MS250-Too Much Compression?

[drf255]

I'm wondering about a few issues with the saw I'm building. It's the one in this thread:

http://www.arboristsite.com/community/threads/another-porting-question.268134/

I finally got the EZ start mechanism set up. It's runs out of steam at 230 psi compression. It's been cranked over a lot and there's no oil in the cylinder. After the cabers break in, am I looking at something that just isn't gonna run?

The timing was advanced a half a keyway. I'm thinking I have to pull the EZ start off of this thing.

The most worrisome is I have some vertical scratch lines in the piston skirts and the engine hasn't been fired yet. I tried to hit all the edges I posted with a round stone. They were all smooth to the touch before assembly. The entire piston and cylinder were washed thoroughly in soapy water and dried before assemble.

The scratches are more like areas that are polished. They cannot be felt. The aftermarket slug I used doesn't really have any horizontal lines in it like a factory one.

I'm afraid I may have left a ridge on one of the ports?

Will try to post a pic.

 

[drf255]

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[blsnelling]

Why do you even want to run so much compression, especially in a homeowner grade saw? It doesn't take that kind of compression to make a very strong saw. I'm not trying to rain on your parade, just suggesting dialing it down a bit to make it realistic. What ever you do, I wish you the best luck with it. It'll be interesting to see how it runs.

 

[drf255]

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[AKDoug]

Pour some oil into that thing. Did you assemble dry? Those minor scratches aren't going to do a thing.

That compression is too much. You need to grind some of that pop up off in my opinion.

 

[drf255]

The rings were heavily oiled. The cylinder was dry on assembly.

It's all assembled. I'm gonna run it as it.

I didn't calculate volumes when I welded the dome. I just went for it. I didn't think that the small popup I added, especially after reliving it for the plug, would have increased it this much.

 

[blsnelling]

It's a lot easier to pull it apart and do the right thing now, than it is to forge ahead and regret it later.

 

[drf255]

Put a bit of oil in the cylinder.




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[drf255]

I may have to pull it apart. If I run it as is, what's my biggest threat?

Detonation?

 

[AKDoug]

If you look at how how much the tiny popup brad uses increase compression, it's no wonder the huge popup you used has increased the compression so much. Detonation is going to be the issue with this kind of compression. I'm sure there will be other issues that I am not aware of because I've never seen a saw past 220# (and that one detonated on premium pump fuel).

 

[drf255]

Can I try octane boost?

I'm having fun. The piston, cabers and jug cast around $40.

IDK if I should just try it.

If you guys think I'm gonna bend the con rod, I'll just take it apart again.

It's a clamshell, so no so easy to pull the piston.

 

[rob066]

Run diesel LOL

 

[blsnelling]

Those poor bearings!

 

[sunfish]

Run the crap out of it and take lots of photos to post here...

 

[Rookie1]

Run it and see what happens. Keep us up on your progress.

 

[Chris-PA]

Those poor bearings!

Just to play devil's advocate - so he's got an extra 60 or 70psi at cranking speeds. How much extra cylinder pressure does it have at 10,000rpm under load, and how much more load is this going to put on the bearings? I'm not sure one can make a direct correlation between these two vastly different conditions.

 

[kyle.kipple]

 

[Red97]

Run it on nitro, and extra oil, or take it down a notch around the 200psi mark.

 

[chris zautner]

you have to make a video of it running

 

[old-cat]

Blow it up, then try to figure what broke first!!! Don't forget the pics!
Or just take some off the dome and enjoy your toy.