1941 Compression Test Results-Ugh-(Long post)

[Jim Govoni CLC 20546]

My 41 has 42,000 miles on it. A recent purchase, my fellow 41 owners observed a "skip" at idle. I could only hear it when standing at the rear of the car and could hear a pfffft, pfffft, pfffft, sound as the car idled. On our maiden voyage to Hershey (260 miles RT) she did well. It was 80 degrees the trip up and I met many friends who looked over the car. Suggestions were to replace the belts and hoses as they looked original. Upon replacement they were really bad. After Heshey on a local drive we started up a hill and the car stopped. Restarted fine but then stopped. I had the car flatbeddded back. Lot's of large rust particles in the fuel pump bowl lead to a full fuel system replacement. Tank, added electric back up pump, added fuel filter and a carb rebuild. At that time it was apparent that the wiring was really bad, so I was lucky enough to meet Marty Watkins at Hershey, he has rewired a few 41's so I asked him to do mine. He was such an expert that a few of the guys at YandZ wiring knew him because he made great suggestions. That's where the car is now. With the replacement of all the hoses the cars temp gauges shot up to hot after about 10 mins. of idle. I checked my engine with an infrared temp thermometer. All were 200 degrees or below except the manifolds. This condition continued after the rewiring so Marty and I were stumped. The water pump was pulled for a rebuild and Marty checked the compression, here are the results:PSI compression readings -
Left (driver's) side,                       #1) 105
                                                   #3) 90
                                                   #5) 25 (bad!, that's the one)
                                                   #7) 115

Right (passenger side),               : #2) 115
                                                   #4) 75 (fair)
                                                   #6) 98
                                                   #8) 96
Any thoughts going forward would be appreciated. At a minimum it looks like a full valve job in the near future.  Thanks,  Jim

[savemy67]

Hello Jim,

Generally, when a cylinder is suspect, as your #5 is, repeating the compression test after shooting some motor oil into the cylinder might indicate if the problem is with that cylinder's rings or valves.  If the addition of the oil results in an increase in the compression reading, the rings (or cylinder) may have significant wear.  If the oil results in no change in the reading, valves are implicated.

If Marty can do a leak-down test (by pressurizing the cylinder with compressed air), a more definite diagnosis might be obtained.  A leak-down test can point to which valve (or both) might be the culprit for the low reading.  Or, the test might point to rings/cylinder wear, or a cracked casting if bubbles show up in the coolant.

There are a number of other things that can be involved (mostly with the valve train), but as thorough a diagnosis as possible will hopefully save time and money.

Respectfully submitted,

Christopher Winter

[TJ Hopland]

Yep I would see where the compression is going.    Is this a flathead?   Does this have hydraulic or solid lifters?   If solid maybe just needs a valve adjustment?

[Jim Govoni CLC 20546]

Yes, it's a 346 Flat head V-8

[Paul Phillips]

Jim
Suggest you do a leakdown test on 3-4-5 cylinders, since they are the ones reading lowest.  With the test cylinder at TDC, pressurizing the cylinder with air will indicate the leak down path.  Air bubbles in coolant are head gasket problem, air hissing in intake is intake valve, air hissing in exhaust is exhaust valve, air coming from oil breather are bad rings.

Good hunting!

Paul

[Jim Govoni CLC 20546]

Thanks Paul, that's exactly the plan soon. I'll post the results. Going to Don Miller in the next couple of weeks.