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| Compression OK, Leakdown NOT OK http://ducatittandf1.com/viewtopic.php?f=24&t=12049 |
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| Author: | TheClaw [ Sat Nov 28, 2020 9:03 pm ] |
| Post subject: | Compression OK, Leakdown NOT OK |
Just some off season fun. I wanted to run some diagnostics before I start my winter "up-fixen". I ran a compression test and both cylinders are 135psi +/- 4 so I'm ok there. However, after painstakingly finding TDC i run my leak down and it not only leaks but sounds like the exhaust valve is slightly open. Some of you might remember, this is a Reno bike. I have what looks like an early A motor with Montjuich cams. Reno stroked it a bit. You can see the gap between the case and cylinder and the studs don't go all the way through. About two years ago Palmer helped me (basically I watched) time the cams to the Montjuich specs. So I have some overlap, right? The bike runs, it's not a rocket, but respectable. Thoughts? Comments? Thanks, Jeff |
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| Author: | 618F1 [ Sun Nov 29, 2020 1:46 am ] |
| Post subject: | Re: Compression OK, Leakdown NOT OK |
Maybe reading page 6 of my postings of the 1980 factory Pantah racer replica, in the Bike Build of the Year section, will help some. Maybe there are degrees of a part failure. From that experience, and some recent valve work I’ve done on some heads, I have learned that the sound cannot be ignored. But, as another thought, it would not hurt to check both shim measurements on that valve first. MikeV Q: What lobe center did Palmer use? Do you remember? |
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| Author: | TheClaw [ Sun Nov 29, 2020 9:18 am ] |
| Post subject: | Re: Compression OK, Leakdown NOT OK |
Not sure but at the time we adjusted the valves while we were in there. |
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| Author: | TheClaw [ Sun Nov 29, 2020 7:59 pm ] |
| Post subject: | Re: Compression OK, Leakdown NOT OK |
I fiddled with this some more today. I hooked up the compressor to the cylinder and just lightly cracked the air open. I could easily hear the hiss of air come through the carb as the intake valve opened, slow, stop, then come out of the exhaust, as I turned the motor over. I had it it gear so after experimenting with it a bunch of times, I decided to try again. When the hissing stopped I locked it up with the brake and dialed up the pressure. It didn't take much before the air started rushing out of the EXHAUST valve. If the cylinder was pressurized I would think it would keep the valves closed unless the exhaust valve is open just enough to move when I turn up the pressure. Maybe the valves and seats are worn enough to let a lot of air through even at TDC. I'm stumped. Jeff |
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