Technical > Matt Shaff's Engine Shop

Cause of fretting on main caps?

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Dunc the Funk:
We only put 13 passes on our blown methanol BBC last season. I was surprised to find serious fretting had occurred on caps 2,3 & 4. 4 was loose in it's register.
As far as I know this did not happen last season when we probably did 20 odd passes. Is there anything I should think about with the tune that may have caused this?

jeff/21:
cap walk,caused by weak caps and/or studs

dreracecar:
Just the studs or are there "ring dowels" around the studs to locate the caps?

dusterdave173:
Tune up
When timing too high etc or tune up is off there can be detonation--pre ignition etc
That is your culprit--back timing off some  Find out where the tune up issue is
I worked in engine shop for decades--even cross bolted hemis's etc will do it if timing too advanced etc
With correct tune up that goes to a minimum
Engines can run great ET's etc but are killing themselves half way down the track and you can't hear it
Plugs and main caps tell the tale

Dunc the Funk:
Tune has been all over the place as we started the season with a failing fuel pump. This got it down to the leanest it's ever been where the plating was off the plugs down to the first thread. Still, it ran 184mph on an 8.4 with an on/off/on/off launch. Then we got a new pump & it went crazy rich even though I changed the pill because I expected it to be rich.

Not had more than 34 degrees advance in it so far.

We have just had the block & caps machined, doweled & line bored by a very experienced machinist. Getting it back on Tuesday.

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