Thanks. Have always checked both but never focused on the sequence as being critical. I think we have confirmed the saw holds vacuum and pressure.
Blown 661...again
- Thread starter angelo c
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Yes. I don't understand your point. And I also don't understand why so high of a vacuum is needed when a saw normally runs at 5-10 in.
The bottom line is the saw holds pressure and vacuum while static and rotating the crank.
You using a mityvac?
Yes. 8500
Right, then I recommend you do as I suggest when testing vacuum, because if you don’t you’re not testing it correctly.
If you’re pulling a vacuum up to 5 (which reads in inches of Mercury) on vacuum, you’re pulling just over 2psi… that’s way to low. There are roughly 2 inches of Mercury to 1 psi.
You should be pulling a minimum vacuum of around 16, ideally 20 inches of mercury which equates to 8-10 psi, then start rotating the crankshaft 5-10 times.
Copy.
Never really looked that closely at the 8500 dial. Just looked for "10"
Thanks.
Never really looked that closely at the 8500 dial. Just looked for "10"
Thanks.
Vac will test a seal where it seals on the crank itself because pressure will push the seal closed on the inner lip ! I have seen them pass pressure, but vac failed. Vintage Engines offered good advice. Dmb said he would like to see the piston, so would I. Pics?
when you pull the cylinder off I would like to see pics of the piston side and top
Intake correct ?
both sides and top
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- May 13, 2014
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The Stihl service manual outlines how to test seals, what order, and the vac/pressures to use. I suggest giving it a read. Vintage is correct so I also suggest following his suggestions and re testing for leaks.
Also, echoing several prior requests for photos of the piston with the cylinder removed.
Very knowledgeable folks here and you are being resistant to their feedback and light on details. For example it required several posts to figure out the year of the saw, which mtronic it has, and what you already tried.
"Help me... help you" as Jerry Maguire said.
Also, echoing several prior requests for photos of the piston with the cylinder removed.
Very knowledgeable folks here and you are being resistant to their feedback and light on details. For example it required several posts to figure out the year of the saw, which mtronic it has, and what you already tried.
"Help me... help you" as Jerry Maguire said.
Is that just RTV sealing the cylinder or a proper fuel rated sealant?
That's not my expiereance.
Isn't that a metal gasket in there too?
Don't pull it until you pressure and vac test it.
You guys realize that Dirko is silicone, correct?
Never met Angelo, but I know him. Been in group convos with him for a couple years. He’s not inexperienced at this. It would be nice to see some help offered instead of going in raw like he’s a newb with no idea.
As far as the p/v test, I agree with the vac first. But I’ve learned on my own time that seal issues that affect running characteristics are instantly noticeable on the needle. If it holds 7 on the vac or pressure side without falling off while you rotate the crank, it’s not an air leak that’s causing the issue. There’s no way in hell that a hairline leak at + or - 10 psi, but no leak at + or -5 psi is going to score a cylinder. At 10k rpm there isn’t time for that kind of pressure differential to happen on every revolution anyway. You’re talking 2-3psi each way from 0 max
Never met Angelo, but I know him. Been in group convos with him for a couple years. He’s not inexperienced at this. It would be nice to see some help offered instead of going in raw like he’s a newb with no idea.
As far as the p/v test, I agree with the vac first. But I’ve learned on my own time that seal issues that affect running characteristics are instantly noticeable on the needle. If it holds 7 on the vac or pressure side without falling off while you rotate the crank, it’s not an air leak that’s causing the issue. There’s no way in hell that a hairline leak at + or - 10 psi, but no leak at + or -5 psi is going to score a cylinder. At 10k rpm there isn’t time for that kind of pressure differential to happen on every revolution anyway. You’re talking 2-3psi each way from 0 max
I am aware that Dirko is silicone and I wouldn't use it for that reason. I had a failure with a silicone based Threebond product years ago and vowed to never use silicone anything again.
