Half-Breed

[Zachalanche]

After many weeks of chasing my tail on a number of things This engine is finally going back in.



The pilot bearing I ordered turned out to be .001" too small. when I went to install it, it went all the way in with one tap of the hammer. I was able to slide it back out with my finger. So I measured (with perfect inaccuracy) the OD of the pilot bearing at 1.094". Based on this i made the assumption that the pilot bore in the crank shaft was too large (I have heard of this happening on some stroker cranks in the past so it seemed like a reasonable possibility). I contacted LSXcelleration who contacted Molnar, and after a week or 2 they told me that I needed to have a custom pilot bushing made. So, I contacted Molnar directly. They measured some of the crankshafts they had in stock and confirmed there was a dimensional issue, and that they would send out a custom pilot bushing. After not seeing anything in the mail for a couple weeks, I called Molnar again to see if the had sent the bushing. Well, it turns out that they aren't any better at measuring than i am. Prior to machining some custom bushings they went to their local napa and measured a pilot bearing and found it to be about .001" larger than the crank bore, so now they are telling me the crank should be correct. This was very confusing to me. So, I re measured my pilot bearing - this time I get 1.093 - crap, either my calipers are not that accurate, or they were dirty the last time i used them. Then I went to Napa and picked up a pilot bearing and it measured .001" larger than the one I had, and of course it installed just as it should. So there you have it. A simple problem caused by a simple part that I managed to turn into a (almost) month long disaster. But, in the end I am happy the crankshaft is correct.

Once that Hurdle was cleared my next task was to correctly shim my throw out bearing to have the correct air gap with the new clutch. not a challenging task....except...at this point I was still operating under the assumption that I had done this wrong previously and it cost me an engine. the first thing I did was re-install the old clutch to see if I could confirm that the 5 shims i had originally installed was incorrect. It was very difficult to get a good measurement from the back of bell housing to the clutch fingers because there was massive differences in the height of each finger. As a result, I could not confirm that the old clutch had the proper air gap between the clutch and throw out bearing, but I did confirm that the air gap was not negative (meaning the throw out bearing would always be pressing the clutch even when fully collapsed / disengaged). As this was not an obvious smoking gun, this left me scratching my head. So, i moved on with the installation of the new clutch. I got good repeatable measurements from the Bell housing to clutch, but when I measured from the throw out bearing to the transmission face, I would see up to .050" of variation depending on where i measured on the transmission face. I had a length conversation with American Powertrain about this. The told me that most people just take a measurement in one spot and move on, so they don't really know if this issue is common. additionally, they haven't ever had any cases where the transmission face hasn't been flat. Also based on the range of measurements I was working with, we determined that i needed to run 6 shims with the new clutch, and the air gap would be in spec regardless of whether I used the smaller or larger measurements (for throw out bearing to trans face). I'm 1 shim short here so they sent me a bag of shims free of charge. At this point I'm accepting that my measurement methods, or my calipers are creating this error, and the transmission is likely fine. Besides, I have not had any shifting or vibration issues with the prior use, so I'm not expecting large dimensional errors to be valid.

A few days later the shims show up, I put 6 shims behind the throw out bearing, do one final set of measurements just to double check, and I drop the engine in. Now, not having an obvious smoking gun related to my thrust bearing failure, I'm extra paranoid about this engine install, so, I decide to check the crank end play with the engine in the car. this was not an exercise to obtain accurate crank end play, I just wanted to make sure there was some as it would be validation that nothing is pushing on the crank that would inevitably lead to another thrust bearing failure.......Um....there's no end play...*****. What if I can hold a small mirror in the stater pocket and see if throw-out bearing is pushing on the clutch?...o crap I just dropped the mirror into the bell housing.



And out we go with the engine again. OK, now I'm measuring everything related to the back of the crankshaft and the input shaft on the transmission. and in every possible case where there could be contact, there is more than enough clearance available between the end of the input shaft ant the bottom of the pilot bearing bore, or the end of the splines, and the back of the pilot bearing, etc.

I Grab my old crankshaft and start taking measurements. and as I go to measure the total depth of the pilot bearing bore, I see this:

that's not just some grease in the bottom of that hole. there is clear evidence that there has been some metal-on-metal contact (oh and I think the pilot bearing is in backwards...lets not worry about that now). Sure enough, the depth measurement here is over a half inch less than my new crankshaft. the new crank is drilled all the way through and uses a plug. the old crank has a much shallower hole. Even more interesting is that the amount of overlap between the pilot bore depth and the input shaft length was close to .040" which is close to the amount of additional crank end play that i measured before i disassembled the old engine. This is the "smoking gun" i have been looking for. everything makes so much sense now......including the slow cranking issue I could never seem to solve.

Back in the car the engine goes. and the crank end play is....still 0....um....maybe if i pump the clutch a couple times, just in case the disks aren't perfectly aligned are creating some bind on the input shaft...oh here we go. .005" of crank end play with the engine in the car. Finally, things are starting to come together.

Now I am just waiting on mufflers to show up, and I can fire this fresh engine up. If i was 20 years younger I would already be driving it. But I'm older, more patient, more responsible, and more lamer now.

[chunger]

If i was 20 years younger I would already be driving it. But I'm older, more patient, more responsible, and more lamer now.

Lordy, ain't this the truth!

[Zachalanche]

Just a couple pics from the Valley of Fire Cruise at LS Fest West 2025