Johnny Boost

I'm rebuilding my 13B that has over less than 45,000 miles on it.

How important is it that I have the side housings machined down so that there is no sign of previous usage?

PercentSevenC

Don't. Not unless you are planning on having it re-nitrided.

rxtasy3

iTrader: (2)

with only 45000 miles, unless something happened to cause damage, u shouldn't need to have them resurfaced.

j9fd3s

iTrader: (3)

from yawpower:

"Take the side housings for instance. The side housings are perfectly flat when new, or resurfaced, and the maximum allowable stepped wear is .0039" If you have a motor with stepped wear of .0030", you can say that it is still within spec, but 75% of it useful life is already gone! The motor may have run 75,000 miles already, but it only has 25,000 miles left before it is out of spec. And that is street miles! Racing miles are much harder on an engine"

the engine is torn down an wear is assesed, factor budget and then you decide how you're going to address the issue

there are basically two ways to treat the problem.

1. the pre 79 engines were not treated, when it wears, you just grind it flat again. in the us we like to do this with the nitrided irons too. the advantage is that you get a nice flat surface.

2. the japanese approach is to say that if the housing is worn out, you replace it. the mazda has an sae paper from 86 that talks about the nitriding process. the nitriding reduces wear and sliding friction by a lot. its also not very thick. so its removied when you lap the housing

they are both vaild techniques, lapping becomes more appropriate the rarer the housing is (if i had some crazy bridgeport irons, it would be more effective to lap, because to re-port, would be too much time etc etc). lapping is also slightly cheaper, irons are not that expensive when you get a good price.

Jeff20B

iTrader: (13)

If you don't re-nitride the later side plates after lapping, the iron is much softer than you'd want. This results is super-speedy wear of the oil seals and other seals on the sides of the rotor. It's great for shops looking to make a quick buck and produce repeat customers.

trochoid

iTrader: (6)

First question no one has asked is why this engine needs rebuilt with only 45k on it? Generally, with that low of mileage, resurfacing isn't needed. Measure the step wear and post the results.

Johnny Boost

Thanks for the replies. Much faster and concise than NoPistons.com gives.

Ok... well first off I over heated the engine and have a slight loss of compression in the front rotor housing. Also the front main bearing is shot.

I'll measure the step but could someone explain how to do this? I have some real nice calipers that will measure the step but I don't know what that really means nor how to do it. Little help?

djessence

Download the FSM, pretty sure there is a procedure in there.

Jeezus

iTrader: (4)

You might want to check your irons for warpage since it overheated. Lay a straight edge down and run a feeler gauge under it.

trochoid

iTrader: (6)

You'll need a dial indicator with a magnetic base to measure step wear, calipers won't cut it. As mentioned, it's all in the FSM on how to measure and spec engine parts.

7aull

iTrader: (2)

I think Pineapple Racing sells a dial indicator for about $70. When re-using my irons, Atkins told me just to go over the surface with an 80-grit sanding pad first....

Stu Aull
80GS
Alaska