372 Acting Lean

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

quincyhoke

ArboristSite Lurker
Joined
Apr 17, 2014
Messages
30
Reaction score
11
Location
Northern CA
Please bear with me as there is some background to this issue.
372XP XT

I used the saw to clear a few trees out of the road one day, went through half a tank of fuel probably. I shut the saw off for a couple hours, fired it up again and idle was high with moderate chain spin. I ran it for about 3 minutes and shut it off. I took everything off and found one of the head bolts had backed out and gas was leaking between the jug and the case. I pulled everything, piston and jug looked fine. Threw new rings in and bolted it back together.

I'm still having the idle problem. Adjusting the idle and L screw in combo to bring the saw to low enough idle yields minimal throttle response and the idle is a mildly erratic.

The problem was instant the last time it fired up. Didn't add fuel or touch anything to cause the issue. Ideas at this point are possibly a carb problem or maybe an air leak at a bearing?? Both ideas don't seem to fit the timing of the issue. I'm at a loss.
 
Did you look at case bearings, vacuum check case, replace impulse line (had a problem with few being loose fitting)?
 
Did you look at case bearings, vacuum check case, replace impulse line (had a problem with few being loose fitting)?

I hadn't thought of the impulse line. I don't have a system to check vacuum an I didn't tear it down far enough to really get to the case bearings. Maybe I'll just have to take it in to get a vacuum test.
 
I hadn't thought of the impulse line. I don't have a system to check vacuum an I didn't tear it down far enough to really get to the case bearings. Maybe I'll just have to take it in to get a vacuum test.
Where in NoCal are you? If near enough to Napa, I can give you a hand with a vacuum/pressure test.
 
Sounds like you have a air leak someplace, compression release can sometimes be a source, I usually re tighten the cylinder a muffler bolts after the first run after it's been used enough to get warmed up and sat for a while but all and all a vac-pressure test will tell the story, seals are easy to replace on those saws and the oil pump screws holes go right through into the crankcase so I use some red silicone high heat to put on those threads when assembling, my little Mityvac was one of the best tool investments I made for diagnosing problems.
 
I went ahead and was going to replace the crank seals just as a trial. An old mechanic once told me seals don't go bad by themselves ad that was the case here. Looks like it will be getting some new crank bearings as well.
 
If you don't have a vacuum pump you can spray a little carb or brake cleaner around the seals, base of the cylinder and carb boot. If you get a change in rpm you found your leak. You could also go to your local auto parts store if they have loaner tools and get a brake bleeder kit and a vacuum gauge and use that to do a vacuum test.
 
I went ahead and was going to replace the crank seals just as a trial. An old mechanic once told me seals don't go bad by themselves ad that was the case here. Looks like it will be getting some new crank bearings as well.
At least those bearings are on the inexpensive side. Check out "shorenutz" on Ebay for a good price on Nachi C3s
 
I would be finding that leak or ruling a leak out before I went through the trouble of splitting the cases and installing new bearings unless you already know they are bad. I could be something as simple as a cracked boot or one of the new seals leaking. When you replaced the seals did you put a new o ring on the clutch side?
 
I would be finding that leak or ruling a leak out before I went through the trouble of splitting the cases and installing new bearings unless you already know they are bad. I could be something as simple as a cracked boot or one of the new seals leaking. When you replaced the seals did you put a new o ring on the clutch side?
I didn't even make it to the new seals. I pulling the clutch side and found that side of the crank is sloppy. Checked the flywheel side also and it felt decently tight.
 
Any play in that crank as in any vertical movement at all and the bearings are on their way out.
This usually happens due to contaminants getting in either through the air leak or an air filter that has a hole in it, not tight enough or way too dirty.
Either way you gotta split the cases to fix that problem, I would do this and start going through all the parts before you order anything. A lot of times you will find more that needs to be replaced when you tear it down.

Good luck :)
 
And don't assume that the clutch side bearing seat isn't damaged. Enough vibration to loosen a cylinder bolt could indicate that the outer race has been spinning/rattling in the housing.

If this happens to be the case, can I just ping that bearing seat and set the bearing as usual?


Any play in that crank as in any vertical movement at all and the bearings are on their way out.
This usually happens due to contaminants getting in either through the air leak or an air filter that has a hole in it, not tight enough or way too dirty.
Either way you gotta split the cases to fix that problem, I would do this and start going through all the parts before you order anything. A lot of times you will find more that needs to be replaced when you tear it down.

Good luck :)

Thanks for that. That bearing does have minimal vertical play but has significant horizontal play(maybe 1/4" total). What is the reason that primarily vertical play should be assessed?
I'm in the middle of a Toyota engine rebuild at the moment and know about the additional parts thing.
 
Sounds like the bearing cage is no more and all the bearings drop to one side, not necessarily spun your case but you won't find out until you split the cases and hopefully what was left of the cages didn't do any damage to your cylinder or anything else, you might have to space the balls in order to get the old bearing out or off, a saw like that is one of the easiest saws to work on and parts are easy to find.
 
If "ping" is to ditch, chuck or throw away...no.
If the bearing just drops in or is easily pushed in when the case is at room temperature, it and/or the case won't last long.

What I meant by pinging is using a center punch in multiple places along the bearing seat to deform/displace some metal, not getting rid of it.
 
Husky used a real thin O ring over the crank on the oil pump side, so dont go without. Did you notice it in there? One of the Husky guys should be able to give you a part no. The O ring was about a small air leak on the pto side.

Also when replacing bearings, replace the seals at the same time. Do these in pairs. If the bearing pocket is loose, use bearing set.
 
Back
Top