Tecumseh HH120 vibration?

Hello-

I have a Tecumseh HH120 (12HP) engine from late 1960's that is in a PUG 4x4 ATV. My concern is the high vibration of the engine when running. It really vibrates the whole machine at idle all way to wide open throttle. I have rattled bolts loose and plexiglass windshield vibrates from the engine.

The engine runs really well, idles well, no smoke, but it has high vibration. Is it possible that the counterbalance gears are misaligned, but engine will still run normal? The previous owner said that the engine was rebuilt at one point, and they never really used it much after that because they bought a modern 4 wheeler.

This engine has a belt drive salsbury clutch like on a snowmobile to drive the machine. I have removed this clutch from the engine thinking it may be the culprit, but engine vibrates just as bad. Also, pulled engine shroud and inspected flywheel, saw no missing chunks or fins.

Any help on this or info would be great. Thanks in advance!

-Jesse
 

This may sound too simple but check the motor mounting bolts and whatever system there is to hold the engine fast to the chassis.
Does it by any chance have rubber isolators that have deteriorated over time?
I bought a log splitter once with an 8 HP Briggs that the Prior owner had let all the engine mounting bolts get loose and one was actually missing.
The resultant vibration was severe enough to crack the weld on engine mounting base.
Unfortunately, the base was welded right to the hydraulic oil reservoir and the crack caused a leak.
 
(quoted from post at 20:49:55 04/29/19)
This may sound too simple but check the motor mounting bolts and whatever system there is to hold the engine fast to the chassis.
Does it by any chance have rubber isolators that have deteriorated over time?
I bought a log splitter once with an 8 HP Briggs that the Prior owner had let all the engine mounting bolts get loose and one was actually missing.
The resultant vibration was severe enough to crack the weld on engine mounting base.
Unfortunately, the base was welded right to the hydraulic oil reservoir and the crack caused a leak.


Thanks for the info on rubber insulators. There are 4 round rubber insulators under each mounting bolt/leg. They do look deteriorated and squashed down. The engine is tight to chasis though. Could these old insulators cause this much vibration if they are tight? Thanks for the help so far.

-Jesse
 
I guess I would observe how much movement there is when the engine is running and where the movement, if any was located.
Kind of reminds me of the snowmobiles back in the late 60s and early 70s with the single cyl. Hirth, etc. engines.
Most were mounted in rubber and the engine would vibrate like the devil when idling.

'course, I could be way off base on this, too! LOL
 
Hi HH120 indicates the engine is a 12 hp flat head, generally these engines run smooth I have several on Sears Suburban tractors they are boltrd direct to the frame no isolaters and are very smooth. I tried looking in my manuals and am not sure if Tecumseh used balance gears in the HH120 engines if they did it and they are not proplerly installed the engine will vibrate terribly if it is an overhaed engine by chance it has balance gears
 

One thing i may try is swapping in my other tecumseh engine. It is a 16hp model oh160 with overhead valves like you said. The 16 hp is in my 68 sears suburban. Putting the 12hp hh120 in suburban would would make it correct.
 
It has been a long time since I saw a PUG. They were well built machines back in the early, mid 70's.

Now to your problem.

Tecunseh used what was known as a DYNA-STATIC Balancing System on those engines. A lot of viberation problems can be traced to the system.

Take to much space and time to explain it all.

You can go to My Mower and download a PDF file for your engine. The balance system is on about page 40 to 45.

https://www.mymowerparts.com/pdf/Tecumseh-Service-and-Repair-Manuals/

Just scroll down auntil you find the VH, HH and OH engines.
 

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