Thinking of Rebuilding my Jonsered

[kd460]

It's a 510sp. I bought it used about a year ago. It always starts within 3 or 4 pulls cold (even weeks) and 1 or 2 when warm. Cuts good, seems to have plenty of power, for what I paid, I feel I got a descent saw. I have no problem using it the way it is.

Got bored the other day and decided to check compression and look inside exhaust port. Compression reads 70psi cold (does that seem right? this thing cuts and runs well! I used an automotive compression gauge) It has some vertical lines (nothing deep but can see a few) in the cylinder and on the piston skirt some look deeper.

I don't have any unrealistic expectations with this saw. I used it hard this past year and it owes me nothing. But,was thinking of making a project out of it and doing a rebuild. I contacted George Blake and he is looking into parts. I have the parts diagram and the factory service manual. I have rebuilt car engines and motorcycle engines, but this will be my first saw. I was up front with George and told him if the $$ is to much, I'll just leave well enough alone and maybe get a new saw.

Not ready to tear this one apart yet. Still waiting on parts availibility (if still available). I'm still playing with the idea of a rebuild. If no more parts, then decision is already made for me. Just curious from you rebuilders if honing is an option, is oversized pistons and rings an option (or is this even done on chainsaws?) or is a new cylinder, piston, ring, needed with every rebuild?

I suppose if I am in it, I should replace crank bearings and seals. Anything else? Small end conn. rod bearing?

If it cuts this well with 70 psi compression, I'm sure I'll be impressed when (and if) rebuilt. Thanks, KD

 

[TimberPig]

Since it cuts and runs well, I'd suggest you get a proper compression tester. Evidently your autmotive gauge doesn't have the proper Shrader valve required for correct readings on small engines. A saw with only 70 psi will not start and run well. Your saw's compression is much higher than that. You'll likely find the reading is so much higher, a rebuild isn't really needed yet. If the saw runs and cuts well, like you say, it probably doesn't need a rebuild.

 

[sawinredneck]

Pull the muffler and have a look before you tear into it at all!!! Doesn't sound right to me either!
Andy

 

[manual]

It's a 510sp. I bought it used about a year ago. It always starts within 3 or 4 pulls cold (even weeks) and 1 or 2 when warm. Cuts good, seems to have plenty of power, for what I paid, I feel I got a descent saw. I have no problem using it the way it is.

Got bored the other day and decided to check compression and look inside exhaust port. Compression reads 70psi cold (does that seem right? this thing cuts and runs well! I used an automotive compression gauge) It has some vertical lines (nothing deep but can see a few) in the cylinder and on the piston skirt some look deeper.

I don't have any unrealistic expectations with this saw. I used it hard this past year and it owes me nothing. But,was thinking of making a project out of it and doing a rebuild. I contacted George Blake and he is looking into parts. I have the parts diagram and the factory service manual. I have rebuilt car engines and motorcycle engines, but this will be my first saw. I was up front with George and told him if the $$ is to much, I'll just leave well enough alone and maybe get a new saw.

Not ready to tear this one apart yet. Still waiting on parts availibility (if still available). I'm still playing with the idea of a rebuild. If no more parts, then decision is already made for me. Just curious from you rebuilders if honing is an option, is oversized pistons and rings an option (or is this even done on chainsaws?) or is a new cylinder, piston, ring, needed with every rebuild?

I suppose if I am in it, I should replace crank bearings and seals. Anything else? Small end conn. rod bearing?

If it cuts this well with 70 psi compression, I'm sure I'll be impressed when (and if) rebuilt. Thanks, KD

If it works don't fix It. So the saying goes.

Now if you think you have low compression , I would first check it with a different tester and or use your tester on an other saw.
If your mind is set on preventive maintenance, You would most likely need a new set of rings. for starters.
sounds like you want to see how your saw ticks, so go ahead and pull the jug you can get a better look at it that way anyway.
Plus it gives you a chance to clean all the carbon deposits. Its not like you are dealing with a new saw.
So now were talking rings , cylinder gasket, intake gasket.
Hows about taking a pic of the cylinder when you get it torn that way we could guide you better on you project.

Have fun and talk to ya later.

 

[SmokinDodge]

OK, kinda hillbilly but it works, with only 70 #'s of compression you should be able to hold the starter handle and let the saw drop and it should just about FALL to the end of the rope. A good running saw (high compression) will slowly decend usually pausing near the top of the stroke. Give this a try with the switch in the OFF position and see what she does. I'm betting you just need to get the correct comp tester.

 

[gene1605]

piston rings

If you replace the rings before you start to loose compresion you will eliminate excesive cylender wear.
grampa

 

[kd460]

OK, thanks. Yes, I like the "if it ain't broke" philosophy. As a matter of fact, I read that allot when I searched other rebuilding threads.

I'm glad you guys mentioned the possible problem with compression gauge. I started to think that myself. I checked the gauge with a newer string trimmer and it reads 60 psi cold. So, time to get a compression gauge for small engines?

I also did the "drop test". It chugged to the ground slowly, grabbing at each compression stroke. Kind of awkward to do with the bar is still on.

Tonight I'll pull the muffler and try to get a pic of the scoring I mentioned earlier. Yes there is some carbon around the exhaust port. But not bad.

OK, so feeling better about the saw not being as whipped as I thought. Was kind of looking forward to rebuilding it, as well as a good excuse for a new saw.

I'll post pics this eve. KD

 

[kd460]

Attempting to post pic:

http://www1.snapfish.com/slideshow/...ID=2671285358/a=84398092_84398092/t_=84398092


OK, finally got the link to work. Not sure how you get photos to show up in a post. Anyways, heres a link to the pics of piston and cylinder wall. Normally it is not wet like in the pic. It's from doing the drop test.

Also shining a light into the port makes the wear look worse than it is. KD

OK, looks like only one pic came thru. Screw this. KD

 

[ericjeeper]

Run it

looks like it has lots of life left in it.