Handicapped or blessed ......... even a combination of them, you did a fantastic job. What I am really looking forward to is the fact that you could easily cut another cap and swap out the stuffed one to see what difference those 3D inventions make. I love the timing charts you do !!The 3D printer is about the only "high tech" equipment I do have access to. Other than that it an old worn out lathe driven by a leather belt, some drill presses and belt sanders. The CNC stuff is all set up for production work and I don't know how to use it anyway (although I have been considering learning to program one). And a Dremel.
Do you know what the squish is? These engines are easy to pull over stock, so maybe it is not a sign of a problem with the piston/cylinder.OK, Chris, I'll double check all of that. But, I think that's what I already did in November. Compression still seems nil compared to any Stihl that I own, and that's usually the bottom line. I was very careful when rebuilding the top end and saw no difference in rope pull resistance after completing it. Not much is more depressing than that. I'll report back what I find and show you a Pic of the piston before I started.
OK, I'm all ears. After installing a new piston and rings (saw looked like it was straight-gassed), it still seems to have insufficient compression to start, even with a good spark and carb settings as recommended. Saw has very few hours on it and looks brand new. My Stihl dealer told me to stop wasting my time on junk. What's next for me to try?
Doc,
will it fire if you force feed a few drops down the exhaust or intake ? should still pop and fire somewhat uncontrolled.
Absotively , my assumption was he confirmed spark and was concerned for compression. If it won't fire with known spark well then it can only be "timing" or compression.Not if he isnt getting spark
Soon we'll be complaining about the heat and ticks.... !!!Sitting here at work wishing I was home and the ground & wood were not covered with snow so I could try that saw out for real.
And mud.Soon we'll be complaining about the heat and ticks.... !!!
What is that that "-" symbol in front of the number 18? That's a bad thing, right?heat ticks and mud all sound wonderful this weather is really getting me down...........
View attachment 406418
Hey, I see some wood sticking out there - enough to run a saw in for a few minutes anyway!
Sure thing...come and join me. Bring some saws. I got a few we can run too.What is that that "-" symbol in front of the number 18? That's a bad thing, right?
Hey, I see some wood sticking out there - enough to run a saw in for a few minutes anyway!
Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.Doc,
will it fire if you force feed a few drops down the exhaust or intake ? should still pop and fire somewhat uncontrolled.
Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.
Is it worth removing the cylinder again? How could there be practically no compression at all? I've never seen anything like this.
Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.
Is it worth removing the cylinder again? How could there be practically no compression at all? I've never seen anything like this.
Great job. Did you use 4047 filler rod?i recently done up a MS390. being a clamshell. i went the easiest option to boost the comp.
tried this but fouled.. so got a stock piston and with the aid of Plasticine, got am imprint from the combustion chamber along with the plug in!
ended up with something similar to this . and ended up with 185 psi. all standard port timing as nothing else was changed.
OK, I'll back out. I took it apart again and found the problem. A chunk of the lower right rear (carb side) corner of the cylinder broke off. It must have had a hairline crack in it that I didn't see when I installed the new piston and ring. Funny thing also, the piston ring was broken, even though the saw never started and ran after I installed it. Anyway, at least we now know why there was no compression.Doc,
It's got to be leaking somewhere. Spark plug, case fittings, seals ect. can you add some pressure and hunt down the leak. Maybe start another thread and keep Chris's focused on hotrodding a clam. lets get yers runnin then have Chris turn up the volume !!!
The castings are quite nice on these - remember, the only machining that gets done is the bore and the spark plug hole. The rest must be accurate enough to use without machining, so it can't be junk. I'm not sure what happened on yours, but I've never had one break - just the typical scoring and stuff.Are you guys sure that these saws are built well enough and tough enough to hot rod them?
Oh yes. I think the guys had a wild thing build off a couple years ago. The ones that lost the competition were amazing. The winner was unbelievable in the power it put out. This is Masterminds saw. Seems to run pretty well even with the air leak.
Enter your email address to join: