|
|
Extreme Veteran
Posts: 363
 
| I've been putting this job off for a while now, sometime back the old dependable 392 dropped a cylinder or two. Today i put it on the rack and gave it a cylinder compression test, the results were as follows
1/ 70psi
2 120
3/140
4/ 105
5/125
6/120
7/130
8/120
Tipped a couple squirts of oil into 1/ and it pumped up minimally to 75-80 psi
So my next thought is to do a cylinder leakage(leak down) test to see where the leak is but my intial thoughts are probably valve/valve seats? If it is valves I'm wondering about the success I'll have with freshened cylinder heads on the untouched cylinders/pistons/rings.
This 300C motor (solid cam) appears to have never been apart (car has 118k miles on speedo which seems to tie with the general condition of the car) and it has never been a "rattly" motor so I'd like to advance diagnose correctly and fix this issue the least invasive way possible rather than just tear the motor completely to bits and have another car off the road for umpteen months.
Any tips /advice, dos and don'ts or what you guys would look for, and how you'd approach it would be very helpful.
Thanks
Owen
|
|
| |
|
Veteran
Posts: 241
Location: Southern CA | Had a similar problem before on a hydraulic lifter engine, not on a Hemi but same principle applies. Used an adapter to pressurize the cylinder with compressed air, after confirming that both valves were closed, since yours is no. 1 cylinder it will be even easier to confirm. I could hear/feel air coming out of the exhaust pipe. Valve springs were fine so I had a burnt exhaust valve and/or bad seat. Valve job fixed the problem. If I was you I would proceed with the leakage test and go from there. Assuming it is a valve, I don’t see why you couldn’t have a valve job done to correct it without affecting the rest of the engine. In my Hemi I always put a lead substitute additive in the gas tank when I fill it, it helps prevent burnt valves. |
|
| |
|
Expert 5K+
Posts: 9650
  
Location: So. Cal | Once you have the heads off, check the cylinders for uneven wear too. But the leakdown test should tell you what is going on. Looks like you have multiple cylinder issues so it is most likely a problem with the valves. Before you do the leakdown though, are you sure the valves are adjusted properly? Poor adjustment can cause these symptoms too.
Edited by Powerflite 2018-01-06 9:40 AM
|
|
| |
Got the 6 1/2 cylinder 392 hemi
