

 

[sean donato]

Best advice I can give you with the current situation. Sell the 250 for parts, or better yet throw it In the trash. I know, I get the $500.00 investment. College is expensive too. The ms250/1 is a boat anchor of saws. Looks for a tidy ms260/1 used or buy a new one.
Not what I would do, but see if you can get everything from the newer serial number and retrofit it to your saw, if possible. Aftermarket will not be a viable option for the older style cylinder.

 

[HarleyT]

I just sell the cylinder/piston with the intake manifold intact, for that reason.
This is the current version.

 

[kineticforces@protonmail.]

Harley: do you think my saw will accept the newer version, if I am able to find a matching intake manifold ?

 

[HarleyT]

Harley: do you think my saw will accept the newer version, if I am able to find a matching intake manifold ?

Yes, that is why I keep the manifold with the cylinder, so when the guy gets it, it will work.