Rebuild advice for H70-130000

H

heavy4x4

New Member
#1
#1
Hi all,

Have an older H70-130000 Tecumseh engine in a Retek Cheetah.

The engine does run, sorta, but the compression is not where I think it probably should be. Mind you the engine is very old. I found a part number online for a set of 0.010" oversize piston rings and am thinking about installing them. Would that be a horrible idea if I actually didn't get the cylinder bored out?

Also, if I'm going in to replace the piston rings, I figure I'll need a new head gasket. Anything else you can think that I should order? I'll have to pull the connecting rod from the crank, so maybe rod bearings? Head bolts?

Thanks for your help,
-Steve
 
J

jimh

#2
#2
If you're going to rebuild it, you should check the cylinder to see how out-of-round it is and how much wear. Too much cylinder to piston clearance will mean you need more than rings. To use the .010 parts, it should be bored. If rings is all that's needed, you'll need a head gasket and timing cover gasket. You have to remove the timing cover to unbolt the rod. There are no rod bearings. The rod just clamps on the crank. It would be a good idea to also check the rod journal of the crank for out-of-round too. It may need ground and an undersized rod. Good luck:thumbsup:
 
oldfatguy

oldfatguy

Active Member
#3
#3
If the engine is not smoking and the cylinder isn't scored then leave it as it is.Your low compression is most likely the valves are not sealing and it's time for a valve job.First check to see if they are,With the muffler off put you thumb on the exhaust port and pull the starter rope.If you feel it suck air thru the exhaust port it means that the valve is leaking it may even feel like there is more compression when you seal the port.Usually it is caused by carbon build up on the valve and seat.You have to remove the valves and clean and lap them in to get a good seal. If you need more info on how to do that let me know and I will tell you how to do it.
 
H

heavy4x4

New Member
#4
#4
oldfatguy - thanks for the advice. I hadn't thought about valves being a possible cause.

I'm pretty handy and know my way around an engine, but I could certainly use any instructions/tips/tricks you have for lapping the valves in this Tecumseh.

Thanks in advance for your help,
-Steve
 
milo raptors

milo raptors

New Member
#6
#6
take of spring retainer pull the valve out clean seet and valve put laping compound (rough) on valve and seet take the laping tool put the valve in twist it around wile aplying light pressure take it out clean it off put a lesss grity compounds on repeat clean very good put spring an retain back in and fire er up
 
5

5hpminitech

Member
#7
#7
every old flat head i take apart needs a new exhuast valve due to stem is worn lap al you want but if it sloppy in thew guide it wont seat right plus on techs the face is usually groved it at least needs cutting also dont yank the valve through the guide if it dont come easy the retainer makes burrs you need to file off so you dont ruine the guide
 
H

heavy4x4

New Member
#8
#8
Thanks for the advice and the help.

I pulled the head off. Cylinder looked great! There was, of course, a bunch of carbon and gunk in the valve area and combustion chamber. I cleaned all of that out really well and did a cheap-man's valve lapping (did it in the engine without taking things apart. Seats look great now. And, the valves are in great shape: no side-to-side play.

The carb also went through a 2-day soak in a parts washer. I'm about ready to start reassembly. I'll drop it into the bike and try and fire it up to make sure everything works well before I spend the time to do the bike-portion of the rebuild.

Anybody happen to know what the torque spec is on the head bolts? I was surprised by how easy they were to remove...want to get them installed back at factory spec!

Thanks,
-Steve
 
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