Is it compression relief or something else - 28D7070123-01 11.5HP

[MowSlow]

I have an old 28D7070123-01 11.5HP engine on an MTD riding mower. When I try starting it, the flywheel only turns part way then stops. I also hear a wheezing sound that sounds like pressure being released. I tried starting once with the sparkplug removed and the the flywheel rotated normally. I removed the cylinder head and rotated the flywheel by hand and it turns smoothly and the valves seem to work. From some internet research I think it might be the compression relief part, but I can't find one in the parts manual, and I'd really like to be sure before taking the whole engine apart. Does anyone have any advice for diagnosing it?

 

[Scrubcadet10]

Do you Know your battery is good?
With the head off, rotating the engine by hand look at the exhaust valve on the compression stroke, it should bump open a little, then close.and then open when the piston comes back up on the exhaust stroke.

 

[Mower King]

Do you Know your battery is good?
With the head off, rotating the engine by hand look at the exhaust valve on the compression stroke, it should bump open a little, then close.and then open when the piston comes back up on the exhaust stroke.

I know what you meant.....

 

[ILENGINE]

A lot of the flat head engines didn't have camshaft based compression release mechanism. they used a cam lobe that held the valve open just a little longer than normal that operates like that all the time. I would check valve clearances and see if they are too wide or not. Most of the L head engine normally close the gaps from seat and valve face wear and will float the valves causing low compression not the issue that you are having.

 

[Scrubcadet10]

ILengine's right, looked at a picture of the Cam, disregard my previous post.

 

[MowSlow]

I would check valve clearances and see if they are too wide or not.

Can you recommend a link with good instructions on how to do that? Most of the stuff I find online is for overhead valves

 

[Mower King]

Can you recommend a link with good instructions on how to do that? Most of the stuff I find online is for overhead valves

If it's a Flathead, most flatheads, you take the valve cover / breather assy off, that is where the lifter meets the valve, there are no push rods. That is where the lash is measured and it is not manually adjustable like a OHV.
When I used to build Flathead racing engines for racing go-karts, I use to file the end of the valve to get the proper measurement but, I didn't care about the lash, I cared about when the valves opened and closed in relation to TDC, on a degree wheel!

 

[Scrubcadet10]

not your specific engine but a good guide on what to do what you'll need

 

[MowSlow]

I checked the valve clearances and they're good per the manual. Anything else I should check?

 

[Scrubcadet10]

can you spin the top of the valve in the seat? place your thumb in the middle of them and try to spin them back and forth.