15.5hp OHV Compression Issues

Hello.
I need some quick help with my 15.5hp OHV Briggs&Stratton "Turbo Cool" (like me ) Lawn mower engine that has excessive compression. My electric start wouldn't turn the thing over, so I tried it by hand an I couldn't spin it.
I read something about ACR, and valve clearance, but I have no idea how that relates to OHVs.
I'm about to take it apart, so I'll update you guys with what I find.

Thanks a lot!

Does it turn hard with the plugs out? If so, there is some bottom end issues.

Ah ha, see I didn't check. I took the head assembly off without taking the plug out! Stupid.
I do need a new head gasket, a whole load of oil poured out of the cylinder when I opened it.
Anything I should check?

If it was sitting upside down for a while oil may have just seeped in. Otherwise you might need rings. Oil in the cylinder would definitely make it hard/impossible to turn over.

No It's been in the mower all the time.

It's OHV so I can see the gasket part between the push rod hole thingy and the cylinder, and It's corroded.

Would that solve high compression? An oil leak?

BlackMountian88 wrote:

Would that solve high compression? An oil leak?

all lot of extra oil in the cylinder will usually cause the engine to lock up completely.

A slight amount of extra oil will increase compression briefly, especially in a worn engine.

One of the procedures when doing a compression test is to squirt some oil in the plug hole and see if the compression increases.

If it does, the rings are shot. If compression does not increase valves are toast.

Ok, so weather the pressure increases, or decreases when oil was added there is something wrong?

But I will probably blame the acess pressure on the oil. I'm going to put it back together tomorrow (If I can salvage the head gaske) and see what happens. Thanks!

The procedure for a proper compression test
Warm up the engine if possible

Remove all spark plugs and ground the coil(s)

Open the throttle wide open (no choke), fuel off

Install a compression gauge in a plug hole and crank the engine untill the gauge needle stops climbing.

This is your dry compression reading.

If the compression is low, then add a bit of oil to the cylinder, and re check compression,

If compression increases, the rings are shot.
If no increase in compression, valves are shot.

This is your wet compression reading,

Dont forget. You can also back the valves off alittle to start easier

Ok I kinda get it. Thanks.

I've never taken an OHV apart so I don't know how to back the valves out.

the murray i just got had a similar issue its a 15.5 ohv the valves were not adjusted correctly and would not let it turnover fast enough to start ive got a vid up on my channel on how to adjust them

Excellent vid, what size gap did you use?

.004 i didnt put it in the vid because different motors are different gaps usually they are set at 2 different sizes but all the vids i have watched set them at the .004 gap for both i/e

normally exhaust valves are set a little wider to allow for extra expansion

Ok. I can probably google the factory specs.

I did check and the rockers where no where near that wobbley. I will check the gapping tho.

did it run before you had the problem? what i did to re-seat my valves is, loosen up the nuts holding the rockers and re-tighten them down just enough to were the rockers dont easily move by hand. i did this and it fixed my problem, but, like evry1 else said, it could be the rings.

WHOO Just ran it! Felt so good to be out again!

Yes it ran before, but it sat for almost a month.

I took the whole head apart aside from taking the valves out. Cleaned oil out of the cylinder, and Re-gapped the rockers, and put it all together.
Started first turn!

Now I just have to clean the carb (it only runs full choke).

good stuff glad you got it running again

Thanks for the help!

I'll have to post a pic of it now: stuck in a snowbank.

AHHHH! It did it again. It ran out of gas, so I took like a minute to fill it up again, flipped the switch, and the motor whined and didn't run over. Probably needs a new head gasket and rings. Such a new engine tho. Now I'm considering selling the tractor to pay for my 4 cyl project. Humph.