Small engine gear heads HELP

[dwna1a]

So folks I need some help understanding an issue with my 18hp Duramax. Does a single piston engine have to be timed? How? The compression stroke is so hard it’s burned up the starter. I’ve adjusted the valves and double checked them. I might pull the head off and see what I find, bent push rod or valve. I just don’t know.

 

[techmitch]

Is this your engine?
https://images.homedepot-static.com/catalog/pdfImages/ac/ac248b8a-09e8-4891-891d-622a22ee79ac.pdf

 

[dwna1a]

Yes.

 

[techmitch]

I see valve timing and lash/clearance on page 34. Still reading...

 

[techmitch]

Do you have a part's manual for it? Hopefully a link to it.

 

[techmitch]

Oh, what's the problem?

 

[dwna1a]

It appears as if a Honda GX390 head assembly is the exact same as DuroMax. I’m still reading

 

[dwna1a]

On the compression stroke it seems as if it can’t turn passed it while trying to start the motor. If I pull the plug the motor turns very easily. Replace the plug she won’t turn. Valves are working. Motor was running fine yesterday.

 

[techmitch]

It appears as if a Honda GX390 head assembly is the exact same as DuroMax. I’m still reading

As to your original question, the only 1 cylinder gear driven timed engines that I am aware of, (think lawn mowers and mini bikes) was that that some times, if you hit something or it backfired, it could shear the key between the crank and the flywheel which acted as the stator on the inside for the magneto mounted underneath of it.
Some times the flywheel would only move a little bit on the shaft after the key broke and then the flywheel seized on the shaft, off by who knows how many degrees.

 

[PlayDate]

Sounds like a valve is stuck closed. If you adjusted the valves.....did they open and close properly as you turned the engine with the spark plug out?

 

[techmitch]

On the compression stroke it seems as if it can’t turn passed it while trying to start the motor. If I pull the plug the motor turns very easily. Replace the plug she won’t turn. Valves are working. Motor was running fine yesterday.

Missed this post. John is on to something here but what has changed?

 

[dwna1a]

Valves are doing just fine, I even had my Merc mechanic check my work. I’m also thinking the is a valve issue, bent is my thinking. Or a push rod. I’ve pulled the motor out and put my backup 18hp in its place. Now I just need to learn how to work on this one

 

[Nater Potater]

I believe those have a "decompessor" to assist with starting. There's a spring-loaded weight on the cam drive gear that modifies the compression when down at low cranking speeds. If its return spring breaks, the weight will kick out as if it was at speed, thus ramping the compression back up. That would definitely make it hard to start.

 

[techmitch]

I believe those have a "decompessor" to assist with starting. There's a spring-loaded weight on the cam drive gear that modifies the compression when down at low cranking speeds. If its return spring breaks, the weight will kick out as if it was at speed, thus ramping the compression back up. That would definitely make it hard to start.

Do you have a part's manual for it? Hopefully a link to it.

Exactly why I asked this question eariler.

 

[blaster]

Without compression release some small engines and motorcycles are a bucking bronco to start.

 

[Scott215]

Yeah like the old Honda XR600s that have the compression release on the handlebars

 

[Nater Potater]

Yeah like the old Honda XR600s that have the compression release on the handlebars

Even my wife's '87 XR200 has an auto incorporated into the kickstarter.

 

[Wanderer 290]

Check the valve lash. Some engines have .005 bump on the cam to assist in compression relief when starting so a slight out of adjustment will make for a difficult start

 

[techmitch]

Check the valve lash. Some engines have .005 bump on the cam to assist in compression relief when starting so a slight out of adjustment will make for a difficult start

Is this your engine?
https://images.homedepot-static.com/catalog/pdfImages/ac/ac248b8a-09e8-4891-891d-622a22ee79ac.pdf

Yes.

I see valve timing and lash/clearance specs. on page 34. Still reading...