Converting wet crank to dry primary.

[CooperTune]

Awhile back I bought a large pile of old Mini mags. I enjoy reading them and looking at prices years ago. I'm almost sure I saw a section in one on converting wet tail to dry. I have no idea which pile of mags that may be in. The wet crank has 1.5 tail so a small bore primary works but there is more to it. Thanks for any help. Steve (CTR)

[gs.davies]

I looked at doing this ages ago. One of the Haynes manuals covers it - think it’s the purple one.

Basically and from memory, there’s a brass plug for the oil feed in the crank to fit and a deva bush primary gear. There was one on here a little while ago I think. Failing that, have a deva bush inserted into the original primary and machined to size. I was speaking to either AC Dodd or Keith Calver about that conversion.

I ended up starting to build a 1098 instead but now will fit a dry 848 (at least for now)

Good luck.

[Spider]

It's pretty much as GS describes above. The Pin was a Tapered Brass Pin (22A123) and was size such that when fitted, it should end up below the surface. Other than that's it's all just as you'd fit any other Dry Primary Gear.

[251 ENG]

I have a NOS primary gear for this conversion listed in the for sale section

[wild_willy]

The conversion also needs the correct backing ring to suit the dry primary gear as well. This backing ring is thicker to allow for the shorter dry primary gear.

[LuisM]

HI Steve,

this might give you all the details

Cheers
Luis

[850man]

A SU needle cut to size is perfect for blocking off the oil hole in the crank.

[mnicoop63]

I have been talking with a friend about this for the last couple days. I have a couple 997 engines and one is still wet and the other has been converted to dry. We kept going back and forth about what was needed so I removed both C washers, backing rings and primary gears. On the wet primary gear there is the C washer, the backing ring and then a notched spacer that fits with the prongs that stick out from the rear bushing in the wet primary gear itself. On the converted Deva bush primary gear there is the C washer, backing ring and then a solid spacer then the primary gear that has the top hat type rear bush. All the parts seem to be different. The C washer on the wet type is slightly shorter and the backing ring is thinner. Spacer is obviously notched and thinner. On the deva bush type the C washer is longer and the backing ring is thicker. The two C washers are not interchangeable between the two. The spacer on the deva bush type is considerably thicker than the notched spacer of the wet type. The wet primary gear is longer than the deva bush gear hence the different backing ring and thicker spacer. Overall the two assemblies are the same length. I think it was 3 1/4 inches.

The part number for the deva bush conversion backing ring is 12A671. This is for both 997 and early 1098 oil fed primary gears which were the same for both engines. From what I can tell the C washer used and backing ring are the same as all engines from 62 on. I am not sure about the 1098. I think it may have had a recessed washer at some point. It seems to me that part number 12A671 might refer to the thick spacer between the backing ring and rear top hat type bush of the deva primary gear. I am certainly no expert and could be wrong but this is what I have found about converting from oil fed to deva bush primary gear on the 997 engines. I am still confused as to the flywheels on these engines. The oil fed primary gears had an oil seal in the flywheel and I am curious if when the deva bush type gear is used is the oil seal just removed from the flywheel?

Lastly, I am wondering is the service bulletin above is for the oil fed 850 primary gears because the part numbers don't jive with anything I have seen.

[LuisM]

I have been talking with a friend about this for the last couple days. I have a couple 997 engines and one is still wet and the other has been converted to dry. We kept going back and forth about what was needed so I removed both C washers, backing rings and primary gears. On the wet primary gear there is the C washer, the backing ring and then a notched spacer that fits with the prongs that stick out from the rear bushing in the wet primary gear itself. On the converted Deva bush primary gear there is the C washer, backing ring and then a solid spacer then the primary gear that has the top hat type rear bush. All the parts seem to be different. The C washer on the wet type is slightly shorter and the backing ring is thinner. Spacer is obviously notched and thinner. On the deva bush type the C washer is longer and the backing ring is thicker. The two C washers are not interchangeable between the two. The spacer on the deva bush type is considerably thicker than the notched spacer of the wet type. The wet primary gear is longer than the deva bush gear hence the different backing ring and thicker spacer. Overall the two assemblies are the same length. I think it was 3 1/4 inches.

The part number for the deva bush conversion backing ring is 12A671. This is for both 997 and early 1098 oil fed primary gears which were the same for both engines. From what I can tell the C washer used and backing ring are the same as all engines from 62 on. I am not sure about the 1098. I think it may have had a recessed washer at some point. It seems to me that part number 12A671 might refer to the thick spacer between the backing ring and rear top hat type bush of the deva primary gear. I am certainly no expert and could be wrong but this is what I have found about converting from oil fed to deva bush primary gear on the 997 engines. I am still confused as to the flywheels on these engines. The oil fed primary gears had an oil seal in the flywheel and I am curious if when the deva bush type gear is used is the oil seal just removed from the flywheel?

Lastly, I am wondering is the service bulletin above is for the oil fed 850 primary gears because the part numbers don't jive with anything I have seen.

Good info, thanks!
and as you pointed the service bulletins i've posted refer to 850 thin type wet crank...22a520 is a thin type deva bush primary gear.

Cheers
Luis

[Spider]

Luis, thanks for posting up that TB for your new found collection, very kind.

I am still confused as to the flywheels on these engines. The oil fed primary gears had an oil seal in the flywheel and I am curious if when the deva bush type gear is used is the oil seal just removed from the flywheel?

Lastly, I am wondering is the service bulletin above is for the oil fed 850 primary gears because the part numbers don't jive with anything I have seen.

One other small but important item regarding the Flywheels used for Wet Primary Gears, if retaining them as wet is there is a thin paper gasket between the Hub of the Flywheel and the Flywheel itself. I've found it is worth checking these as a few I've checked the gasket has been rather crisp.

A later TB does say to remove and discard the Oil Seal from the Flywheel when doing the conversion. This is actually mentioned in Luis's TB above.

There was 3 Flywheels used with the Wet Primary Gear;- the 850 (thin tail) 22A129, the 1100 (thick tail) 12G96 and the 997 Cooper (thick tail) 12A377.

This is a parts list covering the 850 and the 997 engines. I'm unsure if the 1100 parts align with the 997, however based on what you've found above, it would seem so.



I'll also add here that I feel if the Wet parts are in good order and clearances are OK, then I feel it is a better arrangement than the Dry Tails. The issue with these it seems is the Seal in the Flywheel and / or the Gasket under the Hub. I know a popular thing to do for the seal is to use a Front Hub Seal, however, a Silicon Type (red in colour, like the usual Primary Gear Seal) with the correct Hydrodynamic vanes in the seal should vastly reduce the Oil Leak issues with them.