Low Compression

[saxman]

I have been offered a saw that cranks freely but won't start. I was told it has low compression. I am no chainsaw mechanic but for the price I am tempted to take it and teach myself the basics. With a two cycle engine I presume the reason for low compression is rings/scored cylinder walls. If this was caused by lack of lubrication would not the bearings/crank be damaged as well? Are there any other reasons for low compression other than what I have listed? Thanks for you help.

 

[Simonizer]

I have been offered a saw that cranks freely but won't start. I was told it has low compression. I am no chainsaw mechanic but for the price I am tempted to take it and teach myself the basics. With a two cycle engine I presume the reason for low compression is rings/scored cylinder walls. If this was caused by lack of lubrication would not the bearings/crank be damaged as well? Are there any other reasons for low compression other than what I have listed? Thanks for you help.

Faulty decompression valve (if it has one). This is rare. I think your problem is a scored cylinder/piston.

Pull the spark plug out and shine a small Mag-lite or equivalent against the cylinder wall on the exhaust side. You may see the failure immediately.

 

[Fish]

What price, and what brand/model is it?

 

[Simonizer]

There is something fishy going on here.

 

[Fish]

Not yet, sweet pea.

 

[Simonizer]

Not yet, sweet pea.

The sucrose level of my urine is not important right now.

I have a Simonized 385 XP in my living room. Brand new. I am taking some pics but am a little reluctant to show exact porting work. I think I should offer to show one of the ports, stock vs. modified. I have been advised by some of the techs at work to be careful about revealing too much info. Your thoughts?

 

[Fish]

Yeah, I would be reluctant to lay out your work in too much detail.

I believe that you are likely quite skilled at what you do, which is not in my field. I specialize in making the saw run like it did when new, sometimes better. Since my
average customer would not know the difference, I leave the modifying skills to those
in timber country, but just cause trouble here for the hell of it.
I am a chainsaw harpie, just keeping the pot stirred enough to justify my massive
Arboristsite stipend.
Of course my "Fisherized" Eager Beaver, with the patented "Maglev" bar chain
system is quite real, and of course for sale.

But for liability reasons, the sales must be cash only, as these poor fools do not know how to mix liquid nitrogen with my "Synthetic" bar oil.
I am working on using the intenz bar, as the liquid nitrogen mix, might keep the
chain tight, then Oregon will have to fork over some cash for my help.
The Oregon dude has not been too much help here, as he just hates my fat butt.

 

[Fish]

Actually, by the time it passes the bladder, it would be glucose

 

[Fish]

Well before that.

 

[Simonizer]

Actually, by the time it passes the bladder, it would be glucose

Alas, it has not passed yet. I remember playing with liquid nitrogen in the physics lab at UBC. It is as cheap as milk. When it is at 77K it is very comfortable to live in a high quality thermos. I did all the stupid experiments you could think of with it. I did some cryogenic experiments with it, trying to improve results of the "hall effect" etc. and accurately measure drift currents. I achieved "A" marks throughout my engineering degree but wasn't imaginative enough to do any ground-breaking research. The most important lesson I learned was that no matter how brilliant you think you are, there is always someone who can bury you on a give topic. I went to MIT for my masters degree on a scholarship. I arrived thinking I would own the place. I was mistaken. I was mid-pack. Stupid Americans were smarter than I had anticipated. I was lucky enough to attend a lecture by the late Richard Feynman at Cal-Tech one September, that is when I discovered I had a lot to learn.

 

[Fish]

Heck, you just got excited because you thought I said hairpie!


During college, I was torn. I went in with a serious religous thing going on,
a serious teenage lazy/party thing going on, and a healthy curiousity about science.
Of course hotlegs and wet t-shirt contests muddied my perspective as well.

Unfortunately, I focused on the teenage lazy/party thing, and the wet t-shirt thing was involved as well.

 

[Simonizer]

Heck, you just got excited because you thought I said hairpie!


During college, I was torn. I went in with a serious religous thing going on,
a serious teenage lazy/party thing going on, and a healthy curiousity about science.
Of course hotlegs and wet t-shirt contests muddied my perspective as well.

Unfortunately, I focused on the teenage lazy/party thing, and the wet t-shirt thing was involved as well.

Hair-pie, yikes. That went out in the late 80's (thankfully).

 

[saxman]

Back to my original question, what are the chances that the bearings are damaged?

 

[Simonizer]

Back to my original question, what are the chances that the bearings are damaged?

Excellent. (Con-rod bearings) If they have a mirror-like finish, they are OK. Sorry about de-railing your thread buddy.

 

[saxman]

No Problem, so you think they will be damaged or not?

 

[Simonizer]

No Problem, so you think they will be damaged or not?

They may be damaged. If they have a mirror-like finish, they are OK.

 

[saxman]

10-4, thanks alot

 

[Fish]

Actually, they are likely fine, back to the original thread.
What make/model?

Price?

 

[Al Smith]

The original question was if low comp will prevent starting,likely not but it wouldn't run very well.

 

[saxman]

It is a shindaiwa 500. I have a shindaiwa 350 that I really like. The 500 was the biggest horizontal saw that they made. This will be a learning project for me as I have never torn a saw engine down. I have a MS260 and a 044 as well. Any pointers from anybody? I presume I will have to replace the jug and piston.