Hello, this is my first visit here, and I need a little help. I have a Cub Cadet Chipper, Shredder, Vac with a 8 hp Tecumseh engine model HM80 Xl engine. Compression is 45 psi, and the engine back fires through the exhaust only (fire and noise). Pulled the head off and removed the valves and lapped them with "Clover Brand" type C compound. Replaced them but still getting the back fire. This engine has run well in the past, and the motor has not been tore down so it should be timed correctly. Does anybody have a service manual for this engine, or some suggestions. I hope to get it running before the leaves fall as I use it to help clean the yards of retirerees with out charging them. Any help would be appriciated. Thanks KC in Mich.

Pull the flywheel and check the key. Sounds like the keyway is damaged.

45 psi is a little on the weak side.

Did you check the valve lash?

I think you might not have any clearance particularly on the exhaust valve.

Ya know the key on the flywheel is a good approach, as I was using the chipper last when this firsted started, it may have sheared the key enough to throw the timing off. I will check that first, then I will set the piston at BDC and use my compression gage fitting to inject compressed air into the cylinder and see what it holds. The valve lash should have .080" .010" clearance correct? Does anybody know where I can get a service manual for this engine as a free down load?

Does anybody know where I can get a service manual for this engine as a free down load?


http://www.cpdonline.com/692509.pdf

From the helpful links thread on the 4-cycle section of this forum.

Just an update, the Tecumseh engine has a internal compression release, so the engine has to be spun backward to get an accurate compression read. It is reading 90+PSI when spun backward, was 45psi in the normal rotation. I made a pressure fitting from a sparkplug and put nitrogen into the cylinder and found that the exhaust valve is leaking badly. I will try and lap it in one more time,and if I can't get a good seal I will take the valves in for grinding. Thanks for the manual, I like to know the specs. when I put these things back together.

Final report, I had the valves reground ($12) and lapped them in again, compression still at 90+psi. Started the engine,reset carb adjustments to 1 5/8 turns rich,and ran up the RPM's. No bang, let it run at fast idle for 15 minutes then ran up the RPM again and tried the chipper and vac. Oh when things go right life is good, Thank you God. and Thanks for your help. Now to wait on Fall, its 80 degrees and sunny up here so gonna do a little Flying. Take care, KC in Mich.

Do these threads just stay here?

Do these threads just stay here?

As far as I can tell. This way someone can search the threads to see if there is information already posted that they might need, rather then starting another thread that covers the same basic info.

Can I get the repair manual for the hm80 tecumseh 8hp because I have 2 at home but just can't seem to find them so if you could send it to me i would really appreciate it and it would help me out a ton so that i can get it back into running order. Thank you so much.

Can I get the repair manual for the hm80 tecumseh 8hp because I have 2 at home but just can't seem to find them so if you could send it to me i would really appreciate it and it would help me out a ton so that i can get it back into running order. Thank you so much.

The link below should be the one you need. Have a good one. Geo

http://www.cpdonline.com/692509.pdf