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Do I need to do a Leak Down Test?

cowboyup3371

cowboyup3371

Forum Guru
Past Site Supporter
I didn't find anything in the service manual but I have read up on others here on the board who did it so I'm not sure of the proper protocol. Do I need to perform a leak down test of my valves once I put everything back together? Or is it only something I do if I find a problem afterwards?

What's the right way to do it?
 
Did you disassemble the head? and if you did, were the valves lapped? If you lapped the valves and the contact surfaces between valve and head looked good, then no, there is no real need to do a leak down test.

Now if you didn't have any history on the bike, or you didn't check the contact surfaces when reassembling the head after any major work like valve replacement, then either a compression test or a leak down test might be a good idea at this point before you slap everything back together.
 
The next question is, do you or have access to either a compression tester or a leak down tester?
 
Yes everything came apart and Steve and I lapped the valves (see my project thread). I also looked at the surfaces and cleaned everything up in the parts washer. As I'm still waiting on a few o-rings I forgot to order, the head isn't reassembled yet but should be in the next couple of weeks. That will give me time to go through things again.

I personally don't have a tester but it won't be too hard to obtain one if needed as I think the friend whose garage I'm working in might have one.
 
I've seen people flip the head over and put kerosene/gasoline/whatever in the valve dome area and let it sit for a while. If they don't leak much (or at all), then it's good.

Again, don't know if it's an accurate test but I've seen it done.
 
You can Google leak down test and see units, procedures and even videos on how to do it.
I have a commercial one at home if you can't find one locally.
 
eil said:
I've seen people flip the head over and put kerosene/gasoline/whatever in the valve dome area and let it sit for a while. If they don't leak much (or at all), then it's good.

Again, don't know if it's an accurate test but I've seen it done.
Click to expand...

I do this too. The service manual for the 1100 says to pour some gas (I use rubbing alcohol as the fumes are not as noxious as gas fumes are to me) into each port and check for leakage around the valve seats. Even though I had my valve job done on a Serdi machine I still had some seats leaking. So I hand lapped those leaking seats with fine compound until I had zero leakage on those seats.

As for Leakdown tests I am a big believer in them. But a simple compression test is fine too as a starting point. If your compression test results are pretty much even across the board and with in specs than you don't really need to do a Leakdown test. However, if your compression test reveals a low cylinder than a Leakdown test is an excellent diagnostic tool that will reveal where the loss of compression is coming from.
 
you'll never get another chance to make sure the valves don't leak.
level the head, pour gas or kerosene in the chambers and wait 10 minutes
A tiny seep is ok, if the chambers empty out there is a problem/
 
A regular compression test is first, if it is low then a leak down test will tell where you are loosing compression from, intake, exhaust or rings.
 
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