My Tractor Forum banner

1 - 17 of 17 Posts

·
Lifetime Lawn Guy
Joined
·
1,426 Posts
Discussion Starter · #1 ·
Ok, I'm somewhat salty on small engine repair, but when it comes down to major overhauls or specifically diagnosing specific issues I'm a bit of a noob.

I have a F-100, my mechanics book says "minimum compression" should be 90 psi. I checked it last night and only get about 45 on my guage. :(

The piston dosn't appear to be scored much from what I can see thru the exhaust ports, I just haven't cracked it all the way apart as I don't have parts yet anyway. On 2 strokes are the rings, piston, cylinder about the only factor in compression?

I got the mower from a yard sale, never put fuel in it, it needed attention before it could be ran. The engine spins fine, dosn't feel rough or like it had been partly seized at any time. Pretty tight on the crankshaft end play top and bottom. I just don't want to bother putting it all back together and making it nice if it's going to have no power in the end...

Secondary question: Do you guys that rebuild engines use any sort of piston stop in the spark plug hole when reassembling, or do you just be really careful to not slide the piston in to far? I haven't been able to locate one of the "special tools" that LB has, or just make something of my own?
 

·
nothing of interest
Joined
·
1,025 Posts
Put the piston in the jug shallow, put the rod on the crank shaft, that way the piston can't go into the cylinder too deep. Push the piston the rest of the way in.
I got one started on 62 pounds.
Ron
 

·
Lifetime Lawn Guy
Joined
·
1,426 Posts
Discussion Starter · #4 ·
ok, thanks. I was thinking stuck, or at least hoping that was the only issue (still hoping) but it will get new rings either way. Since it hasn't been ran in who knows how many years the rings may have stuck just from lack of use or lubrication in the cylinder.

I just didn't know if that was the only real factor in compression in a 2 stroke. In a 4 stroke there's a number of things that can cause loss of compression. (i believe).

Do most people hone their cylinders prior to reassembly? Or is that just total overkill? I'm talking about one of the simple kinds that just attaches to a drill, assuming one small enough can be found?
 

·
5K Poster!!!
Joined
·
5,142 Posts
Well, if your a hillbilly like me you can make one from an old spark plug with the porcelain broken out, drilled and weld a nut on it and run a threaded bolt through it.

I use it on my VW to find true TDC but also serves as an adjustable piston stop.


Its not to easy on the eyes but here it is.....
 

·
Lifetime Lawn Guy
Joined
·
1,426 Posts
Discussion Starter · #6 ·
Indy: That's kinda what I was thinking of... And I doubt if I made one it would be better looking than that! Function over form.
 

·
5K Poster!!!
Joined
·
5,142 Posts
Indy: That's kinda what I was thinking of... And I doubt if I made one it would be better looking than that! Function over form.
I hope your kidding.....I almost didn't post a pic because its not the best weld I've ever struck....I am embarrassed but it does work and saved me some $.

As for the compression and rings you can break them loose by simply using seafoam at 2oz per gallon fuel for one mowing season. Seafoam over a relatively short time will loosen the carbon deposits stuck in the ring grooves and get your rings springy again and raise your compression and power.
 

·
Premium Member
Joined
·
5,747 Posts
Add some oil to the cylinder to get it running then you'll see what you have. It may not require any attention at all after a short run.
 

·
Registered
Joined
·
4,418 Posts
Neal, dont be embarrassed to post that picture, I can tell it works well.. That is what i planned on making one of these days before you posted the picture. Sure it doesnt look great, but if it works good and gets the job done, that is what matters...
 

·
Registered
Joined
·
283 Posts
Well, if your a hillbilly like me you can make one from an old spark plug with the porcelain broken out, drilled and weld a nut on it and run a threaded bolt through it.

I use it on my VW to find true TDC but also serves as an adjustable piston stop.


Its not to easy on the eyes but here it is.....
HA! You should see the one I made for piston installation.

 

·
Lifetime Lawn Guy
Joined
·
1,426 Posts
Discussion Starter · #12 ·
I hope your kidding.....I almost didn't post a pic because its not the best weld I've ever struck....I am embarrassed but it does work and saved me some $.

As for the compression and rings you can break them loose by simply using seafoam at 2oz per gallon fuel for one mowing season. Seafoam over a relatively short time will loosen the carbon deposits stuck in the ring grooves and get your rings springy again and raise your compression and power.
No, not kidding, I own a welder, wire and stick, and I'm about as much as a welder as I am a computer tech guy. I can make it work, but it's not going to be pretty... haha. It's pretty much what I had envisioned, taking an old plug and gutting it out.

I'm looking to get it in good working order on the first start, I don't plan on running it or mowing with it much at all really. the mower is totally town down, may as well put it back together with the needed parts replaced.

Just pulled everything off the deck tonight, ready to strip and paint. Should be a learning experience to see what takes the paint off the best but dosn't leave tons of scratches in the aluminium.
 

·
Registered
Joined
·
194 Posts
Good one. But I think one piece of soft rope should do the same thing.

Well, if your a hillbilly like me you can make one from an old spark plug with the porcelain broken out, drilled and weld a nut on it and run a threaded bolt through it.

I use it on my VW to find true TDC but also serves as an adjustable piston stop.


Its not to easy on the eyes but here it is.....
 

·
5K Poster!!!!
Joined
·
5,127 Posts
What exactly do the piston rings get caught on if it goes too far into the cylinder where you can't get it out?
The end of the steel cylinder sleeve. The sleeve is smaller in diameter than the cast aluminum and if the piston is pushed in to far the rings will expand and basically lock the piston above top dead center.
 

·
nothing of interest
Joined
·
1,025 Posts
The end of the steel cylinder sleeve. The sleeve is smaller in diameter than the cast aluminum and if the piston is pushed in to far the rings will expand and basically lock the piston above top dead center.
And if you do not remove the piston from the crank , it can not drop far enough into the cylinder to cause you any problems.
Ron
 

·
Lifetime Lawn Guy
Joined
·
1,426 Posts
Discussion Starter · #17 ·
And if you do not remove the piston from the crank , it can not drop far enough into the cylinder to cause you any problems.
Ron
Obviously the simple solution, lol. I think I'll go that route, don't have to fabricate or buy a thing!
 
1 - 17 of 17 Posts
Top