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Post by baconsarnie on May 13, 2017 15:02:02 GMT
Had a puff of burnt oil on overrun for a long time now, it never really got any worse and had become a bit of character for the car(!).
However, that puff has rapidly turned into a battleship style smoke screen on high rpm overrun during the last couple of race days. Initially I assumed valve stem seals, but they were replaced fairly recently when I refreshed the head...
I've done a compression test to try and get a root cause, results are:
Cyl First Pulse Final Pressure Wet Pressure 1 65 138 200 2 80 145 195 3 80 145 192 4 80 145 195
(all PSI, warm motor)
Do you agree that those results indicate the piston rings are pretty badly worn throughout?
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Post by wannabe on May 13, 2017 15:52:41 GMT
Would a Leakdown test help diagnose the problem? I'm not quite sure what it does/will tell you, but I'm aware it complements the compression test lol
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Post by baconsarnie on May 15, 2017 9:45:56 GMT
Leak down would help identify poor valve stem seals... but i 'think' that's not the problem here... I think the wet test results rocketing up shows naff rings... was hoping for someone to back that theory up tho!
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pewe
Chats A Bit
Posts: 157
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Post by pewe on May 15, 2017 10:04:32 GMT
For what it's worth on my 1.6 Na it recently showed c.200 on final pressure. It does puff either oil smoke or rich mixture (s/c doesn't currently have an i/c so runs rich) on start-up after standing. If not over rich mixture I've put that down to stem oil seals but will live with that. Trailing smoke after high speed run on the over-run sounds like rings to me. Depending on which Mk I believe Mk2's can have probs with oil control rings but Horney's the guy to ask about that!! HTH. Cheers, Pewe.
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Post by martiny on May 16, 2017 10:04:26 GMT
... I think the wet test results rocketing up shows naff rings... was hoping for someone to back that theory up tho! I think you're right. That's a big jump from dry to wet, which implicates the rings. The dry results are still within Mazda's spec, which is something like 125 or 135 psi, but it's still pretty low.
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Post by baconsarnie on May 16, 2017 11:19:32 GMT
Ok, that's giving me some confidence in my diagnosis... looks like a winter rebuild for certain! Cheers!
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