DLK Posted October 3, 2011 Report Share Posted October 3, 2011 Reading some recent posts by Barabbas, Greg_g and some others it looks like readings under 100 are a good sign the rings and possibly valves in my engine are showing serious wear. I finally tested my compression and got 90/95/100/110/95/90. So no really dead cylinders but some pretty weak ones. For the most part it runs smoothly and has decent oil pressure, although after driving 50 miles Saturday the idle pressure was down around 15-20 which doesn't seem that bad. If it weren't for the increasing smoke clouds at stoplights and on deceleration I would live with this but I guess I better prepare the wife for a hefty 2012 investment in the Wayfarer. As Rockwood said in an old 2008 post I too was surprised to see the plugs after two years looked fine - the light brown color and not fouled at all. I would have thought that with bad rings and an engine burning a lot of oil it would show up on the plugs. Quote Link to comment Share on other sites More sharing options...
aero3113 Posted October 4, 2011 Report Share Posted October 4, 2011 I wouldn't call 90 PSI a "pretty weak one" that's not bad at all. All you might need is a good valve adjustment. Also your oil pressure seems ok also, any pressure above 0 at idle is acceptable. Save the $ for a nice gift for your wife(I think I just scored some points with her ) Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted October 4, 2011 Report Share Posted October 4, 2011 How often must you add oil to your engine? Quote Link to comment Share on other sites More sharing options...
greg g Posted October 4, 2011 Report Share Posted October 4, 2011 was your compression test done cold and dry or warm and wet? Quote Link to comment Share on other sites More sharing options...
Rusty O'Toole Posted October 4, 2011 Report Share Posted October 4, 2011 When you do a compression test you can check the worn cylinders by squirting in some oil and retesting. If compression comes up the problem is rings, if it does not the problem is a burned valve. It sounds like you need an overhaul not a complete rebuild. Grind valves, hone cylinders, replace rings, possibly new bearings. Such a job can be done at home without removing the engine from the car, except for grinding the valve seats. Cost around $500. Quote Link to comment Share on other sites More sharing options...
DLK Posted October 4, 2011 Author Report Share Posted October 4, 2011 How often must you add oil to your engine? I have only put 300 miles on the car this year and have gone through 2 1/2 quarts. Now some of that is coming out the rear seal - I have a nice puddle on the garage floor after very drive. Quote Link to comment Share on other sites More sharing options...
DLK Posted October 4, 2011 Author Report Share Posted October 4, 2011 was your compression test done cold and dry or warm and wet? I drove the car long enough to get it up to operating temp before taking the readings. I am surprised to hear that my compression readings aren't that bad. In some other posts I have seen readings of 125-145 lbs. Quote Link to comment Share on other sites More sharing options...
DLK Posted October 4, 2011 Author Report Share Posted October 4, 2011 I wouldn't call 90 PSI a "pretty weak one" that's not bad at all. All you might need is a good valve adjustment. Also your oil pressure seems ok also, any pressure above 0 at idle is acceptable. Save the $ for a nice gift for your wife(I think I just scored some points with her ) It's a good thing my wife does not access this forum. At the least I would like to reduce the smoking and the size of the leakage. Everytime I visit a friend I have to park on the street because of the large amount of oil that drops out the rear of the engine. I think my 50 has the neoprene rear seal rather than the rope seal so apparently it can't be fixed without dropping the crank. Quote Link to comment Share on other sites More sharing options...
DLK Posted October 4, 2011 Author Report Share Posted October 4, 2011 When you do a compression test you can check the worn cylinders by squirting in some oil and retesting. If compression comes up the problem is rings' date=' if it does not the problem is a burned valve.It sounds like you need an overhaul not a complete rebuild. Grind valves, hone cylinders, replace rings, possibly new bearings. Such a job can be done at home without removing the engine from the car, except for grinding the valve seats. Cost around $500.[/quote'] So can a neoprene rear seal be fixed without removing the engine? I assume if the crank needs to be sleeved it would have to be pulled out of the car. As bad as my leak is any work would almost have to include that repair. I realize these flatheads almost all have some leakage but mine is really bad. Quote Link to comment Share on other sites More sharing options...
busycoupe Posted October 4, 2011 Report Share Posted October 4, 2011 My car also has the neoprene rear main seal and was leaking quite badly. Last summer I dropped the oil pan and removed the rear main bearing cap. The bottom half of the seal bolts to the bearing cap and the top half to the block. I replaced the bottom half of the seal, but could not remove the top half without removing the transmission and fluid drive unit. I left the top half in place, but checked the tightness of the bolts holding it. I replaced the oil pan gasket and out it all back together. This solved better than 90% of the leaks. I still get a dime sized spot on the floor after a ride, but a drip pan easily takes care of that. As for your compression numbers, 90 to 100 lbs may be close to normal if you have a low compression engine. Normal atmospheric pressure is 14.7 psi. If you have a 6.5:1 compression ratio 6.5 x 14.7 = 95.5 psi. Any engine is going to leak a little pressure, so 90 psi is OK. I would be more concerned about the cylinders all reading close to the same rather than all being over 100 psi. Dave Quote Link to comment Share on other sites More sharing options...
cole18cars Posted October 4, 2011 Report Share Posted October 4, 2011 Also remember that the psi goes down as the altitude goes up. Quote Link to comment Share on other sites More sharing options...
Rusty O'Toole Posted October 5, 2011 Report Share Posted October 5, 2011 (edited) I drove the car long enough to get it up to operating temp before taking the readings. I am surprised to hear that my compression readings aren't that bad. In some other posts I have seen readings of 125-145 lbs. OHV engines typically have higher compression than flatheads. Your flathead in perfect condition might go 110. Anything over 100 is considered very good. ................................................................ Later I have been trying to find what is normal compression pressure for flathead Chrysler engines. It turns out it is hard to pin down.Have not been able to find any official recommendation in any manual. As near as I can figure, 110 would be perfect for a prewar engine, 120 for a post war engine, the last ones with higher compression 130. Edited October 5, 2011 by Rusty O'Toole Quote Link to comment Share on other sites More sharing options...
DLK Posted October 5, 2011 Author Report Share Posted October 5, 2011 My car also has the neoprene rear main seal and was leaking quite badly. Last summer I dropped the oil pan and removed the rear main bearing cap. The bottom half of the seal bolts to the bearing cap and the top half to the block. I replaced the bottom half of the seal, but could not remove the top half without removing the transmission and fluid drive unit. I left the top half in place, but checked the tightness of the bolts holding it. I replaced the oil pan gasket and out it all back together. This solved better than 90% of the leaks. I still get a dime sized spot on the floor after a ride, but a drip pan easily takes care of that. Dave What you say is encouraging. I have owned a lot of Mopars over the years and those from the 70's and 80's all leaked oil so I am not looking for perfection just avoiding the pool of oil I leave now. It sounds like a new bottom half of the seal and new oil pan gasket would significantly reduce my problem. Quote Link to comment Share on other sites More sharing options...
JohnTeee Posted October 8, 2011 Report Share Posted October 8, 2011 Since I just ran across these: 1947 P15 Special Deluxe June '77 127K Miles - 90/85/90/100/80/90 November 142K Miles- '02 95/85/90/90/100/90 No engine work in between. Have some minor oil leakage from the rear of the engine after driving. Cheers! John Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.