crankshaft journal sizes-do I need a regrind

[Joost_Pompert]

Hello,

This is a bit of a technical query for someone with the mechanical know-how on engines. I am rebuilding an 10MA engine at the moment, as it badly needed an overhaul. I have stripped it right down, and am debating whether I should get a reconditioned crankshaft or whether I can make this one last with new bearings, for another say 20k miles. Part of my reservation will be sending it by mail to the UK (I'm in the FAlklands), and getting another or same one back, postage for that weight will be quite high. Anyway, so I have measured all carefully with a micrometer, and found that the measurements do not differ vastly from the stipulated values: 44.46-47 for main journals, and 41.28-29 for crankpin journals.
my journal sizes are:

Measurements were taken six per journal, starting at the front, then middle, then rear part of each journal

main 1st: 44.42-43, 44.46-47, 44.43-44
main 2nd: 44.43-43, 44.47-47, 44.38-46
main 3rd: 44.40-44, 44.47-47, 44.41-46

the main bearings were worn coppery on the inside, with on some sides even the copper worn down to the metal layer underneath. Some very minor scoring noticed, best described as scratches rather, but perhaps best explained by the difference in values (44.46-47 in centre of journal, and around 44.42-43 on edges

same as above, but bearings hardly worn at all.

crankpin 1st: 41.26-21, 41.26-28, 41.27-28
crankpin 2nd: 41.26-29, 41.23-28, 41.24-29
crankpin 3rd: 41.28-28, 4126-29, 41.27-28
crankpin 4th: 41.29-285, 41.28-29, 41.22-23

I'd appreciate an expert opinion on whether this should be considered for a regrind or leave it until in five years time perhaps.

Thanks,

Joost

[bmcecosse]

I think you will be fine with new bearing shells - do also check the oil pump is in good condition, or fit a new one - and make sure the oil filter is working as it should - and the plate under the filter element has not been thrown away at some point in time! I have to ask though - is yours the ONLY Minor in the Falklands??

[Joost_Pompert]

Thanks for your reply, yes all other parts will be checked also of course, but knowing what is needed on the crank is the essential first step. Next is assess whether I need a rebore or not! And yes, mine is the only one running at the moment. There is a 1963 green saloon sitting in a yard, awaiting repair, and a 1933 mm sitting in a garage, awaiting someone's retirement to be done up. That's it. 4x4 country!

[bmcecosse]

I'm sure Prince William will be happy to carry you out an exchange crank and other other small parts you require in his hand luggage - if you promise him a drive in your car.......

[IslipMinor]

Taking your smallest diameters for both mains and big-end journals the wear is 0.003" or 0.08mm, which is really too much for just new shells. In particular the main bearings, which you say have worn through the both the bearing material and the copper layer, through to the parent steel bearing shell.

You would certainly 'get away' with just new shells, but I would expect some crank rumble on cold start-up, as the oil could well drain away whilst the car was not being used. This then aggavates wear and you could well be back where you are now in less than 10,000 miles - but on the Falklands that is quite a lot of motoring!

If you do choose to go the 'shells only' route, do make sure that you fit a new oil pump, as the current one will have been circulating lots of lovely steel swarf from the main bearing shells!

Whichever way you go also make sure that you thoroughly flush out all the oilways in the block, crankshaft, head and rocker shaft, and obviously clean the sump and everything inside the block very carefully.

[bmcecosse]

Yes - it's not ideal, but given the circumstances I think it will be fine !

[katy]

Are bearing shells .001" oversize available for these engines? If so that may be the way to go.

[bmcecosse]

No - just standard sizes........ I used to make bearings at Glacier - imagine the work to make bearings like that! 1 thou is not important - in fact competition engine are built with extra clearance in the bearings - this is not a problem provided there is sufficient oil delivery to the bearings to maintain a hydrodynamic wedge of oil for the bearings to run on.

[Joost_Pompert]

Dear All that have replied so far.
Thanks for your suggestions and opinion. In an ideal place I would get a reground crank, so my question was really how far you can go with the wear (in Main bearings ~0.08mm max), since the regrind sizes take it down ~0.25mm. But you are right, 10k goes a long way here, I have done around 24k in the machine in the six years since 2005, but I had noticed the deep rumble at startup, and poor oil prssure at times, so i know what was going on. I just expected it to be worse than it was, but I think I will battle on for now with new bearings. A new oilpump will be fitted, as well as other parts, and depending on bore wear probably a rebore and oversize pistons. If William wants to come for a ride sometime he'd be more than welcome. I see him fly past a few times week in his yellow SAR machine, and he lands close to the hospital with injured fold, but other than that his visit is low-key!