#8 nosecone bearing OD - doesn't fit nicely into the case

[stownsen914]

I'm a little confused. I bought a new # nosecone bearing as my old one was showing moderate signs of wear. I noticed that the new one doesn't drop nicely into my crankcase half. The OD of the bearing is 65.05 mm. The case halves measure about 64.9 mm (measuring with case halves separated). Should I be surprised at this? Should it be necessary to massage it into place?

Then I measured the old #8, and it's also just over 65 mm.

[Henry Schmidt]

Originally Posted by stownsen914

I'm a little confused. I bought a new # nosecone bearing as my old one was showing moderate signs of wear. I noticed that the new one doesn't drop nicely into my crankcase half. The OD of the bearing is 65.05 mm. The case halves measure about 64.9 mm (measuring with case halves separated). Should I be surprised at this? Should it be necessary to massage it into place?

Then I measured the old #8, and it's also just over 65 mm.

You didn't list the type of case [aluminum vs Magnesium] but when you bolt the case halves together you'll fine that the bearings journal is not round.
Mag case are always oval top to bottom is larger than side to side.
I have also seen aluminum cases as much as .015" out of round.
Small amounts are not especially critical [that's why we measure the ovality] for excessive distortion and if minimal, we glue the #8 bearing with ThreeBond 1211.
I know: who in the hell wants to glue an o-ring seal? Answer: someone who really doesn't want to do the entire assembly all over again.
Keep on mind that over sized bearings are available but get the journal bored is challenging.
I am building a line bore tool that will allow for a #8 bearing bore option.

[stownsen914]

Thank you, Henry as always. It's an aluminum case. I guess I won't worry too much about the case being out by a few thou. I do intend to seal/glue the nosecone bearing as you suggest.

As for encouraging the nosecone bearing into place, is it sufficient to just let the nosecone bearing seat itself as the case is bolted together?

[Neil Harvey]

Be careful how you go forward. There are no shortcuts here and none should be taken.

When it appears the front bearing sleeves does not fit, that needs to be confirmed by measurement. All other effects eliminated. Dirt, glue and dowel pin fitment.

Some basics. The front of the crank moves the most. At engine speed, the front of the crank behaves like a pool noodle. The front bearing sleeve does not stop this. The crank moves, the sleeve moves, and the front of the case moves.

Measure the sleeve OD, then measure the housing bore. Alignment is difficult. Here is how we do it. Others may have another or better way. We have alignment sleeves that takes the place of the countershaft and bearings, same for the front sleeve. These are fitted to the case after the case parting lines are cleaned and lapped. These two alignment sleeves align the front of the case. Then the front lower 8.00mm stud is removed and we insert a hollow dowel in place of the 8.00mm stud. The hollow dowel can then have an 8.00mm bolt fitted to hold the case together. Once the front dowl is fitted, the case is split slight, and the front sleeve removed. The case retightened and the main housing bore measured including the front bore. Size and alignment can then be checked.

We have been line boring these cases for a long time and we have found this is the best way to measure and know. To fit the front sleeve without checking its fit is the wrong way in my opinion.
If it's the correct one from the case housing bore, maybe the bore is misaligned or out of round. I have read many posts where the front O ring appears to leak. Maybe for the same reasons.

Something else to note. We have seen on many if not ball Magnesium cases, the front bore has a wear groove where the O ring has worn a groove in the bore. This is how much the crank and sleeve move, and with an amount of force to cause.

Sleeves do fit and do not leak when all necessary work is done. No shortcuts.

[PeteKz]

Henry, or Neil, when you use 3-bond 1211 around the nose bearing, do you apply it inside the O-ring, or outside the O-ring, or slather the whole thing with sealer?

[stownsen914]

Pete - see the last page of the thread below, where a couple builders weigh in on the topic of your question

https://forums.pelicanparts.com/911-engine-rebuilding-forum/284737-complete-engine-sealant-thread-38.html

[PeteKz]

Thanks.

[Neil Harvey]

Originally Posted by PeteKz

Henry, or Neil, when you use 3-bond 1211 around the nose bearing, do you apply it inside the O-ring, or outside the O-ring, or slather the whole thing with sealer?

Dry. Maybe some silicone grease on the O ring, only. What purpose does the glue do?

The O ring is there to seal. The housing bore needs to the correct dimension, round and free of any dirt or damage. If not, fix it.

[Henry Schmidt]

I caution the application of "perfect" rebuild ideology. This ideology has you plummeting down a slippery slope into unnecessary spending.
These are old pieces of crap that will work well if you simply apply reason.
The sealant is a safety net in case your parts aren't perfect.
BTW: only a fool believes in perfection. Measure your parts as well as possible and account for imperfections in your measurements and thermal dynamics of a 40 year old case.

When Neil has built a couple more air cooled engines he may start to understand the necessity for innovation.