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I posted a previous thread questioning tolerances between the Timing Belt Tensioner Pulley/Bearing and the pivot mounting shoulder bolt...
Now I am looking at the Timing Belt Idler Pulley and its mounting bolt under the same lense..
My finding is the fit between the semi-shoulder bolt is imprecise...about .003"-004" of play between the shoulder and the bearing mounting hole...
This suggests that when the idler pulley is torqued down it cannot center...and there is no centering provision on the aluminum oil pump housing resulting in unecessary camming....and I am unpersuaded by earlier remarks on the Timing Belt Tensioner bearing that engine heat could eliminate such a tolerance gap.
Notice the gap between the bolt and the bore just to the left of the shadow line (just below the chamfer) ....and the gap just to left of shadow line after shifting the bolt. New Timing Belt Idler Pulley Bearing Bolt..the should shank should be longer and precision machined... The bolt moves side-to-side when the shoulder bolt is pressed flush to the Timing Belt Idler Pulley Bearing mounting hole recess. Found this image online of oil pump...In relation to its mounting orientation on the engine it is shown upside down, but the Timing Belt Idler Pulley Bearing mounting bolt screws into the boss with tapped hole at lower left (no centering provision)...You must use a torque wrench to factory specs....thread lock? Stock photo of front of engine showing orientation of timing belt components...tensioner at left and idler pulley bearing at right . NOTE: This is an LS430 engine.
For function, I realize the bolt does not have to be centered....but because it fastens to an Aluminum casting cannot be tightened much.. seems to me that the pulley could shift somewhat in the shoulder bolt to Idler Pulley Bearing mounting hole...It doesn't cost any more to more closely tolerance the bolt.....in fact I have commented on other posts in this forum about hardware fit.
Why do you say that it would not cost any more to more closely tolerance the bolt? Tighter tolerances mean less room for error in manufacturing and thus more expensive tooling and more time to be spent manufacturing the part.
In the event that friction between the pulley and oil pump mating surfaces doesn't prevent the pulley from shifting in the amount of the 0.004" that you estimated, there would be no chance of camming because the net force being applied to the bearing is in only one direction.
The reason the shank of the bolt is not longer is because the rear surface of the pulley and the front surface of the oil pump housing are meant to make firm contact, a longer shank would potentially prevent that.
I cant understand what makes you think there is a problem here. You could potentially dissect every component of this vehicle and claim that it does not fit together as well as it could.
Why do you say that it would not cost any more to more closely tolerance the bolt? Tighter tolerances mean less room for error in manufacturing and thus more expensive tooling and more time to be spent manufacturing the part.
In the event that friction between the pulley and oil pump mating surfaces doesn't prevent the pulley from shifting in the amount of the 0.004" that you estimated, there would be no chance of camming because the net force being applied to the bearing is in only one direction.
The reason the shank of the bolt is not longer is because the rear surface of the pulley and the front surface of the oil pump housing are meant to make firm contact, a longer shank would potentially prevent that.
I cant understand what makes you think there is a problem here. You could potentially dissect every component of this vehicle and claim that it does not fit together as well as it could.
Several of my posts go to hardware fitment issues..feel free to explore them.
I repped a wide range of fasteners, machined parts and fasteners; mil spec. My family had a plating business and I learned a great deal, .so perhaps I notice things through the lense of experience...
As for Toyota, their body hardware is better than most...generous plating but in several instances it merits improvement...(you can still remove their converter flange bolts after 20 years without torching)
I have a friend who tells me;"If the chicks don't notice it, I don't fix it"...
He has his point of view and of course I have mine...
Tighter tolerance parts perform better and contribute to overall durability and function ...be it engine, drivetrain brakes, HVAC, steering, suspension, electrical or chassis.
A non machinist doesn't understand what is required to hold ultra close tolerances, and the amount of scrap and cost from having those tolerances.
We loose $20,000 dollar parts all the time because of .001. Unnecessary default CAD tolerances cost big money as well not only the fighting the tolerance at the machine but also once it hits the quality control room, and the cost of nonconforming material paper work etc.
(So my post covers the down side of a more precise fit)
If this were a part housed within the engine, I would assume a super tight tolerance of .0001 would be needed, but as simple as a bolt affixing an idler bearing to the block, the ***** in the bearing would self-center and not tweak the alignment or cause the belt to move off center. When the bearing rotates about the inner race, the ***** would center within the groove and the outer race would be independent of the clearance between the bolt shoulder and the inner race (see below). As it sits, no direct tension is being applied to this idler against the belt, it is just there to act as a guide for the belt.
If you're still worried about this tolerance, can't you have a machine shop press a very thin sleeve over the shoulder of this bolt I'm sure a company makes them?
02-04-17, 08:55 PM
Timing belt idler pulley fastener tolerances
