Pressure/Vacuum Testing the MS460...problems

I rarely post questions, but AS isn't what it used to be and all the old (see: lakeside) threads don't have pics.
I got some interesting results from my first pressure/vacuum tests on my MS460. For starters, it didn't have any running/idling issues. I got a p/v kit from a retired stihl dealer and wanted to try it out.



Pressure-
Started at .5bar... then went down!
down to .4bar at 26seconds
down to .3bar at 59seconds
down to .2bar at 1:59

Vacuum-
Started at .5bar... then went up.
up to .4bar at 30seconds
up to .3bar at 1:08
up to .2bar at 1:56

Per the manual, that .5bar should have held steady for 20seconds. Per old threads, it's possible to lose a little pressure but not have an issue. The vacuum leak was within the manual's "rising to no more than .3bar within 20seconds"
So... did it fail both tests? I sprayed windex and soapy water at the cylinder base, plug hole, and case gasket. I only got a couple tiny bubbles near the plug, but I don't think that was it. I plugged the decomp hole.
This saw got all new rubbers, case split w/ new bearings, and new seals.
Funny thing, I can tune it perfectly and it holds idle at 2500rpm.

 

Here are the other materials needed for this test. It's possible to use rubber from an old inner tube (or similar material) to plug both intake and exhaust. Then, the impulse line is used to deliver pressure/vacuum. I used the muffler itself to block the exhaust and then tried a bunch of gaskets and the heat shield... worked ok but I imagine using a block of steel is a better way to go. It's also possible to just vacuum test using this:

 

Oh yeah... almost forgot. Here she is- picked up as a basket case for $100. Needed new bearings and had a catastrophic p/c failure (broken transfer bridge and scored it up a bit... no Al transfer, tho). Used a cylinder from the scrap bin after cleaning it up with emery and sandpaper. Blows 165psi and is a good runner-

 

Submerge it under water with 10psi on it constant. U will find the leak. My 026 I just finished held 13" vaccum for 2 days

 

Don't forget that leaks along the tester hose itself can cause this. Did you check for bubbles at the point where the pressure tester connected to the saw, and the temporary seals you established at the intake and exhaust? Barring a fractured case or cylinder head, the only other potential leak points would be the crank seals, intake manifold and impulse hose.

 

I just got back from checking the tester itself... I was down there working when you guys typed out these ideas haha. I decided to check out the tester on a known kick-A saw (my 034Hybrid). After spraying the entire hose and tester down with windex, I found a massive leak right at the connector! The Al flange and nipple is leaking and giving me false readings. The 036 flange held better than the 460, but both had the same issue. The only other leak I found was a small bubble near where I am blocking the exhaust.
Either way, there's no bubbles around the cylinder base, intake book, and hose. I didn't want to pull the flywheel/clutch quite yet but I did spray some windex on the crank and around the flywheel (don't know if that'd show anything, but who knows). I'm pretty sure the saw(s) are tight, so it's time to fix the connector flange.
Thanks for the help guys!

 

Certainly sounds like you found the culprit(s), but you should always check the testers themselves in terms of the valves & mechanisms. I bought a brand new Stihl test kit from a guy that went out of business and had an extra. I had done probably less than 50 tests when the pressure tester went bad and within another 25 or so the vacuum tester ceased working as well. Beat my head on the bench for a couple of days trying to figure out where the leaks were coming from before it occurred to me that the inner seals/valves of the testers were causing the issues...

 

Makes sense, NewToStihl... I'm sure that this stuff wasn't used too much and probably hasn't been used in 10 years. I got the entire kit for $65, so it wouldn't be a big deal if there were more issues with the actual valves and mechanisms. Hopefully it's just the test flanges and nothing else. My finger can hold pressure/vacuum all day, so the testers check out for now haha.

 

Thoughts on what sealant to use around the test flange? It's where the nipple goes into the flange itself. I have RTV, Loctite 518 (needs absence of air to cure, right?), permatex gasket maker, and assorted other sealers.

 

I can't help you but I would think any RTV silicone would be fine.

I am hoping to perform my first pressure/vac test in the near future.

Very nice rebuild!

 

Thanks, man. It was quite the experience. I should have done a rebuild thread on it but I encountered so many issues it would have been pretty boring and spanned about two months haha.

 

Here's the thing, you just would have accumulated more popcorn eaters.

It seems like FHC has quite the range of experience. When someone takes time for the newbies, it gives the newbies confidence or desire to tackle the next thing. You get a few saws under your belt and the newbies can answer some questions too now.

What are your plans for the 460?

 

Try teflon tape ,yellow for natural gas, around the threads.

 

I thought about taping things up tighter but wasn't sure which tape to try... good idea using the yellow tape, thanks KRL!

As for the 460, it'll be added to my lineup for bigger stuff. I have a 20" b/c ready for it as needed, but I think I'll keep the 28" on it most of the time.