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MF12H engine question


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#1 KIRO-1 OFFLINE  

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Posted April 30, 2011 - 08:19 PM

I did a compression test today on my MF12. Compression is at 55 psi. LOW I KNOW! However, she doesn't smoke at all. Starts a little hard, but not bad. My question is, before I pull the engine and tear it down, should I focus on rings first or valves. Mind you I have never torn an engine down before so this will be a first for me. Any help would be greatly appreciated :blush2:



#2 MH81 ONLINE  

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Posted April 30, 2011 - 08:41 PM

How did you do the compression test? If you were rolling it over with the starter, it's right on. That engine has a compression release that will put it at 55 or so. release won't kick out until you hit 200 RPM or so.
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#3 DH1 ONLINE  

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Posted April 30, 2011 - 08:49 PM

HH120s have a decompressor in them, how much compression you get at cranking speeds I don't know.
1 thing to check is how much smoke if any is coming out the vent tube on the valve cover when running, if smoke visible from there them rings aren't sealing good enough.
If it doesn't smoke most likely valves maybe not sealing real good???
Are the head bolts tight?
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#4 KIRO-1 OFFLINE  

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Posted April 30, 2011 - 09:11 PM

Thank you so much for the info. Yes, I rolled it over with the starter. I didn't realize there was a compression release valve. I will check the head bolts tomorrow when I get back from picking up the MF7 . Man, You guy's are the best. Thanks again.

#5 FirefyterEmt OFFLINE  

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Posted April 30, 2011 - 10:36 PM

Yea, pretty simple motors really.... With just the one piston, I would not worry about the rings as long as she runs good and does not push smoke. I will have to attack my 12G once the hydro is done, she is starting to push some smoke, more at start up, but now while running a bit too. But she works hard in the snow and mowing...

#6 KIRO-1 OFFLINE  

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Posted May 01, 2011 - 06:08 AM

No smoke at all, so I'm just gonna work her through the summer and do a frame up restoration in the fall when I take my last 3 weeks of vacation. I call em staycations. Always alot of work to do in the fall getting things buttoned up for winter when you have a dog kennel.




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