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Leak down test.
Posted: Sat Apr 11, 2020 8:19 pm
by 10 inch Terror
Hi all, I’ve been tracking down a leak on an engine I built in 2016. I traced it to the M6 threads that hold the stator plate in the mag housing. I used a brand new new SIL housing along with a brand new SIL engine case. The bolts were very loose in the threads so I re tapped them and put new inserts in. This slowed the leak down but it still leaked slightly. I then smothered the threads with liquid gasket but it still leaked. In the end I wrapped PTFE tape around the bolts and I’ve managed to keep it at a solid 6psi. My question is, will the engine build up much more than 6psi and has anyone else used PTFE tape in the same way with any success? Basically will it be ok or am I heading for a blown engine a few miles down the road? Thanks in advance Pete.
Re: Leak down test.
Posted: Sat Apr 11, 2020 9:17 pm
by Muppet
Not all engines hold pressure all will leak pressure slowly; if it can hold pressure and not lose more than 1 psi per minute under a leak test it’ll be fine
Re: Leak down test.
Posted: Sun Apr 12, 2020 9:40 am
by coaster
Are you sure its not the mag housing gasket thats giving you the problem?
Re: Leak down test.
Posted: Sun Apr 12, 2020 12:58 pm
by 10 inch Terror
coaster wrote: ↑Sun Apr 12, 2020 9:40 am
Are you sure its not the mag housing gasket thats giving you the problem?
They are the only place bubbles appear when I spray soapy water on them. Everywhere else’s is bunged off and appear to be leak free. I could actually here the air escaping from them yesterday. Ive now got it to hold pressure for a certain time. For example if I pump it to 4psi it will take 5 odd minutes to drop to 3psi. Will this be ok? Thanks Pete.
Re: Leak down test.
Posted: Sun Apr 12, 2020 2:08 pm
by Muppet
dont take my word for it but motion pro know more than most
http://images.autodist.com/webattachmen ... tester.pdf
read it through and it answers your question
Re: Leak down test.
Posted: Sun Apr 12, 2020 2:43 pm
by 10 inch Terror
Good enough for me. Thanks Muppet.
Re: Leak down test.
Posted: Sun Apr 12, 2020 10:46 pm
by coaster
10 inch Terror wrote: ↑Sun Apr 12, 2020 12:58 pm
coaster wrote: ↑Sun Apr 12, 2020 9:40 am
Are you sure its not the mag housing gasket thats giving you the problem?
They are the only place bubbles appear when I spray soapy water on them. Everywhere else’s is bunged off and appear to be leak free. I could actually here the air escaping from them yesterday. Ive now got it to hold pressure for a certain time. For example if I pump it to 4psi it will take 5 odd minutes to drop to 3psi. Will this be ok? Thanks Pete.
The stud holes shouldnt be open to the crankcase so I was thinking that maybe the flange gasket was leaking from the crank case to the stud holes?
Glad to hear that leakage of 1psi pm is ok as I dont think Ive ever managed better than that. Usually there is some leakage arounf the exhaust flange which Im happy to accept as you can never get a seal on the slip joint once you are using it on the road.
Re: Leak down test.
Posted: Mon Apr 13, 2020 1:08 pm
by 10 inch Terror
If I pump it up to 4psi it takes almost 3 minutes to lose 1psi. That’s probably as good as I’ll get it and well over the 1 minute per psi allowance. Thanks all.