Right but I was more just referring to the most of the mass of metal, which is the tensioner housing itself.

 

So before posting I had a professional fabrication shop and machinist take measurements....

This is the same shop that resolved the brake pedal and gas pedal pivot mechanism slop...
check out both postings on this forum...

Before digital measurements were taken I had already determined by wiggling the bolt in the bore that there was excessive play.

I have another vendor with a "bearing heater"...
This device is used to thermally expand bearings to ease insertion over long shafts and to improve fit.....about 300 - 500 F.

I am informed that 200-300 F will.not correct the tolerance between these two components.

These are mass produced components , by two different manufacturers so understandably the fit is not optimized, but easy to resolve.

I see excessive movement between these components which may cause the tensioner pully to exert uneven pressure over width of timing belt.

Possibly it increases timing belt (slap) noise or sporadically transmits metallic noise between shoulder bolt and bearing components discernible by the knock sensors at various times...??

I will take measurements of the old components and report my findings..

 

Okay I didn't double check the number I found with a quick search. The coefficient of expansion for steel listed as .000006 in/ per deg F.
And I can say that this is what I have seen in actual conditions. So if you check your part at 0 deg F and then at 300 deg F that is .0018 difference, which is very close to
.002 so having the bolt smaller by .003 in diameter is a good max diameter dimension for the bolt. The aluminum part is going to run much cooler than the bolt will, it is independent from engine heat and has air flow from the belt to keep it cool.
Oh and checking the dimension at a more standard temp to 300 looks like around .0014 .
In the end it doesn't matter who makes the parts, they work off a drawing that will note the tolerances that the OEM denotes.
And even the axial location of the hole in the bracket has a tolerance as well, like I said before it is best to have the slop, the pulley will self align with it. If you tighten up the clearance too much you maybe clamping a misalignment in the unit and cause it to distort the alignment of the pulley on the belt, your trying to fix something that Lexus likely did for a reason. If you can get all the axis's and clearance perfect then all would be good, I wouldn't want to spend the time fooling with it. How many belts have gone bad because of that hole having some wiggle?

 

If this would've been a noticeable problem over the almost 20 years the car has been on the road, I'm sure Toyota would've release a TSB/Recall for the affected parts. They're typically one of the most safety conscious auto manufacturers out there.

 

Alright, I usually try to be the first to admit that I'm wrong. Although I'm not saying my opinion of how tight this tolerance has to be is that far off base, but your tolerance could indeed be bigger than intended. I spent a couple minutes getting the timing belt tensioner assembly off a bad engine that I have in the garage that I've yet to do an autopsy on. The timing belt was done by a dealer per the Lexus Drivers website recently. The timing marks haven't worn off yet. I'm assuming the tensioner and idler were replaced per dealer policy.

Here is the meat and potatoes: My bolt mics at around 0.7877". The ID of the tensioner measures around 0.7895". That makes the clearance on this one about 0.0018" or 1.8 thousandths. That's nearly half what you're measuring. And judging by what you've said, you're clearance could be even larger than that. I cleaned any lube off the bolt and front the inside of the bore. The parts fit together fairly tight with a very very small amount of play. With a light film of grease on the bolt there would be no play at all, and there really wasn't before I cleaned it. I also confirmed that the hydraulic tensioner piston pushed directly in-line with the center of the bearing pulley. With that fact, I still keep my stance that this clearance doesn't have to be insanely tight like 1-thousandth or less. You could have it sieze at that point I think.

The bearing say's NSK on the dust covers. I'm assuming it's a dealer part.

If I were you, and I had noticed this, I would mic the bolt and compare it to what mine measures. That will tell you which part could be slightly off. I'll bet the bolt is good. At that point I would consider having Aisin or Rockauto replace the part rather than trying to do some custom machine work to the bolt. It's already pretty good.

Disclaimer: I do not have an inner bore gauge, especially this small, to really 100% accurately measure the i.d. To obtain this measurement I set the i.d. side of an analog caliper that I have in the bore, locked it, and rechecked for as tight of a fit as I could and proceeded to just mic the caliper with a very good analog mic that I have. I'm confident in my bolt measurement within a few tenths but the my i.d. measurement could possibly be a hair under what it really is. Although I think it's VERY close.