Hi, I had all of my irons lapped and I put my motor together today and checked the endplay. I am at only .001 end play. I would think that after lapping the irons that I would have a looser end play? Am I thinking wrong here?

 

Lapping the irons wont have any effect on the endplay. Endplay is controlled at the very front of the engine by the thrust bearing assembly. All lapping the irons will do is slightly alter where the eccentric shaft runs....not the freeplay.



Chris.

 

Thanks for the reply however I disagree with you. When you lapp the irons you are shortening the stack so end play has to be effected. I thought it out and I am almost 100% sure that lapping the irons would cause a tighter end play. Can anyone else confirm this?

 

As the world champion at using irons that have been surfaced way too many times, and should have been thrown away, allow me to confirm that it is possible to affect end play with shortened irons.



First let me confirm that end play is controlled (normally) only by the length of the spacer between the two hardened washers that rest against said spacer. One washer is thick and has a chamfer to accomodate the radius on the front of the crank. The other washer is thinner and sits in a pocket in the front counter-weight. The thrust plate sits between the two washers, and the needle races run against the front and rear washers. So, the spacer length controls the end play of the crank. Looking for .0025" to.0035". Use the larger number if you tend to scream the engine, as crank flex will use up more of your end play.



But suppose you have shortened all of the surfaces. That means that the front end of the rear main bearing is closer to the front main bearing and thrust assembly. So, for example, let us say you ground off .007" off of each iron. Now the rear main and stationary gear is .028"

(4 irons times .007"=.028").



Normally this results in the rear main bearing running up onto the radius on the rear crank throw. This can make the engine stiff when trying to turn it over. Left alone, the front end of the bearing will fail.



All cranks are not the same. Some are a few thousandths longer than others. All main bearings are not the same. Some are a thousandth or so longer than others. I just assembled a IT engine and had this problem with all new parts. Sometimes mains are set just a hair too deep and so on.



I discovered that the rear stationary gear was .022" too tall. I cut the rear gear down in the lathe. How did I discover this problem, you might ask? Because the end play did not increase when I installed a longer spacer. So, the thrust distance was being controlled between the front thrust bearing and washer, and the front of the rear stationary gear touching the back of the rear throw.



I have run into this before, so I loosened the rear stationary gear bolts and raised it up out of the rear iron a 1/16" or so. That way it could not affect end play. Shazam! the end play was now correct at .025". So I shortened the gear.



I have run into this at the track as well. Not on my car but on others. With the engine still in the car, just make up a gasket looking thing to match the back side of the front stationary gear out of a sheet of gasket material or out of the side of a beer carton. Cut into two pieces and slip it under the front stationary gear and put the bolts back in.



So, now you have moved the thrust assembly forward the thickness of the gasket. About .020". Now you have the full end play you need, and nothing is touching the crank anywhere.



If the engine is still on the stand, its an easy fix. If just the bearing is touching use a knife blade to scrape a small 45 degree angle right at the end of the shell. If the rear gear face is touching the crank, add the gasket to the front stationary gear. If you need more space, add one under the rear stationary gear as well.



If you cannot get the correct end play using a magnetic base on a dial indicator set, Go over eveything again.



It is like riding a bicycle. You can't do it, you can't do it, then suddenly you can do it, and you wonder why you could have have had trouble in the first place.



Lynn E. Hanover

 

I knew it had to effect end play as also the front stationary gear is housed in the front iron and now that the front iron is lapped it is moving the front stationary gear closer in thus moving the large center thrust plate closer to the front thrust washer causing a shorter end play right?





Lynn, I have .001 end play right now and the engine moves freely. This is the first time the irons have been lapped and RB swears that I am not going to have to ground down my rear stat gear. All this being true, can I just machine .0015 off of the spacer that I have on my lathe to give me a total .0025? Note: the spacer that I have is 8.0mm and is the shortest one available.

 

Nope.



First, the end play is a function of the thrust assembly. You can adjust the end play with just the thrust assembly and the crank. Any crank. Or if you do a lot of them you can just cut the front off of a crank and make a nice little stand for holding the crank nose straight up on a plate so your dial indicator can work. Once you have the thrust assembly installed on the crank nose along with the slinger (if any) and chain sprocket and distributor gear, and the front pulley, torque up the pulley bolt to 90 or 100 pounds, whatever you use. It is supposed to be about 75 pounds, but the crank is weak right at the first radius, and over tightening the bolt, makes everything stiffer.



You can weld a crank nose to the plate and drill two holes in it on opposite diagonal corners, so you drop in two case bolts (old ones) so the plate stays in place on the bench while you torque things up. Note here that increasing the torque will eliminate about .0005" of your end thrust. So only measure things with your full torque on that bolt.



The thrust plate is bolted onto the front stationary gear with the same bolts that hold it in place. That relationship never changes.



However, the remaining irons and rotor housings move forward the amount of the missing material.

And that is how you can have a problem. Racing beat does not take off much material at all, and may only have lapped the irons, rather than grind them.



Write this over your bench: Longer spacer=more End Play. Shorter spacer=Less End play.



This is where you have gone wrong I think. If you have .001" with the assembly torqued up, you need a spacer that is at the least .0015" longer than the one currently installed, to get to .0025" of end play.



Lynn E. Hanover

 

I f'd up. I mean can I just get a spacer that is .0015 longer so that my end play is .0025? And then if doing this and my end play does not change then like you mentioned above I will have to mill my rear stat gear correct?

 

Perfect, this answers everything I was spacing out about. You are the man!



Thanks again, you have helped my out too many times to count on this first rebuild.

 

Well, it sounds like a spacer problem, but if the end play will not change, I would ink up the front end of the rear main bearing (where it might run up onto the crank radius) and the front end of the rear stationary gear teeth. Bolt in the rear stationary gear. With the thrust assembly torqued up, Put the front of the engine up and rotate it through a few times.



Remove the rear main and look at the ink marks. If none of them have worn away, there is no problem with SES. (Short Engine Syndrome).



If these irons have never been ground or lapped before this trip to Racing Beat, I think it is just the spacer being too short.



Lynn E. Hanover

 

Will do.