K55 rebuild questions

Emmick93

Member
I am rebuilding the bottom end of a K55 and had a couple of questions. When installing the new crankshaft bearings, should the back side of the bearing cage be facing the inside of the engine or facing the case bore? I noticed when I removed the old bearings, the cage back side was facing the inside of the engine. This seemed backwards as I would think it would be best to orientate the bearing placement that more exposes the bearing balls to the fuel/oil mixture for increased lubrication. Perhaps it's not critical but wanted to check first. My second question is with regard to port polishing. I noticed that the transfer ports had been polished, but the intake track (right after the reed cage) was left as-cast. I was curious if you had thoughts why this surface would not had been polished? Was this a tech ruling back in the day when these engines were being raced? For best performance, I would think that surface should be polished but didn't know if it was best to leave as a rougher surface to improve fuel/air mixing. I am using the engine for track day fun only so no spec restrictions. Thanks for the advice.
 
I was there when they first came out. I'm pretty sure IAME built that engine in response to the new USA built LMR (Lamello/Margay/Racer).

If the bearings went bad early, you may be right. Have you checked the run the crank? Are you going to break the crank down? How many hours on the engine?

I'm pretty sure, if you ran that engine in a stock class, you could not do any of the modifications you're talking about, such as polishing, etc.
 
Emmick93,

In my opinion, the lube to the bearings comes from the back side (fuel/oil "puddles" in the transfer passage in the case and runs down the hole to the bearing). That said, I have *never* found a difference in bearing life running them either way. I choose to put the more "exposed" side toward the center of the case because it makes it much easier to inspect the bearing condition, should you have the engine apart and are undecided about replacing them.

Believe it or not, I have always kept a relatively "rough" texture on any port that has air/fuel mixture going through it (intake port whether it's a piston port, reed or rotary valve) and all the transfer passages. The engines I've had just seem to run and carburate a touch better if the "fuel" passages are not polished. I personally chalk it up to avoiding something like the way steam beads-up on a mirror (which is of course a very smooth/polished surface).

The only thing I personally polish is the exhaust port, as that definitely lowers the amount of carbon buildup.

PM
 
Polishing- some builders did it (ok) but IMO it is much better to keep certain areas roughed up; helps atomize fuel, oil puddling at transfers etc. as Pete stated, best port to polish is exhaust as this is where you want flow to really count on the back side. I have never found a difference in how you put the main bearings in except depending on how open the cage is per manufacturer ie: SKF, Koyo, FAG etc. one thing know one has touched on is the lubrication holes. If rules and specs allow...is swept angle/chamfer/slotti and hole size for lubrication.

intake track roughed (reed engines), transfers semi smoothed and match ported for optimal. And exhaust smoothed. Combustion- polish the crap out of that chamber.

bearings- personally open face towards crank (inward). My opinion on this is also based on above and/or addition of shims for crank float. The shims can kinda close up the oil slot a bit but the bearing cage on that side also helps create a “vacuum” if I can call it that; and help pull/disperse oil on the back side of and through bearing with swept volume. Sounds a bit technical but it’s not.

Air compressor-air in/air out + efficiency =HP
 
Thanks for all the professional advice. I installed the bearings with the open side toward inside of engine. I have the cases assembled and all looking good. For the Motoplat rotor lock nut what torque is recommended? Should grease be applied on the taper to protect against any corrosion and aide in future dissassembly? Thanks
 
I personally always make the taper (and tapered bore in the rotor) "clean and dry" for assembly. Do you have a puller for the rotor?

PM
 
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