help on overhaul failure

Thanks for post: Yes, I did mean .003 instead of .030. I think the pistons that failed were the new design short skirt pistons but were made in China. I will check further on how measured.
 
James Rogers, I read your post on Siamese cylinders and you mentioned DRILL THE HOLES. Are you referring to the water hole in the 5.5 head that is not drilled out?
Thanks,
 
Here is a picture of the scored pistons removed from my engine. At the time the pistons scored, the water temperature was at 180 degrees as measured from a sensor in the upper hose. It is possible the water could have been low enough in the block to score and melt the pistons and still be at 180 degrees?
Thanks,




IMG_4298.jpg
 
sounds to me like it got really hot in that one area. the one time i scored a cyl was when i was 16 it was on a snowblower I was over revving it on the benchtop like a jack *** got it hot stalled it then pulled the start rope and the piston dug in . I would blame heat.
 
Plainsman30 said:
I did talk to the builder. The piston clearance was .030 on all 4 cylinders when it was assembled the first time. Cylinders have now all been honed again, so clearance will be a little greater than .030. The builder will measure all 4 cylinders before final assembly to check clearance. The builder said rod bearings didn't show too much stress, but he polished the journals and will put in all new bearing inserts.
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Wrong Ring gap
 
Wow, that is a new one. I agree that the .003 clearance mentioned in previous posts is not the issue here. Typically the clearance is measured 90° from the pin CL and below on the skirts. The area shown between the rings is typically clearanced more than the skirts and should never contact the bores.

That said, I would look at two things;
How straight are the rods, I have seen new rods that should never have been released.
Are the back two bores square with the crank? I know there is an offset to the thrust side (offset .125) If you lay a straight edge down the main bores and use square are the front and rear sides of the bores square to the crank?
Heck, even check to make sure the mains are level to the block (front to rear).
In any event, you may wish to try other pistons.

John
 
Plainsman30 said:
Here is a picture of the scored pistons removed from my engine. At the time the pistons scored, the water temperature was at 180 degrees as measured from a sensor in the upper hose. It is possible the water could have been low enough in the block to score and melt the pistons and still be at 180 degrees?
Thanks,




View attachment 250997
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Where did the pistons come from?

Tom Endy
 
Is it possible that when the head gasket blew and coolant washed the oil away locally and caused local overheating, scoring and welding? Or could the head gasket have been failing for a time washing the oil away so the pistons were running dry longer than realized?
Al
 
Guesses are abound but the only way to really find out is to perform a proper diagnosis to find the cause of failure.
 
haha true you need to find someone with a dial bore indicator who knows how to use it.
Bores could be out-of-round, tapered, etc. Other measuring devices will not give enough info. Then you need to pick the right clearance number
 
I'm talking from cooling system, lubrication system to mechanical specs, or operator error....an experienced person is needed
 
"When the pistons scored, it was loud and sounded like a semi truck applied the engine brakes right beside me. There was a lot of smoke, but the engine didn't seize up and I did get home with it."


You said you were able to drive the car home after the head gasket blew.(By the way, that loud smoking condition sounding like a semi truck jake brake,was not the piston scoring, it was the head gasket blowing out) Driving the car after blowing the gasket with perhaps s lack of water and/or a "milkshake lubrication" caused the scoring while driving the vehicle home, however far that was.
 
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I would agree with "mikeinnj" that the blown head gasket and the resulting drive home coupled with the missing vent hole in the head caused your over heating and the piston scoring. I would put everything back to way it was, checking and double checking piston and ring gap clearances. You said in the beginning that you are running a 5.5 CR head. When running with that head your advance should be at least 10 degrees less than you were running with a stock head. You also stated in your first post that you were running with the spark advance 1/2 way down (that's about 20 degrees if the timing was set to TDC). Depending on the driving conditions at the time of failure, it could be too much advance and caused the head gasket to fail.
 
Plainsman30 said:
When started the rebuild last spring, the found the old block was cracked, so we had to find a different block. Rebuild included magnifluxing, cooking, and decking the block. Cylinders were rebored 80 over, new pistons, counter balanced crankshaft, inserted rods and mains, new stainless valves, and 5.5 head. The pistons were a modern type with Teflon coating and thin rings. The carb, distributor, cooling system, exhaust system, and drive train are stock and unchanged since motor was overhauled.

At 530 miles the head gasket blew and coolant filled the back 2 cylinders. At 1100 miles the back 2 pistons scored. When they scored, I was driving 45 against wind, GAV open about ½ turn, advance lever down about half, water temperature at 180 and I was running about a 50/50 mixture of 10-30 and 10-40 oil.

The scored areas “face” each other. In other words, they are on opposite sides of the cylinder wall and are in the same area where the head gasket failed.

In trying to figure out what happened, machine shop checked the cylinder bores and rods, which checked out OK. We checked all the water passages in the block and the head.Everything was clear, except one hole in the 5.5 head was not open.We checked a stock head and the hole is open. We contacted the supplier of the 5.5 head, who said the hole were dead end and does not serve as a water passages.

I am not trying to blame anyone, but would like the engine to hold together next time.So far, we plan to put it back together using a stock head and stock type pistons. It was also suggested to run the GAV open further.

Any other ideas would be appreciated.
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Did the head gasket blow before the pistons made noise, or after the engine got tight?
I'd guess the gasket went between the two cylinders first, then the coolant washed the oil away from the scored area on the pistons, otherwise, it would seen the thrust side of the piston would be the first place to score.
I'd like to see the rod bearings from those two pistons.
Lots of good suggestions have been mentioned, and it seems all bases have been covered.

When you get the engine redone, be sure to do a lot of heat/cool cycles, and recheck the head nut torque several times. Also drive very easy for the first 1000 miles to break in the engine. :)
 
"I'd like to see the rod bearings from those two pistons"

Tom, I'd like to see all the bearings

Plus we have no way of knowing the QC on that piston....truly round, truly cam ground, cam ground the wrong way, etc etc. What spec is allegedly being followed?

QC is not what it used to be. I am seeing re-pop forged rods that I have to resize because the big ends are NOT round. I am seeing new shells that vary in width by .010 or more and are binding on the crank filet. Unless you measure and remeasure every possible dimension of re-pop parts these days you do not know what you have in your hand. And you need the correct precision tools to make this happen.

Head gaskets have been blowing for many many years and not necessarily taking out pistons at the same time; else every blown gasket would have required a total teardown

A very thorough failure analysis of this motor is required
 
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Here is some more information to try and answer the questions that were posted:
1. It is hard to see the coolant level because of the baffle in the radiator neck. So it is possible the water level may have been down a little at the time the pistons scored.
2. The head gasket blew at 500 miles.We put it back together, and the pistons scored at 1000 miles.The head gasket looked very good at 1000 miles when disassembled.
3. The new pistons and new inserted rods probably came from Antique Engine Building. The rods were stamped “USA” and the pistons were made in China.
4. I don’t have the bearing inserts. I was told they showed a little stress but were not bad.
5. A reputable machine shop checked the rods to be sure were straight and also did lots of tests on the block and couldn’t find anything wrong. Water passages in the block seemed open.

Thanks,
 
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