Drago86

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

Lynn E. Hanover

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

Drago86

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.

Lynn E. Hanover

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