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6 hp ,no compression,,why?

865 Views 7 Replies 4 Participants Last post by  flash5153
I have a older tecumseh OHSK60-71505c
It's a 6hp on a Ariens snowblower.

I just bought it from a guy that said it had been used maybe,twice and then set in the garage for years and years!!
I believe him. It looks like it is brand new.
It had gas still in it,,smelled like turpentine.


When I first got it,, I emptied the bowl and squirted some fresh gas in and it fired up for a second.So I rebuilt the carb,,,and now it wont fire at all.

It is getting spark and gas. So I checked compression. It is at 40 pounds. I put some oil in cylinder and tested it again. It did not change at all.

I pulled the sump cover and there is no hole in the piston and the rocker arms are not holding the valves open. They are to lose if anything. It has OHV.

When I had the sump cover off,,I didnt think to check for a compression release of some kind.

I do not believe the rings are worn.Or broken. I didnt see any sign of that in the pan or cylinder wall.

I am thinking either the head gasket is blown badly,,or a valve is stuck open for some reason.

I will be pulling the head tomorrow.

Anyone care to guess what the problem could be??? Everything I have looked at so far looks like brand new!!

And does anyone know what the compression should be at,, on this engine??

I must say,,,I really thought when I rebuilt the carb this engine was going to start up and run well. I am surprised to be where I am at now.
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Stuck valve.
I was actually thinking that too,,but as I think about it. The valves are working,, and they seem they are closing . But I will know more when I tear it apart.
Maybe something is hanging it open just a little tiny bit.
A leaking head gasket is a common problem on ohv engines, it generally fails between the cylinder and push rod chamber where the wall is thinnest.
I would be looking for a stuck valve, or something pulled into the intake that is keeping the valve from seating. I have seen the O-ring from an air cleaner wrapped around an intake valve. Wouldn't run. Very poor compression also.
But an engine that sat still for a long time may have some oil breakdown and oxidation or acid corrosion over time if there was any condensate in the oil.
I may be mistaken, but don' think engines that small had a compression release.
tom
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I have figured this out,,I think. I had it running this morning,,and it really sounded good. I could only run it for a few seconds because I ruined the sump gasket when I took it apart.

I put it back together leaking a little ,,just enough to test it.

I dont want to say anything more until I am sure. Off to get a gasket.

You wont believe what I found.(it's not good on my part,,I made a bad mistake )
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I haven't got the gasket yet, but I will tell.

I realized ,,,as I was starting to remove the head,,that I didnt hook the linkage up to carb. I remember hooking it up ,,but it must have fell back off.

It's in the back of carb ,,so you cant see it once it is installed. I didnt notice it ,until I took the muffler off.

It's a very short rod from governor arm to carb butterfly!

When I seen that ,,I figured I would put it all back together and try it. And it started and ran like a champ.

All I can figure is,,I flooded the carb before when I hand fed it gas. And there must be some type of compression release. I tested this with 2 different gauges.
I doubt this runs on 40 lbs of compression.

Like I said,,I wont know 100% until I get it together and run it for longer than a few seconds.

Here's a pic of that linkage.

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