YODAONE

Obtained TKT-021 Aisin Timing Belt Kit from Rock Auto for 1999 LS400.

This kit contains Aisin water pump, Mitsubishi timing belt, Koyo idler bearing, Koyo tensioner bearing, NTN hydraulic tensioner, water pump gaskets and necessary o-rings to perform timing belt and water pump service.

On information, all OEM supplier components...

I acquired a new precision shoulder bolt from Lexus which is the mating bearing surface the tensioner pulley pivots and is affixed to the oil pump housing...

I inserted the shoulder bolt into tensioner pulley and determined there was excessive side play...

I could discern side movement of the shoulder bolt when fully inserted into the tensioner pulley.

Digital measurements of the shoulder pivot bolt displayed .787-.788."

Digital measurements of the I.D. of the tensioner bearings pivot hole measured .790 - .792."
(the tensioner uses two sleeve bearings inserted from opposite ends, and not one contiguous bearing)

So the best case scensrio is .002" up to .005".

The shoulder bolt tilts in the bearing hole more like .003" tolerance.

With a spinng timing belt and hydraulic tensioner pushing on it, this tolerance seems excessive...

I would expect . 001" maximum

Anyone with comments here?

Also, the Lexus shop manual specifies Loctite Blue threadlock...on this shoulder bolt threads but the dealer tech says not necessary....

The Lexus shop manual also suggests the new shoulder bolt is prelubricated, which it is not...however the (oiled bronze?) sleeve bearings in the tensioner pulley feel slippery, yet are not wet to the touch...

Anyone know firsthand if application of lubricant required. AND what typ Koyo Timing Belt Tensioner Pulley depicting shoulder bolt insertion

"Timing Belt Shaft # 13566-50010 (shoulder bolt)

Banshee365

I usually don't replace that bolt. To your question, a 1 thousandth clearance would be unnecessary in my opinion. I wouldn't be concerned at all with the 3 thousandth clearance. The force applied to the tensioner pulley is pretty much down the middle which doesn't put really any unbalanced load on that bolt. If you want to put a light lubricant on the bolt you can but I don't think the manual specifies anything special. I would probably try a very light film of brake grease as it's very sticky and should stay around instead of just seep out. Also, it looks like they may already be some sort of thread locker on the threads of that bolt. I do use blue loctite when reinstalling. I understand that tech you spoke to doesn't but it sure doesn't hurt for a fastener that's not easily accessed later.

djamps

Try measuring the clearance at full temp?

YODAONE

Here's the thing...If any other critical bearing had .003"play, it would be a candidate for replacement...

While the rotating tensioner bearing itself is excellent Koyo quality, the pivot bearing which the whole assembly affixes is not matched.to the shoulder bolt..and the further from this pivot point, the greater the movement.

I can affordably have selective plating and polishing applied to the shank of the shoulder bolt bearimg surface to reduce tolerance to .0005"

Stay tuned.

Banshee365

Yes, but it's not really a bearing. It's completely unnecessary to machine those parts to a light drag fit as it sounds like you are wanting. The pin may see a very very small amount of movement while running but I'm talking VERY small. My opinion is the parts are in spec. I'll be blunt and honest in saying that I think you are over thinking this one, respectfully.

I have another 1UZ sitting in the garage. I could disassemble the front and remove the tensioner pulley and check clearance on that for you, but I'm sure it's about what you have.

Losiracer2

I have the same RockAuto kit in my 97 for the past 22k miles and I've had zero issues. I think you're freaking out over nothing. Also, why would you see a need to replace that bolt? unless something catastrophic happened to the last tensioner?

YODAONE

1998-2000 LS400 Aisin Timing Belt Kit Instructions Pamphlet Cover Sheet
My approach to maintenance is different from yours and others.

First, lets discuss Aisim Timing Belt Kit TKT-021.

Attached is a copy of the portion of the brochure specifying Lexus model and year applicability, here "LS400 4.0L V8 1998-2000" so I hope you did not use the same kit....

Second, just because I replace hardware with an assembly does not suggest :catastrophic" failure or that I am :freaking out :.

I am however presenting measurements taken of critical engine parts and letting the numbers speak for themselves.

I am not going to reassemble in this fashion.

Quite possibly the shoulder bolt you didn't replace will exhibit even greater tolerances than the nrw shoulder bolt I elected to replace, so what you know now would be different from what you knew then had you taken measurements before reassembling yours...If you have measurements, perhaps you would be willing to share and more fully contribute to the dialogue.

If you have read my posts should inform you that I don't tolerate slipshod work.and correct design defects through meaningful suggestions as I encounter them and share them with all of you good people.

Toyota does many things well, however I will continue to call them out where I think they and, or their suppliers, fell short...and thorough this forum.

Losiracer2

I meant that I purchased a same brand Aisin Timing Belt and Water Pump Kit (TKT030 iirc) off RockAuto, which utilize the same components for the most part. Lexus does not consider this shoulder bolt a wear item as part of the 90k mile service of replacing the TB/WP so I didn't see a need to replace it. This is simply a bolt that secures the tensioner to the block. The tensioner bearing undergoes all the rotational wear over the 90k miles along with the timing belt. To me, you would see more "slop" in the bearing vs. this bolt.

Have you tried what one other member suggested, measuring the bolt OD at operating temperature? the dimension may be designed to be a loose fit when cold but tight within the tensioner housing when at operating temperature.

Or better yet, get a second bolt and measure the OD of that to see if they are similar, then it'll tell you if Lexus manufactured the bolt to the same tolerances. If it is greatly different, then you may have received a defective part and they should be liable to exchange it for you.

YODAONE

Not sure how measuring hot is going to change .003" tolerance...while tge shouldee bolt mah contract an amount, perhaps we can agree so too does the circular bearing...and not contracting...so not sure how engine heat will erase the tolerancr.

I have sent this posting link to my contact at Aisin for comment...Toyota is apparently a stakeholder in Aisin so it is uncertain whether they will respond...yet the bearing assembly is produced by Koyo so perhaps someone will courtesy response.

I do not have information whether the supplier of the shoulder bolt is also Koyo, but it would appear not due to tolerance mismatch.

In the 100's of 000's produced no one has noticed?

djamps

I don't think many people replace the bolt, I didn't after researching online and asking a friend who is a lexus tech. I didn't measure my clearances either, but I do not remember there being any noticable play after 200k miles (2nd belt, original bolt most likely) or I would have done the bolt as well.

Banshee365

Perhaps no one has noticed because the tolerance on that bolt doesn't need to be that tight through the belt tensioner.

To put this into perspective for the viewers who may not have much experience with measurements in the thousandths, a sheet of paper is a hair over .004". The enormous tolerance in question here is smaller than that.

I'm still going to check the other engine I have just for data collection and comparison to what you have.

dicer

You would not want the hole to pin / bolt to be only .001. First off it could seize and even the smallest burr could keep it from fitting together. Secondly I bet those parts do not measure what you say they do. If you used a good micrometer and bore gauge or hole mic then you would be a lot closer in your measurements, it depends on the quality of the calipers you used and how experienced you are at using them, its a feel thing. I see .001 plus errors all the time with top quality digital calipers when measuring ID's especially, they are an okay reference instrument. At work I deal with +- .0002 tolerances a lot. We use air gauges for that and they split .0001 into ten places. Oh and the control on my machine can do the same and with scales it actually does what it says. Its great for interpolating holes with that resolution. Oh and measuring hot makes a huge difference, and since the bolt will be running hotter than the tensioner because it screws into the hot engine and will conduct more heat than the tensioner assembly wagging in the wind from the timing belt, if there was only .0005 per side clearance you could have a seizing problem. In that application a bit of slop is a good thing, also for a bit of freedom to seek alignment to the belt.
Banshee and I once again agree. I would not hesitate using those parts.

djamps

Or as you mentioned, the bolt getting hotter and expanding more than the tensioner assembly during operation.

Banshee365

Don't forget the bolt is steel and the tensioner is aluminum. Different expansion rates.

I also agree with what dicer said on the actual accuracy of the measurements. It takes some pretty expensive and specialty measuring tools to get accurate measurements on the i.d. of the tensioner. I also assumed you used a digital caliper for both.

djamps

I think there's a different bearing material though (copper? steel?) just to throw a monkey wrench into the equation lol