Asbo's pop goes blown small block

Attachment 66500


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Compression is good and Within 10psi on all cylinders .. the rust is at bottom of the bore

The additional info about compression makes aside a difference, I think. Ordinarily any such markings in the walls would require boring, or just a honing if you get lucky. You've not mentioned whether they pass the fingernail catch test or not. Irrespective, you have decent compression which suggests, and it looks like it too as far as I can see, the damage isn't where the rings pass, but below it, just! Also, it looks like the damage is perpendicular to the crank centerline which in my mind means its not in the thrust area caused by the rod angularity, so unlikely to be an issue? How is the piston looking in that area?

Is the piston to wall clearance ( generally, not just the damaged area) in spec? Thinking about piston slap.

Are the pistons / rods assembled and installed correctly, thinking particularly of the fore / after orientation. I'm guessing that could cause a knock somehow if done wrongly, otherwise there wouldn't be orientation requirements.

Why would you suspect the wrist pins? And what about valve to piston clearance, piston to deck height and other sources of potential interference?

How bad / noticeable / embarrassing is the knock if you were to live with it?

Bummer nonetheless.

Chris

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Thanks for the reply chris..

as you say the damage is below where the rings pass - but the skirt of the piston does go down this far... ... the rust protrudes into the bore - can feel with fingernail .. unsure how to describe - feels a high spot rather than eaten into the bore if makes sense?

it sounded like it was comin from small end sort of area was my initial thinking - thats why suspected wrist pin .. but all that looks ok now but as said its all obviously cold now .. piston to bore appears fine in all other bores - I may put that one back in later and turn by hand and see what happens when the piston gets to the damaged area... my thinkin is it could be knocking?? no obvious damage to piston..

its too bad/emabarrasing to put back as it was put it that way

I was just going too say any piston damage. Check the cam and followers. Examined the plugs ? Are you sure the timing was right for a blower motor and not getting knock ? Don't get side tracked by that bit of rust on your gault finding !

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was definetly worse once it got warm - cam and lifters all fine - plugs fine -

timing was safe - and only had knock in one place -

nightmare trying to find what it was ..

Gutted to see this mate!
obviously hard to give an opinion when you haven’t heard the noise, would have said above about the rust being too far down to hurt comp, but is it expanding when hot and catching the skirt? Any markings ?
What to the bearings look like?
how close are the rods to the block at there out most swing near the sump rail.
Lifter bored ok?
rocker to cover clearance ok?

my thinkin was same once i saw the rust - is the skirt expanding when hot and catchin it? no obvious marks on piston tho - ill get pics later or mora.. could it move piton enough to slap it about? I dint see the rust until took that rod out - may put it back in and turn by hand see what happens to the skirt when it gets that far down..

bearings on that rod look fine - not looked at rest yet

rod to sump rail ok

lifter bores fine lifters spin lovely

rocker to cover cleareance plenty - nice covers i had from you ;-0

gutted indeed - thought this part of the build was all wrapped up

thanks again for your thoughts lads

I'd lightly sand the rust off (making sure to REALLY mask up area first!).
Piston slap only occurs when cold and goes when hot.

Are you sure the cam is ok?

Not something on the crank catching on the block due too lack of clearence. Slightly longer bolt on one of the rods. Any rub marks anywhere.

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yea i get that occurs when cold but could the opposite happen here where by once is hot it knocks that area? grasping at straws.

lifters all looked perfect - will try get a better look at cam later -

anyone want a cheap small block? haha

and to john - ill double check everything either later or tomorrow see what time i get - but nothing obvious but was late by time finished up last night..

Get a dial gauge on each cam lobe to check the lift on each one - at least it will rule that in or out then.

As John says, pull the sump and check for conrods hitting the block skirt - is it a stroker crank? if so the block skirts do need clearancing if it is. Rods will grow as they get hot so it may be that.

Sorry - piston slap goes when hot.

yea not a bad idea to put dial indicator on cam - i'll def do that

sumps off - stock stroke crank and rods

With the rust being high I'd deffo knock that off!!!! A mild flapwheel, or maybe better scotchbrite, on a diegrinder, probably from above?

Chris

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yea think ill try the piston back in the bore first see what if any effect the rust is having..... then like you say remove it carefully from above

think il pull a couple main caps and just double check the bearings whilst this far in - and crack the rest of the big ends just double check bearings look ok in them

looks like gonna be tomorrow before I can get to it ;-(

remember when checking the big ends it's the rod side not the cap side that takes the load and wears more. the mains it's the cap side that takes the load so shows the wear. you probably knew that already but just in case :whistle:
neil.

Any news for us ?

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It’s all stripped rods out … not found anything really one of pistons seems to be more free to slide to and fro on pin than others but can’t feel any play but maybe is once hot? Better spend some time with family over weekend .. will measure up pistons mon and also ty and set up dial indicator and measure cam as blackpop says … I remember wrist pins were absolute pain to get through stock rods when put together.. wonder if I messed summin doin that …. Always wish I had put a set in with floatin small end .. can honestly say after owning this car for 28 years I have never been so disheartened with the f Ing thing

in other news the paint shop is hoping get some colour on body on mon

thanks again for all the advice lads

i wouldn't bother sliding that piston back in the rusty bore if the rust is sticking out into the bore. as above that needs carefully sanding back first. also as above piston slap is when cold, the piston expands when warm which could explain the knock if the rust is sticking proud of the bore surface. have you got a steel ruler you could hold in the bore (top to bottom) and move it round the bore over the rust? that'll tell you if it's proud of the surface.
you'll sort it soon enough though, don't worry :thumbs_up_smiley:
neil.