This motor blows...

#1
My newly rebuilt 283 Chevy creates so much crankcase pressure that it blasts oil out of both breathers and no small amount. It is for this reason that I have not made more than one pass down the track each week. At first I thought i just didnt have adequate ventilation with only the breather on the intake and a pcv in the back. I added the road tube setup but with a clear 1" flexible hose so I could see if oil went through it much. none. Then, I went to the track and at high RPM my motor lost 2 1/2 quarts of oil in one pass. The 283 feels weak and not like my previous 12 second motors. That may be tuning and carburation, but I cant test this when it pushes that much oil out in a single pass. Does this sound like bad rings o anyone? I am wondering if the rings didnt seat. Kind of reminds me of how a super soaker works. any suggestions?

Henry.
 
#4
pressure check?

By pressure check do you mean a compression test, or a cool new different test I can do? I will do a compression test in the morning. Thanks I appreciate the suggestions.

Henry
 

dq409

Well Known Member
Supporting Member 3
#6
55Chevy283 said:
By pressure check do you mean a compression test, or a cool new different test I can do? I will do a compression test in the morning. Thanks I appreciate the suggestions.

Henry
I believe it`s a leak down test.
Somewaht like a commpresion test but you add air to the cylinder and hold it at a PSI and see how much leaks.

You can listen through the exhaust, intake and crankcase to see where the air is going to tell what parts are worn.

Exhaust-intake= bad valves
Crankcase= bad rings

Make sure you are at TDC when doing the test
 
#7
Compression test results

:bang I did a compression test this afternoon. Most cylanders are around 120 psi. One is at 100 psi. another at 105 and one at 115. These are the lowest test values I have seen on any small block I have owned. They must be all bad. The rings are stock iron rings for .080 overbore. The motor was measured 10:1 compression. I think they should have been in the 165 psi range. With the lack of availability of good moly ring sets for this size overbore, I think I will just build another 283 with a different block. I will probably then bore this one out to 4" so I can get good domed pistons and good high rpm rings. What do you guys think about these compression values?

Henry:bang
 

Ronnie Russell

Well Known Member
Supporting Member 2
#8
Henry, two qts in one pass means major problem . Low compression, too low. I would guess rings installed incorrectly. Did you check end gap clearances? Maybe mis-boxed rings? Just a guess.
 

dq409

Well Known Member
Supporting Member 3
#9
Did you give the engine time to seat the rings before you hit the track?

I believe those cast rings take longer then the moly`s to seat !!!

Could be wrong,,, but it would be the first !!!:eek: :roll
 

MRHP

 
Supporting Member 1
#10
rings

I always thought the cast rings took a seat faster but had a tendancy to wear faster and not take the heat as well as a moly ring. Good for stock and mild performance builds. Not a drag race ring.
 
#11
I did check the gaps and gave the engine 500 miles to seat before revving past 3500 and 700 miles before going to the track. The one thing I wish I would have checked is the cylinder walls carefully for out of round condition with micrometers. I just trusted the machine shop and did not check this. Mistake. I am not saying it is the cause, but it is one more possibility that I cant rule out until I tear it down. I am sure I installed the rings with the dots up. More importantly, with the taper towards the top on the top ring and towards the bottom on the bottom one so that they can twist.

I talked to a very helpful guy at Total Seal Rings today who told me he could supply me with some very good rings for that .080 283. He agrees with you guys that that blowby suggests major problems. He said to examine the block very carefully though because there could be another cause like out of round cylinders or rough walls. I will say that this motor shows the weakest compression test values I have ever seen in any of my past 9.0:1 engines with similar cams.

I cant believe the amount of trouble I have had with this motor. It must be cursed.:roll
 
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