Forged TRW piston Question

[tc86gn]

Can anyone give me some input?I have a set of .030 forged TRW's. I get .004 and .0045 piston to bore clearance at the bottom of the piston skirt. I am not a machinist or nothing but I had to take my block and stuff to get the crank turned .010 and new cam bearings and get rods done cause I spun #5rod bearing. The shop calls me back and says that my block has a clearance piston to bore of .007 and .008, as I wanted to see if they would hone a small scuff out of one of the cylinders. That threw up a red flag with me cause I know the guy that did the machine work its just that he is 4 hours away, and these guys are 45 min. away. Anyway to top it off, they also said that the block should be scrapped because the front cam bearing journal was out of round. Holy Cow!!! I was very suspicious so I went to the shop and picked up my stuff and got out of there before they could touch my crank. Funny thing was that they could not answer me when I asked them how they determined the Cam bearing journal was out of round with the bearing still in it!
I checked it. It is out of round by .001. BIG DEAL. I am pretty sure that it is acceptable up to .005. I am just glad I got my stuff out of there. Am I correct? and am I measuring the piston at the right point? Any help would be appreciated. Thanks in advance.

TOM

 

[S2V6RACER]

Did you actually check the piston to bore clearance after you brought it all back home?

 

[tc86gn]

Yes, it was ranging from .004 to .0045 on all 6.

 

[KendallF]

How did you measure the piston to wall clearance? Dial bore gauge? Snap gauges? I presume an outside micrometer for the pistons themselves. I have had trouble with snap gauges showing .001" to .002" smaller than the actual bore size; they say they're good to .001" but not when I use them, apparently.

If you did it the low tech way and stuck a shim in between the piston skirt and the bore, you probably did so at the top of the bore above where the rings stopped; the bore will be largest at the top of the ring travel.

If you really truly have .004-.0045", I'd run it. If your leakdown and oil consumption were normal before, and you did not have piston slap, you can probably get by. I'd have it plateau honed to break the glaze, which should remove no more than .0005" or so.

As far as the cam bearing bore concentricity, I am not sure what's acceptable but did the bearing wear look significant?

 

[tc86gn]

The engine is disassembled. I measured the clearance by using an inside mic and then measuring it with a known good outside micrometer. The same one I measured the pistons with. I measured the pistons at their widest point, at the bottom of the skirt. I measured the bore at approx 3/4 in. from the deck. this motor only has 500 miles put on it ,the only problem was a oil pump cavitational problem in which the pump cover gasket was sucking air. Oil pressure would rise and fall.the problem was corrected. I broke the motor in and the first time I got on it I mean really got on it after 500 miles it spun # 5 rod bearing. I also noticed that the front of the cam had worn the block a little bit,but the cam is fine. I figure this occured during the cavitational problem when the pressure dropped to 0. also, the front cam bearing had not been getting any oil. the front cam bearing was significantly worn too.What they are basicly saying is that the machine shop that set it up, did a bad job. they say it is set up with clearances of .006 to .007 and if they tried to hone out a scuff that there would be nothig left.The out of round cam bearing journal was the biggest sign to me that they either didn't know what they were doing, or they just did not want to do it. The bearing was still in it. How can cam bearing journal wear be determined without removing the bearing? I have never seen an engine scrapped for an out of round cam bearing journal. thats a new one on me. Guess I need to start looking for another block either way. I dont think you can bore a turbo V-6 more than .030.Can you?

Tom

 

[tc86gn]

I really would like some opinions on this stuff. come on guys. Are there any machinists out there?

 

[tc86gn]

Update.
I took my block and stuff to a machine shop that a friend of mine owns in Bryan ,Tx. He checked everything out for me. Crank is saveable needs turned to .010. More importantly the bore on all cylinders is fine. .0035 to.004 piston to bore clearance on all cylinders. His measurements turned out a little tighter than mine did. As for the cam bearing journal being out of round, He said that it was fine and that mine was out of round by .001. This he said was normal.
He also addressed the problem of the cam wearing in to the front of the block. He suggested drilling a .030 hole either in the oil plug or the oil journal for #1 cam bearing journal.
Have any of you guys found a solution for the cam wearing the front of the block?


Tom

 

[Intercooler]

Buy a cam that doesn't have the groove on the #1 cam bearing.

 

[tc86gn]

How will this stop the cam rubbing into the front of the block?