998/1098 primary gears are not interchangeable with 1275 cranks, but I've never had a problem with any 1275 primary gear with any flavour of 1275 crank.

I see a lot of discussion on the forums about the 12G1505 cranks, apparently there were variations.  

https://www.calverst.com/technical-info/crankshaft-standard-production-crank-identification/

https://mk1-forum.net/viewtopic.php?t=28752

below is the only discussion I found where  a difference in primary gear was mentioned:

https://mk1-forum.net/viewtopic.php?t=38106

in the unlikely event that your engine is an unmodified original, your 1978 primary gear would not have the dust shield which began in 1979, see illustration here:

https://www.somerfordmini.co.uk/catalog?cPath=100680_100851_100863

A series primary gear had 24 teeth, later A+ had 29 teeth.  What do you have?

If previous owner put a late motor on an early gearbox, they needed new gearbox input and idler gears to fit the later primary gear, or put an early primary gear on the newer crank.  What gearbox do you have?

Be advised, Minis got modified all the time.  It is not uncommon to find a 998 primary gear that was bored out to fit a 1275 crank.

https://mk1-forum.net/viewtopic.php?t=31193

One reason to do that was to save a worn crank, have the crank journal cleaned up and then bore a 998 primary to fit it.

The 1275 A and A+ crank tails are all (supposed to be) the same, meaning if unmodified you should be able to swap 1275 primary gears from one 1275 crank to another.  What is the crank tail diameter of your 1505 crank at the inner journal ?

I'm new to classic Minis and forums in general. I don't know if it's appropriate to reply to such an old post but I need some help

Last summer I bought a 1978 Mini with a 1275 engine. After 1700mi a thrust washer failure destroyed my original 12G1505A. crank After reading everywhere that a CAM6232 should drop right in place of a 12G1505A I bought a used CAM6232 on eBay.  But now that I have it I discovered that my primary gear doesn't fit on the 6232 crank due to a 1.625in diameter shoulder on the rear end of the crank. It seems I need to either grind the step down to 1.500in diameter or get a different primary gear. Any suggestions? Am I correct in thinking the CAM6232 is the A+ and the 12G1505A the A (pre-A+) other way round?

Thanks for any help

In answer to your question I'll have a look when I get to the shop. I'm getting very low on cranks and have a couple of jobs pending. I'm not sure what they got in OZ but over the years I have stripped several AA auto units and found small journal cranks and rods. Lots of AA autos failed low mileage due to not changing oil often enough. That with the with the lower shock loading due to torque converter rather than clutch they don't crack as bad. I will tell you one season in a vintage racer and they should be crack tested. I cracked two running 1 hour enduros. At the Jefferson 500 we won our class and made the podium on a lap by ourselves two years in a row. As a young buck I was RPM crazy and loved the sound of anything above 7800. Steve (CTR)

ARP hardware is already installed and the shop I bought my pistons from installed them and checked over the rods for roundness and true.  They also line bored the crank journals.  I'm not sure what thrust washers are in it, I can't find my notes on those.  Only the bearings that I put in.  My recollection is that the thrust washers were within spec, and I didn't replace them.  They must have been oversized.

The lapping of the plunger sealing surface is not a bad idea, and I can see how that could contribute to oil draining back out of the pump.  This is not an every day thing BTW, it's after a month of sitting.  Still, it never used to drain out unless it had been sitting for 8 months with the previous pump.  What would have changed with the seat between then and now?  There is an underlying problem of low oil pressure under normal spring pressure with a plunger, and I still think that is due to a worn crank.  I've significantly boosted my oil pressure by using the 9/16 steel ball, and packing a spacer between the spring and the cap on the block to increase spring force, and it is not a problem, however if the underlying issue was fixed via a new crankshaft, new oil pump or?  and I left everything else the same, I'm sure my oil pressure would shoot through the roof.

I'll go ahead and lap the plunger seat because as you said, there's nothing to lose, and maybe that will correct the oil drain back issue.

Craig

I've been thinking about this thread all day and half of last night. I'm starting to think perhaps you could have an issue with your oil pressure relief valve seat. (and yes, I heard you when you said you had the ball bearing thingie in there) Hear me out:

you have no oil pressure at startup as if you have oil drainback somewhere in the system-- which is why I suggested it might be oil pump-- crack and scores would cause the pump to become un-primed. But the oil pressure relief setup could do the same. The oil on the pressure side should be full pretty much from the takeoff banjo on the front of the block all the way into the oil filter. This should not drain away. But the oil that is insid the block between the pump and the banjo union could be bleeding off through the blowoff valve/pressure relief setup. 

This also happened to me, I believe: A fresh motor with tight tolerances, new pump, but poor oil pressure when hot, especially at idle. A friend suggested we lap in a pressure relief plunger to the seat that's in the block. He used a stick with tape to wedge the plunger onto it, then used valve lapping compound and lapped in the seat to get it round again with an even sealing surface. He cleaned it out as best as he could with rags and brake cleaner and so on and then we also did a crankover using the oil to push whatever's left out onto the garage floor/driveway ... or... catchpan if you will.

It worked! I went right back to using a ball bearing instead of the plunger after a month or so and this motor has never had an oil pressure issue since.

That's an easy try with the engine still in the car. Give it a shot-- not much to lose.

OK, so what thrust washers does this engine have? 

Craig,
An AA auto crank is the same as the 12G1505 one you have now. However, ex auto cranks seem to generally not be cracked, as they saw a lower rpm ceiling in service than manual ones did.

re your AA rods, they will be fine in a road car. Just check them for rod eye size and straightness. And fit ARP bolts if not already.

Thanks,  I posted the specs of my rods and mains for confirmation of the type of rods I had.  I wasn't completely sure.  I do have the AA rods, but lightened them by removing the excess material, so they are about 1/2 their original mass.  I'll either start with the oil pump, or just do the whole thing.  I know that the crank is completely worked over, so I'm just driving it out at this point.   So, tell me about this AA Auto crank?  How is it different than an A+ crank, will it drop right in, and is it for sale?   

Craig

i agree with Spank. This sounds like an oil pump issue, and could be confirmed with about a day of work. As the market for mini parts expands and falls to bits throughout the world,  a new part can be more of a liability than the part you are replacing.

As Kevin posted those would not be S rods. Cooper S rod journals std measure 1.625. If the rods you have are AA rods ( ones with large square metal balancing block on cap ) I'd consider replacing them with A+ type rods which are much lighter and better built. I also save all oil pumpsin case I need a shaft. Some of the old pumps had a key in the shaft and I broach a keyway into the rotor and hone the bore for a lighter press. If no key I'd drill a .125 hole between rotor and shaft and press a pin in place. I have a set of new in the box upgraded material A+ rods on hand. Bought them for a job then went small journal instead. Let me know if interested. As far as that goes I have the AA auto crank freshly ground 10/10 and plenty S rods. I also have a set of race prepped ( by MED ) A+ rods lightened floated and bananced. You would need to get a set of buttons. Steve (CTR)

You have big journal rods. NOT S rods. Grab an A+ crank and they will fit fine.

I misread it as non A+ non Cooper S...

Did you have this happen to recently installed oil pumps?   Mine probably has less than 4k on it.   My cam is a pin drive and oil pump has the longer Cooper S shaft (very rare and expensive), so I pressed my pin drive shaft from my old oil pump into the new slot drive pump.  It went in tight, but was a normal press fit.  Aside from that 'mod', everything else assembled normally.  Maybe these new pumps are poor quality with loose tolerances?

If you feel the need to do anything, pull the flywheel housing cover and put in a new oil pump. It's been my experience that no pressure at startup is because the oil pump itself has gone dry. Once it was because it was cracked, the other times because it was all scored to hell.

Replace the oil pump and gasket.

When I had it out I measured my rod journals at 1.73" and mains at 1.96".   Minimum on mains is 1.98" and minimum on rod is I believe 1.7".

Steve you can idle at 650/700?  Sign me up for that!

Well now we are getting the info we need. If you have small journal rods you will need to have the crank ground .125 on the rods and use the .030 thrust. Sound like you have clearance issues. My 1360 Cooper S block has an AA auto crank with small journal rods. OP is good and drives me crazy. At a warm 650/700 idle the needle bounces between 40 and 50 mech. Smiths. Blip the throttle and its right up to 60. At 70 mph turning 3000 it's 55 and at 90 at 4000 is back up to 60. Porsche has two pressure relief valves to maintain 60 psi. 

Looks like you need a crank with small journals of a set of A+ rods. Of course you can have a big journal crank turned but it's not cheap cutting that much. Steve (CTR)

Engine has S rods and oil pump was replaced when motor was out.  oil pressure when hot at speed is still close to 50 psi, so I'm not too concerned, but it has never drained out so quickly (after a month or so of not starting).  I think that's the loose crank bearing clearance.   

Does the engine have S sized rods or 1300 rods? Was this a new oil pump at the time of the last assembly? 25 years ago it seemed there were a lot of poor quality oil pumps sold, I had one of these disappointments. You did not say what your oil pressure was at speed when hot.  While I grew up thinking that high oil pressure was a must, that summer of 1991 I did thousands of miles at horribly low oil pressure and when I got in and changed the pump the bearings looked just like bearings.  Like, Spank would pay the postage if you sent them to him.  In any case, your crank originally had the large big ends and if still large, they can always be ground to S size big ends.  As a bonus, you could mess around with the stroke just to confuse anyone who might get in that engine after you!