Bearing & conrod shell measurments for a Spit 1500 engine?

No easy way to check a curved thickness. you need to check the clearance between shell and crank, this can only be done using plastigauge (expensive and tricky to use).

If the surface is in good condition and you think the shells match the crank then put them back, they are probably ok

mrcheerful

end bearing shells. What's the proper thickness & minimally

There is virtually no wear allowance for shell bearings, if that is what you are referring to. Or, to put it another way, if any wear can easily be measured, the shells are scrap. You can measure their thickness, using a ball attachment on a 1" or 25mm mike, or by using the mike with a short length of diameter on the inside of the shell. A dowel, roller, or short piece of silver steel, would be ideal. The shell should have a consistant thickness around it's circumference. Any variation more than about half a thou, and I would say they're worn out. I would also suspect the crankshaft needed a regrind. Mike.

If you've got the engine that far stripped and there is ANY doubt, replace the shells. It's not worth the risk for a relatively small outlay. John

IMHO, it's never worth simply replacing shells. Get the crank re-ground too. That doesn't cost *that* more than new shells, but brings things back to new.

I really believe it depends on the state of the crankshaft journals, as to whether new shells should be fitted. When I stripped my wifes 948 cc Minor engine at 80k after it had had a

0.020" regrind, there wasn't any measurable wear, so I simply replaced the shells. About 45k miles later, the car had a shunt severe enough to bend the front engine plate carrying the engine mounts, so I stripped it to check the crankshaft and block for cracking before replacing the plate. The crankshaft journals again showed no signs of wear, so again, I simply replaced the shells. I must admit that I was surprised, as the car has never been driven gently. 60-70 mph on NSL roads and the m/way was the norm, rather than the exception. I can only assume that regular oil changes at between 3 - 4 k has something to do with how well the crankshaft journals have worn. I would say that if the journals have less than 0.001" ovality from nominal, a new set of shells is all that is needed. Mike.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Plowman (News)" saying something like:

If the journals aren't worn it's a waste of time and money. On some engines (the Essex, for example) replacement shells are pretty much a service item at around 60-80K miles. I've done a couple of them and found the cranks to be fine and new shells restored oil pressure nicely.

This mirrors my experience of industrial and traction diesels, where the shells are recommended for replacement (subject to crank condition, of course) as a matter of routine.

For the early '60s Fiat twin cam it was recommended (in the Fiat workshp manual) that best life would be obtained by swapping shells at 25K and not regrinding until 75K or 100K (the cam belt was also getting swapped at 25K). This was an early example of a nitrided crank and certainly did last well - I've very rarely had to regrind one, only at around 150K.

OTOH, isn't the Spit prone to the thrust washers failing and the journals going barrel shaped ?

If the crank measures up ok that's really a pointless exercise and not that cheap. Depending on where you live and if you are in the trade or not it's still £50 to 80 to get a 4 cylinder crank reground. At least as much again as a complete set of shells and thrust washers. Why double the cost of the job if it isn't needed?

-- Dave Baker

Andy Dingley realised it was Mon, 16 Jan 2006

18:42:42 +0000 and decided it was time to write:

Yep. And the shells don't last too long, either.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Dingley saying something like:

Even in the early 60s when the average yearly mileage was lower, I wonder how many owners got that done every 25K.

Callard and Bowsers: Makers of Crankshafts.

Because on the *average* classic I've yet to find worn bearing shells and a perfect crank. Modern cars with tufrided cranks etc may be different.

Although I replaced the shells on my wifes MM, the old shells were not noticeably worn. I daresay I could have put them back, but having stripped it that far, fitting new ones seemed a sensible precaution. The crankshaft though was near perfect. All journals were nominal, with virtually no ovality. A regrind would have been a waste of money. apart from reducing the possible life of the cranskhaft. ATM it can still take 2 more regrinds before it would need to be replaced. Mike.

Well, maybe, but why strip down in the first place? ;-) In the old days when engines wore out I've never found one where bores/pistons needed attention but the bottom end perfect?

It would be some classic that got through 4 crank regrinds. ;-)

The engine and g/box was out anyway, whilst the body had a major rebuild. I gave it a rebore, new rocker shaft, with reconned rockers. Valve grind etc. Gave it a new timing chain, with a Marina front engine plate and timing chain cover that has the spring loaded timing chain tensioner, left the std rubber bands on though. I also fitted a Viscostatic fan from a Viva. Still sounded like MM engine, but with none of the fan noise of the std engine, or the timing chain rattle of one that's done few miles. I've still got all the std parts though, in case we ever want to make it original.

In the old days

It was a working classic. Used every day, up to a couple of years ago. Regularly taken on trips to Norfolk and Devon, (relatives) plus a couple of european tours. Driven the way it is, or was, (It's not on the road at present) 80k seemed to be about the norm for a rebore. Crankshafts seem to last much longer. The car is a '57, and we've had it since 1972. 70k on the clock when baught. Around 350k at present, on it's second engine, and the crankshaft should only be ground to a max of 0.060" u/s. Mike.