rodgling
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| posted on 23/4/12 at 10:44 AM |
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Is my crank ruined?
Following on from the knocking noise, I took the sump off and found that I'd spun a big-end bearing. No loss of oil pressure. The bearing is
heavily worn but still present. There are some small marks on the crank though that I can only just feel with a finger:
I hope that these are just deposits of bearing material and that I can clean these off without removing the crank.
What's the best way to go from here?
Current plan is to measure the crank with a micrometer, and if it's thicker where the marks are, use a copper scraper or some wet & dry
maybe to remove them? Then new bearings and put it all back together?
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steve m
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| posted on 23/4/12 at 11:00 AM |
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I would be inclined to take the crank out and check all of them first, and possibly get it reground ?
steve
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RAYLEE29
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| posted on 23/4/12 at 11:02 AM |
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Hi, it looks to me from your pic that you should be able to clean that up ok what does the con rod look like? carefully use some emerycloth/wetndry
wrapped over something like a file then check size with a mic. the question then will be why it happened in the first place.
Ray
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RAYLEE29
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| posted on 23/4/12 at 11:07 AM |
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also agree with above on checking for other damage but do think that your crank would go again without a grind as long as its in spec and you can
remove all trace of the deposits on it.
Ray
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rodgling
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| posted on 23/4/12 at 11:13 AM |
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quote:
Originally posted by steve m
I would be inclined to take the crank out and check all of them first, and possibly get it reground ?
Yeah, crank regrind is the "best" option. It is a lot more time / effort / money once the crank has to come out though, so if it looks as
if I can repair this without going down that route I would prefer not to.
Obviously I'll at least check all the big-end and main journals and replace all the big-end bearings.
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Daddylonglegs
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| posted on 23/4/12 at 11:41 AM |
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I agree with above. Check all journals first then if OK and within tolerance I would use some scouring pad lightly to remove the deposits (with a
little meths or similar) then use 1200-1500 crocus paper. I've used that stuff to polish up lightly scored bike front shock tubes and never had
any issues afterwards.
HTH
It looks like the Midget is winning at the moment......
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mark chandler
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| posted on 23/4/12 at 11:45 AM |
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Its not scored all the way around, just looks like a few deposits, if it was me I would clean with fine emery and reshell, petrols are move forgiving
than diesel engines.
At worst you waste money on shells, if it carries on without any further issue then £100's saved in the bank 
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paulf
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| posted on 23/4/12 at 01:17 PM |
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If the bearings have spun in the rod then you will need a new rod, there is only half a thou tolerance in the rod bore and it will most likely be oval
if you drove it far .It is sometimes possible to reclaim rods by machining the cap and rod faces and re boring and honing if not to bad.If the shell
did not actually spin then you may get away with just new bearings but I would want to take the crank out and make sure the oil ways were clear as the
obvious reason for the failure is oil starvation to that big end, also the old bearing material will now be spread throughout the engine so if
intending to keep the car I would strip the engine and make sure its all clean before rebuilding it.
Paul
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Chippy
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| posted on 23/4/12 at 01:18 PM |
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I have just overhauled my sons VW bus engine, which had siezed solid, due to no oil pressure because the, (very well known), engine rebuilders had
left out a blanking plug. All of the bearings had gone, (as you would expect), but we cleaned up the journals with a thin strip of 1200 wet and dry
with some thin oil as lube. The conrods were then trial fitted using Plastigauge, and were all found to be well within limits, (1.5 thou). So if you
clean them up and then trial fit the new shells using the Plastigauge method, and find them within 1.5 to 2.5 thou just rebuild the engine, making
sure that the shells are correctly fitted. HTH Ray
Edit to add, as paulf has said you will of course need to strip the engine, (should have said that in my piece).
[Edited on 23-4-12 by Chippy]
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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Paul Turner
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| posted on 23/4/12 at 03:38 PM |
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Rebuilding it without cleaning all the engine thoroughly will be a big risk, any bits left in the oil ways will quickly kill the engine. This will
100% be certain to happen when you clean the crank.
IMHO since a polish at a machine shops costs very little and spoken to nicely they will clean your engine bits in their machines it would be daft to
try and bodge it.
Do it once and do it right.
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jollygreengiant
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| posted on 23/4/12 at 04:11 PM |
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quote:
Originally posted by rodgling
I can only just feel with a finger:
I think you will find that this is the 'most' pertinent part of your post.
First metal does not 'stick ' to metal for no reason, over heating HAS occured. So ALL journals will need checking and the oil ways and
pump, question WHY has it got that hot?
Secondly IF you can 'FEEL it', then, in terms of crankshaft bearing faces, its either too high or too low, in this case, too high.
I would suggest 1000 (or higher) grit emmery tape, oiled as used, just to clean up the faces and then check all crank journals for tollerance and
ovality. Then decide what to do, however, I suspect that a regrind will probably be the order of the day with new bearings probably a block clean and
re-ring might well be the order of the day.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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owelly
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| posted on 23/4/12 at 05:24 PM |
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IMHO, the engine needs to be stripped. I wouldn't recommend using any sort of emery paper to clean the journals other than some crocus paper and
oil to highlight any potential high spots on the journal. As said, there is a reason why the bearing failed so you need to find this. Plus, the rest
of the engine may have survived this time but running it without a proper strip and clean could well render the rest of the engine scrap. Bite the
bullet and do it right.
http://www.ppcmag.co.uk
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