currently rebuilding a FD 13b turbo engine, would like to increase the RPM limit , have been told that at high RPM the rotors can crash into the side plates, whats the best way to make more clearance to avoid this?

Use a lathe and very sharp tooling to remove .012" from each side from the tip to the outer oil scraper groove. Pad the jaws so no dents develop in the rotor. Only the tips will touch but doing the whole side is easy and quick. I have never bothered to rebalance anything after this but technically it should be done.



The rotors balance each other. The counterweights take out the rocking couple. If you then lighten the rotors on a mill, the rotating assembly must be balanced.



Break all machined edges with a small stone, and clean the rotor several times. Then take it to the car wash and use the high pressure wand. The little bits love to stay inside the rotor until you start the engine.



Lynn E. Hanover

Hey Lynn I never ask for these because I can usually visualize what you are talking about. But in this case could you post a picture of a rotor and shade or outline what you mean? I would really prreciate it.



Thanks in advance.

Sweet info, Lynn.. Thanks



I have been thinking about this for a while, but figured the rotors would need rebalancing.



*Grabs rotors, runs to the lathe*

Ah thanks mate, thats exactly what i wanted to know, have spent countless hours trying to google this info but couldnt find anything https://www.nopistons.com/forums/pub...IR#>/bigok.gif https://www.nopistons.com/forums/pub...IR#>/bigok.gif any other tips on modifying for higher RPMs? will be using rx8 bearings and stationary gears, PTS seals, cross drilled eccentric shaft, fully balanced rotating assembly, stud kitted instead of dowelling, was thinking is there any way i could line bore the engine?? like you do on the main bearings on a piston engine?

Sounds like you've got it figured out for the most part. You should also pay a lot of attention to the oil passage, they are horrible from the factory..

will be using a new oil pump, was going to look at externally feeding the rotors like they do on the 20b engines with an oil manifold, might not be needed though

If I hadn't lost my damn shop camera, I would post a picture of what we do. We don't use a manifold, but have the oil lines external...

oh that would be great if you could take some pics eventually https://www.nopistons.com/forums/pub...DIR#>/cool.png

The picture would be a rectangle or side view of any rotor. Your job is to make the rotor thinner than it is now by a total of .024" or .012" from each side. ( what you see in an end view, or the triangular shape)

is where the material is removed.



The crank shaft is quite flexible and allows an "S" shape to develop at high revs. This allows the rotor to tip at a slight angle between the irons and the part of the rotor around the corner seal hole will drag on the irons. So that portion that is likely to touch or drag is reduced by .012". You can remove material from the tip to inboard just an inch or so, or go right to the side of the scraper ring hole. Easy to get it the same if you go all the way rather than stop at 1 inch or one and one quarter inch.



I also remove about .005" from each thrust face that keeps the rotor centered between the irons. Notice that some overheat failures include irons completely hosed by the thrust faces touching without enough oil film?



(Big black circle around the center hole in the iron).



When you pick up a rotor with one hand, you thumb and fingers are on the surface that must be reduced.



If you still need a picture (as I often do) I will assemble one.



Note also that mods like this are not required for operation at or below the stock red line. (but what fun is that)?





Lynn E. Hanover

I've seen the rotors touch on rx-7s limited to 8k rpms.



I have my suspicions as to what caused it though...

great info lynn, does this have much effect on the oil scrapers? since theres .012" less on one side? interesting on the thrust faces i would have never thought of that https://www.nopistons.com/forums/pub...1047683894.gif much appreciated

No machining in that area at all. The grooves are left stock. The thrust face on one side is part of the timing gear. When you lay a straight edge across the rotor faces, the proud land area (the widest part of the rotor)is the thrust face. It seldom touches anything so many have no wear marks. Normally the side seal and corner seal spring pressure keeps the rotor centered in the space.



Lynn E. Hanover

Thanks Lynn.

cheers!

And again today, another engine which was limited to the stock s4 redline...

ive seen that too, we thought it was the gear coming out, although it could be oil pressure related too, stock 89-91 redline, 8250....



later with more oil pressure, we were revving a junkyard engine to 9400 with no troubles....

I forgot to point out that before measuring the thrust face, press the gear into the rotor solid.



If it has wear marks on it press it in. Then run a DA (orbital sander) over it to take out tooling marks and give it a dull finish, so touching will shine it up so you can tell when it walkes out again.



Or,



You can drill three holes that involve a bit of the gear and the rotor the tap size for a 6-32 socket end headless screw. Tap it and screw in a screw to the botom and stake over the hole. Gear never walks out again.



Lynn E. Hanover

Thanks a lot for the great tips Lynn!!! Now I gotta get these things over to the machine shop and make it happen.

This can happen on motors that run too hot. The bearings work on the principle of a hydrodynamic wedge. Being that these motors are always in the power stroke it is important(crucial) to keep that wedge. This will start to break down once the heat starts to get over 200 degrees. When that happens things start to move around in ways they shouldn't. That is where higher oil pressure combined with a adequate cooling is important over 4krpm. Not saying you not aware of this just putting the two statements together for others to read.





-S-

Should this be done when the rotor too housing clearence is allready greater then that reccomended by mazdacomp?

It depends on what you are talking about?



For the thrust faces, no. The racing clearance is fine.



For the corners of the rotor, that would not be the case unless the mod had been done already.

So, if its been done, fine, leave it alone.



Only required for engines that normally run above 8,500 for long periods of time.



If you normally shift at 7,000 and you miss a shift, it might go to 8,000 before you catch it.



If you normally shift at 9,600 and you miss one, ouch. You would need these mods.



With the mods and 100 PSI minimum oil pressure and racing bearing clearance, no problem at all.



If you miss a shift and scream the engine, take a filter can apart and look for bearing material in the paper.

If no parts in the filter material, screw on a new K&N and go again.



Lynn E. Hanover

Hmm, looks like i misread the mazdacomp site, It only has specs for land width and land protrusion.



Would you happen to know what total clerence we are looking for between the rotor sides (not the land clearence) and the housing?



Thank you.

Well,



that is a maybe question.



The reduction of the land area to get a bit of extra clearance there is in order to arrive at

(According to Racing Beat) .009" plus or minus .001" for 12As, and .010" plus or minus .001"

for 13Bs. That has to be the minimum total clearance. In this case the plus side of the spec means that more

material is removed.



The land protrusion is on the order of .003" to .005". So if you remove the .010" to .012" from the sides outboard of the land area the possible clearance when the rotor tips due to crank flex In theory will be improved by .020" to .024" total. To some extent the land area will suffer the same fate as the rotor tips and

and the land touches first. So I take off the additional material.



I have not thought about this in years, so I just measured a stock rotor against a rotor housing. I get exactly .010" total land clearance. Or .005" per side. So you can see that a badly overheated oil supply and just a hint of the gear walking out, will get you that black death around the center of the irons. Neather the gear face on one side or the cast iron on the other side makes a good bearing, and that superheated oil will not save the irons when the gear moves a bit and drags on the iron.





This rotor housing measured 2.756" and the rotor at the apex was 2.740" for a total clearance of .016".

Not much is it?



So, if you take off .010" per side you would get a total of .036" total and if you take off .012" per side you will get .040" total clearance.



If you reduce the thrust faces, measure the oil scraper lands as well, as in some cases they may be tall enough to touch first, and you don't need that.



For turbo engines (remember I know nothing about turbo engines) I would only reduce the rotor width right at the apex and stay within about an inch, so as not to expose much the corner and ends of the side seal to combustion pressures. Removing material also removes support for the side seal. (More of the side seal will be sticking out of the groove).



If you are not building an all out racing engine, please do yourself a big favor, and forget you ever heard of these mods. If you race you will loose an engine from a missed shift or early downshift. Clearanced or not.

.

The most I have seen turned so far has been above 14,000 RPM, and I only can tell you about that much because the Smiths flyball tach has no numbers where the tattle tale stopped. The fully (a lot) clearanced and lightened rotors touched everywhere. The bearings got shined up real good. The corner seals broke.



The engine ran again the next day after a rebuild in the dirt (my favorate thing to do) and with just a bit less oil pressure ran fine.



The driver attempted to make a 5 to 4 downshift after the long straight away at Road Atlanta and got a 5 to 2 downshift instead. With a Hewland trans it went right in and blew the bronze lining off of the clutch disc.

But there was enough left to spin the engine up to God knows what.





Lynn E. Hanover