Hello,

I acquired a PAC Performance center bearing kit from a person in England. Now I was wondering what sort of fit the bearing carrier should be in the center housing. I asked pac performance multiple times but the best and only I got out from them was 'size for size' which seems a bit odd to me as then basically depending on temps or so the bearing carrier could be loose in the iron and the only thing preventing it from spinning would be the brass oil supply tube.

It will go in a 13B PP to relief the shaft a bit on a mis shift condition where it spins 10k+ for a few 100 msec.

 

it seemed straight forward to me; bore to the same size at the same temp, which is going to be a press fit. I would expect expansion to be approx. the same, but would use a lapping compound on it myself too. It would have to be a lot looser than that to actually spin, plus the bearings being seized/failed. The friction there would have to exceed the friction at the e-shaft face, which is smaller and likely has less surface area than the iron/outer bearing face contact. An interference fit could possibly result in a cracked iron is maybe why they do it that way.

 

Ok, I was thinking maybe one needed to use a mill and mill the hole so it has a tab that locks the carrier in one of the 4 slots. I agree the friction of the bearing would be small and it is normally not likely to start to spin the carrier but as you know also its a very dynamic something going on the there and if its a bit loose it could still start to rotate and eventually perhaps get loose. the brass tube has cut 1/8 threads which seem like a perfect source for a fatigue crack to start if it would be stressed just a little every cycle.

 

Ok so I finally machined a couple of center plates to accept the bearing. I aimed for about 5 microm interference fit .005mm so heat the housing a bit then it slides right in.

Next question is I see on the PAC website they offer the center carrier for dry sump and wet sump engines. What would be the difference behind that? I seem to have the 'wet sump' item and our engine is dry sumped.. my idea was that for dry sumped engine they forsee more area for the oil to flow back. In this case I could drill a couple of extra holes in the wet sumped item I have

https://www.pacperformance.com.au/13...ccentric-shaft

 

I don’t see where it states which is which? Did you get their input on that idea? Likely they’ll be the only source for the answer on it.

Got to think the price must be through the roof for that entire 2-pc shaft assembly these days.

 

No not yet. But logically id assume dry sump engine usually run more clearance and more oil pressure thus also more oil that has to find its way out from the rotor main bearings back to the sump

i think i am just going to copy their hole design in the carrier I have. Seems easy enough.

next this im thinkering about is how to cleanly make the oil feed for the center bearing. At the moment there is a brass tube with 1/8 threads with some thick piece of metal that one i suppose glues or welds or brazes to the center housing and then this brass pipe still has about 1mm play in the hole of this metal plate. So all in all it is a rather sketchy setup which might be improved upon..

 

I have a Green Bro’s 2-pc that is the same basic design sitting in storage, but I was told by a notable race engine builder that the Xtreme Rotary one was a superior design because it was fed directly by the engine oil system rather than using that pipe-feed arrangement

 

Dunno. I could drill a hole in the e shaft so it would get fed from there but that would reduce oil flow in the rotors and rotor bearings as the main bearing oil hole that feed the e shaft galley are quite restrictive

 

Ill add about 4 hole per side on the dots..

 

Made a slightly longer pipe w brazed on -4. It seals in the hsg with a rubber from a cable glant

 

finished product

 

I suppose better safe than sorry, but seems hard to believe that center notch isn’t sufficient to drain off fast enough, which I just noticed that the one they offer with drain holes doesn’t have the notches and are drilled straighter … 🤔
.

 

We drive rather big clearances and if you see oil fly into drive sump tank it seems like more then plenty for small notches. I estimate flow to be around 15-20 gallons a minutes at 150 psi oilp.

 

suppose I didn’t consider that it’d otherwise be fully open, got it.

 

Upon assembly it seems that the 2 pc shaft is 1mm longer then a stock item. Shaft becomes blocked



when stationary gears are bolted down.

think I will shorten the rear gear 1mm approx.

 

Shortened the gear. So far so good, shaft spins smoothly. Then assemble engine. Tighten tension bolts, then spins only like a bit under one revolution then was blocked.. not good




turned out the jets grab the eyes of the c-clip

ok grind them flush w shaft.

assemble again.. same lol





turns out the front piece has like a bump in the chamfered area which interferes with this tooth on the rotor. Oh well rotor has to live without tooth now 😎

 

Saga continues. When I torque down front bolt over 150 Nm the shaft fails to come down from its own weight when measuring end play. Even with front gear removed this happens.

not good. Maybe the cone where the halfs join expands making the front rotor journal out of round and jams the rotor bearing.

anyone had this before or knows what should be tightning torque on front bolt? On 20B is like 300 Nm but that feels like a beyound bad idea to try..

 

As suspected there appaered to be a slight mistake in the shaft finishing as the front rotor journal seems to have been ground without proper tightening of the the halves. With 200 Nm the journal was about 0.05 to 0.06mm out of round just at the edge where the cone starts. The front rotor bearing was also slightly oval and the tightest point was about 0.06mm clearance. This caused the shaft to become hard to slide upon proper tightening of the front bolt.

I ground the journal round again while being torqued to 200 Nm and now it spins totally fine when assembled.