I've just rebuilt a 350 chevrolet engine. I've changed basically everything in the block. Crank, cam, rods, pistons, rings, lifters, pushrods, etc, etc. The engine runs good and strong but when ever it is put under heavy acceleration, oil blows out of the dipstick tube. I wasn't worried about this too much until the engine oil got on the exhaust headers and caught fire! I got the fire out and the engine cranked right back up but now the TH350 transmission will not pull in drive. It still works perfectally in reverse! I checked the modulator hose and it hasn't been burned and holds plenty of pressure. Someone please tell me what's wrong before I've had enough and really blow the thing up! Justin
what rings did you use? and how was the block honed? sounds like the rings havent seated. as far as the trans...mine just did the same thing. I backed the coupe out of the shop. went to put it back in, and no forward gears, works fine in reverse....cant figure it out.
I used moly rings and honed the block until a good crosshatch pattern showed. The trans worked fine before I pulled my "stunt" and released my aggratation.
I suggest you do a leakdown test on the engine. I think you'll find the cylinder pressure is leaking past the rings. Run each cylinder up to top dead center and apply about 100 psi thru the spark plug hole. Listen at the carb, exhaust pipe and the vent on the valve cover. That will tell you where the leak is. I bet you hear leaking at the valve cover vent. Rings. Ron
without knowing how the crankcase ventilation system is set up, it's hard to say why it's blowing out the dipstick. Does it have a pcv valve? does it have a breater on the other side of the engine? if there are no vents, then the pressure will find the path of least resistance. If the vent system is ok, then it has a serious ring or guide problem. Most TH350 failures are with the forward clutch, which wipes out forward motion but reverse still works. Hopefully it's something easier to fix, but be prepared for another rebuild.
Squirrel: I have a pcv valve and an oil breather cap on the covers. The pcv valve is working correctly also. I had the machine shop check the heads and he said they were working right and the valves were not leaking. I'm at a dead end scratching my head
Did you carefully look over the vent in the valve cover, some valve covers come with a plug that looks like a grommet, and some breathers have a very small opening in them, not punched out all the way. Does the engine put out any blue smoke out the tailpipe?
the engine doesn't have blue smoke out of the tail pipe and the breather is punched all of the way out.
The only thing that will cause oil to be pushed out of the dipstick is excessive crankcase pressure. Normally this is caused by holes in pistons, broken rings etc. A PCV problem could cause this but not normally
It's blow-by, pure and simple. Now where is the blow-by coming from? Tha'ts the question. I'll bet a cracked piston or boken rings or the compression rings were installed upside down allowing compression to slip by the rings. Good luck.
`Did you think that maybe a cooler line leak is your real problem.I have seen many burnt out 350s from being run low on oil.
I figured out the transmission today. I burnt the forward clutches. That's why it was going in reverse but not forward. I hope your suggestions will help me figure out the other problem. Justin
Sometimes the hardest things to figure out are actually butt simple....cant just be -it is overfilled with oil, is it? I have done it ......... it can easily slip by you- or ESPECIALLY== if there are 1 too many "cooks in the kitchen" I'sd say if a piston was broke or rings broke it would run poorly due to loss of compression.....if not the above check and re check the venting and especially the vacuum source to the PCV......
I had the same problem with an engine and after running a LEAK DOWN TEST, I discovered that it was leaking from one cylinder to another due to a bad valve job. So like the other guys said run a LEAK DOWN TEST.
O.K. you said you installed new pistons was the block bored. I've seen ring grooves cut out and bust new rings because the groove can't be cut completely out. Broken compressions rings would cause blow by but not oil consumption because the oil rings are further down the bore. If the block was bored were the piston clearances checked?
I blow oil out my breather tube a bit I figure it's compression rings but I've cleaned out the oil passages in the head and it's lessened a lot.
Run your PCV hose from the valve cover to the intake manifold under the carb if you haven't. Fixed the exact same issue after we rebuilt the motor. It's the simplest thing to try first.
was the proper grit used in the honing process, was it followed with a plateau brush? moly rings take a very specific honing process, and a very specific RA. the rings are lapped in from the manufacture, and want a cylinder bore that resembles an engine that has already been broken in......this is why when you first fire a moly ring engine , the rings are virtually seated upon firing. put a rough finish to the bore , and sometimes they will never seat
I had the same issues with my .060 over 350. Tore it down and found the secondary rings were sticking in the land and therefore not sealing properly.
I have found that most of the cheaper rebuilder style moly rings will still seal on the old school rough crosshatch pattern meant for cast iron rings. I think its because they are usually just a cast iron ring with a moly spray or insert. The good moly rings want a 600 grit stone with a plateau brush to sweep out the swarf and knock the tops off of the peaks caused by the honing. Definately do a leakdown test to see how much the cylinders are leaking and where. You can also get some info from a compression test. Do one dry and record the result, then squirt a teaspoon of oil into the cylinder and do a wet test. If the reading comes up noticably the rings are not sealing. A fresh engine should have only a few % leakdown and a wet compression test should be similar to a dry one.
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