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05-01-2012, 07:24 PM
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Pistons and rings cracked
I just finished rebuilding a sbc 350 which had a problem with extreme blow by coming out of the valve covers...tore engine down to find 4 pistons (#1,5,8,6) had cracked ring lands, rings, and #5 cam side skirt broke off. Engine was .03 over and I had originally put std rings so I gave the damage up to that...Finally get the rebuilt engine with .03 rings and pistons (hypers) and only about 40 miles later the same extreme blow by coming from valve covers....Have not had a chance to do any tests or tear into it to see what is causing it this time but I have a pretty good feeling its either the rings or pistons cracked again....I am completely stumped as to wy this is happening....Any suggestions??????????
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05-01-2012, 07:33 PM
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Wrong pistons/heads, wrong timing, wrong gas, pre-ignition, overheat. one or more of the above..
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05-01-2012, 08:21 PM
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Are rings file to fit? What were your end gaps?
__________________
Horsepower is how fast you hit the wall. Torque is how far you take the wall with you. Midnight Sun Street Rod Association
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05-01-2012, 08:26 PM
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Sounds like to me the rings were too tight and butted together and when they have no where to go they will crack the ring lands. Did it happen again? Idk what did you set the top and second ring gaps to?
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05-01-2012, 09:30 PM
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There are KB hypereutectic pistons that need more top ring gap than 'normal'. If you have a set of those in it and the gaps were set the way a cast piston is usually gapped...
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05-02-2012, 08:53 AM
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Quote:
My friend bought some of the same pistons via the internets; no paperwork. He set up a conventional ring pack and cracked or distorted the ring lands in all 8 pistons. Why only 4 pistons though. You may have several problems manifesting themselves here. Did you check for interference with the valves? Was the block decked? Heads shaved? What is your compression ratio and what fuel are you running. What are you using for timing? you might want to post your assembly procedure for us to look at. Not to judge, sometimes we miss a step.
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05-02-2012, 10:16 AM
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Does anyone know if the KB-231 require this larger ring gap? Thats what I have in my engine and have had ring seal issues with it.... i just wanna rule this out.
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05-02-2012, 11:16 AM
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Quote:
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05-02-2012, 02:35 PM
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Quote:
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05-04-2012, 07:16 PM
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Sorry havnt got a chance to get on here lately....new in the engine building area and did not know about having to check the ring gap ooops....thinking back they did want to go in pretty hard so im thinking the rings needed to be filed to fit just right and ended up cracking on the way in.....hoping to have it tore down next week sometime and i'll let you all know what i find
Thanks for the responses they really helped!!
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