crack in cylinder bore

[jono]

I would appreciate the insight of this noble forum.

I have just stripped a low mileage TC which is all on std bores and bearings. All bores pass the fingernail test and generally the engine looks to be good consistent with its mileage of 38.5k. The bottom end bearings look remarkably good - they are the original Ford items without the central groove and show little evidence of visual wear. The cam bearings have the usual scoring and will be replaced.

When I first took the head off wtih the engine in the car, the pistons all seeemd nice and tight in their bores except for Nr 4 which has a very noticeable 'slop' and could easily be rocked back and forth in the bore. I have now taken the rods and pistons out and no evidence of broken or stuck rings is apparent. Nr 4 piston does have evidence of wear in the skirt area and carbon deposits below the rings. The other pistons show similar wear but this reduces in degree as they go from 3 to nr 1

I have taken some preliminary bore measurements with a bore guage and all seem pretty much within original specification. I have unfortunately however noticed what appears to be a hairlne crack to the rear of cylinder Nr 4 more or less parallel with the adjacent waterway - the 'crack' is some 15mm long running down from the top face of the block.

I will obviously take expert advice on this and have the block properly measured and assessed, however I have two questions:


What might have caused this crack in a std and low mileage block? Is the block now scrap or can it be repaired?


What might be the cause of the loose fitting piston in Nr 4 when the bores otherwise show little wear and could this be related to the 'crack'?

Any other comments gratefully received


Many thanks

Jono

[gerrym]

Jono, did you ever see the engine running. This would have been your best guide to state of engine with respect to blowby or water pressurisation (combustion products detection).

If no to above question, you need to check everything and assume nothing.

To diagnose yourself what might be the problem, get a crack detection kit (see post on uprights) or.... I'd be thinking about a big thick sheet of perspex. Drill bolt holes through a gasket (as a template) and make a flat cylinder head. Same for front cover, check core plugs. Then pressurise engine block waterways to 15 psi. There should be no leaks. If you want to make it easier to see, add a drop of fluorescein dye (Screwfix has) which is used by Plumbers.

If it fails the leak test and you spot the dye coming through the crack, check with this Forum as to how to proceed with liner (assuming block can be saved).

Regards

Gerry

[rgh0]

Unusual to get a crack in the location you describe - it may just be a score mark. You need to do a die penetrant test or water pressure test as suggested to confirm its really a crack.

General a cracked bore is not worth sleeving as the sleeve can cause the crack to spread and the sleeve itself to fail due to lack of back support. I would look for a replacement block if cracked

cheers
Rohan

[gerrym]

Jono, as per Rohan's reply the fate of your block is resting on correct determination of this crack-like feature.

In your shoes, I'd be more determined to do the water test of the block. The clear perspex can be readily purchased from www.theplasticshop.co.uk and they will cut to size. It's also reasonably priced, eg a 20mm thick cast sheet which is very strong, 700 x 250 is around ?40

You can also use the same sheet for checking the cylinder head when you get to that stage.

Note, the 20mm is just a figure from the top of my head. Ask around for other's experience as to what works, you may be able to get away with a little thinner

[jono]

Rohan/Gerry,

Many thanks for your comments. I have good news after a closer inspection last night!

...it is not a crack, it was just an unusual fork shaped mark in the bore which was easily removed with a light emery paper I am a happy man now!

I have measured the top compression ring gap in the bore and it's reading 30 thou - a bit excessive me thinks Having measured the bore with a telescopic bore guage it reads pretty much within original spec so could this point to worn rings and could this account for the sloppy fit of the piston in the bore? (perhaps I am being to hopeful)

If I could return this low mileage engine to service with new rings and a hone I would be very pleased, I will however have it measured by an expert before I reach any firm conclusions.

Thanks again.

Jono

[gerrym]

Jono, lucky escape from a possible crack. Let us know how you get on with bore measurements and deciding whether rebore or just a hone is required.

Regards

[neilsjuke]

In the great scheme of engine parts the difference in the price of rings and new pistons makes me go for new pistons.
Neil

[gerrym]

I guess the most valuable things are now the blocks themselves: so every rebore avoided is a little more life conserved in the block. But overall it depends on the actual as worn condition.

Regards

[JJDraper]

As my block is on +60's I heartily agree with Gerrym!

Jeremy