Most common air leak areas on a 372?

[kneedeepinsaws]

I know of the boot as it fails often.
Do the crank seals go bad often in these units?
I have a real nasty air leak, will do a vac test soon here to see where its coming from. But top end is new, bottom end is used and was not messed with..
just want to get an idea of what I may need to do. I dont have a case splitter... can the crank seals be replaced without splitting?

 

[Mattyo]

I don't even give these a 2nd thought....they get split. New bearings are cheap .... get nachi on eBay for about 6 bucks a shot. Gasket kit and seals isn't bad either. Don't forget the tiny o ring under the bushing on the pto side.

Most common cause of bad seals....bad bearings. Split it clean everything. Test when back together.

 

[Bjorn]

 

[brad ruch]

I know of the boot as it fails often.
Do the crank seals go bad often in these units?
I have a real nasty air leak, will do a vac test soon here to see where its coming from. But top end is new, bottom end is used and was not messed with..
just want to get an idea of what I may need to do. I dont have a case splitter... can the crank seals be replaced without splitting?

Yes they can without splitting the case.i would bet it's the clutch side.everyone I've had with a leak was clutch side.but usally is the cause of a bad bearing or a clutch getting hot.

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[kneedeepinsaws]

Thanks guys ill check this out hopefully tonight with the mightyvac.
Is it common for air leaks to develop only when the saw is hot?

 

[brad ruch]

Thanks guys ill check this out hopefully tonight with the mightyvac.
Is it common for air leaks to develop only when the saw is hot?

Nope

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[Duce]

Are you buying am intake boots?

 

[kneedeepinsaws]

No i bought an oem boot, i watch afleetcommand YouTube vids sometimes and he says stick with oem for the boot. I figure hes done hundreds of saws so ill take that advice.

saw is surging on idle no matter how rich i turn the jet out and compensate with the idle screw. It has an unlim coil so its not timing advance for easier starting like the oem coil...
Hopefully the mightyvac will find the culprit. Gonna pull the flywheel as well and check those areas with soap.

 

[brad ruch]

You can also get it running and take a can of brake cleaner and spray it at the flywheel side and clutch side on the intake boot.if there's a leak the saw will quit.

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[David Young]

maybe a video of the problem would help us give suggestions

another possibility is the main jet leaking in the carb causing a funky idle

 

[angelo c]

maybe a video of the problem would help us give suggestions

another possibility is the main jet leaking in the carb causing a funky idle

ethanol carb probs are SOOOOO much fun eh?

 

[Czed]

I've had a few with intake tract leaks
So I motoseal the boot
Carb and cylinder side.
If the bearings are good i just throw some am seals in
I've used dozens no failures.
If bearings are needed Nachi are my favorite am bearings.

 

[Mattyo]

Again....I wouldn't even spend an millisecond of time testing at this point. By the time you are set up for a test you can get it torn down I've found it takes less time to split it than it does to set up for a test and then find out you need to split it anyway. Best of luck whatever u do. Feel free to check my vids for info and post questions here.

 

[Mattyo]

Btw...I like the brake cleaner idea from Brad. That's quick and easy way to tell if you really have an air leak. Otherwise sometimes throwing a new oem carb at this is helpful as David Young mentioned. Still ...if the saw is an original edition 372 then its over 10 years old and its getting split for sure. If it's an xtorq then its still not a bad idea to split it.

 

[kneedeepinsaws]

maybe a video of the problem would help us give suggestions

another possibility is the main jet leaking in the carb causing a funky idle

Ok i will get one when i get home

 

[trooney]

Check the bushing on the clutch side also. Had one drive me crazy because I couldnt get it to seal up on that side. It was a tiny fracture in the bushing, so tiny couldnt see it with the naked eye. Put another new OEM one in there and it did the trick.

 

[kneedeepinsaws]

Check the bushing on the clutch side also. Had one drive me crazy because I couldnt get it to seal up on that side. It was a tiny fracture in the bushing, so tiny couldnt see it with the naked eye. Put another new OEM one in there and it did the trick.

Wow ok that sounds like something i would have def missed. I am almost home so a video will be up shortly.

what kind of ‘fracture’?
This surging idle issue has been happening for a while, i did a top end swap with new parts to find its running the same...
Either i did not seal up the base of the cylinder correctly botth times or something from the bottom end is leaking.
I really appreciate the help boys!

 

[trooney]

A little hairline crack. I inspected it many times and couldnt see anything. New seals and a new oring and it was leaking between the shaft and the seal. I thought it was the oring, went through about 3 of them. Then JJ suggested it might be the bushing even though I couldnt see anything. Got a new OEM bushing and that did the trick.

 

[kneedeepinsaws]

Here is a video. Shes not surging as much this time but idle is climbing then lowering.
I know something is wrong cause she dies after a throttle blip, and the idle screw has no effect unless full revolutions are made. On all my other saws the idle screw you just adjust it about 1/8 to get things right.

another thing is that just before that video was made, i was running it trying to get my phone in the right position and it stalled and a puff of blue smoke came out where i was spraying with carb cleaner! Lmao

I honestly am starting to think im putting the motoseal on way too thin...

I have ordered base gaskets from china, but who knows when they get here.
this week im going to order oil seals, and a new bushing (thanks trooney!!) and wait another two weeks for that to show up.. ordering online is the same wait time so id rather put my money in local business’s
In the meantime im gonna do a vac test and see whats going on here before i rip off the top end again.
Gonna wait for it to cool down and start rigging up the rubbers for the muffler and boot.

thanks again for helping me out, ive dumped so much money into this thing and i am certain i can only blame my inexperience.

 

[kneedeepinsaws]

Again....I wouldn't even spend an millisecond of time testing at this point. By the time you are set up for a test you can get it torn down I've found it takes less time to split it than it does to set up for a test and then find out you need to split it anyway. Best of luck whatever u do. Feel free to check my vids for info and post questions here.

Hey i appreciate your feedback. At this point i do not have a case splitter, its not an option right now. I am willing to buy one but i believe there are other tools that should be purchased as well? If you would be so kind as to suggest said tools to make this job as easy as possible for a mechanically inclined chainsaw amatuer that would be awesome

i have tested now and the clutch side is bleeding air without the clutch installed (see pic of bubbles). The o-ring is in there but unlike your video it will not seal unless the clutch is installed. with the clutch installed its holding pressure indefenitly. Is this an issue?
flywheel side has no issues...

i have an oring kit that is designed for AC systems (they are green) in which they are very resiliant to oil gas etc. They are very thin and similar to the husky one, im going to see if they are a fit...