Pulley & Tune Vacation Day

[partssmann]

Not everybody would understand this but used vacation day to assist Rich Robach do a pulley and tune on friends GT. It is relaxing for me to work on the GT under Rich's teaching. Only PIA was getting to belt tensioner to release pressure to pull belt off power steering pulley. After that job was very straight forward other than the inevitable dropping part or tool and then searching. See pics below. Was impressed how clean intercooler was after 10,000 miles. Wish my Lightning intercooler would stay this clean. Picture of stock and new idler pulley shows how the kit takes up the slack for the smaller blower pulley. Quality machined part. To bad AZ only has 91 octane gas readily available.

 

[BlackICE]

Something to consider. The OEM idler is steel so this isn't an issue.

http://www.engineersedge.com/wwwboard/posts/11510.html

I have a 6061-t651 pulley with inner bore that Im pressing a 6203 bearing into (outer bearing race dia 1.5748"). The pulley is used in a car engine and reaches 250 F during service. There is no thrust load on bearing, only radial.
In the past, Ive used .0005" interference and pressed bearing in (NOT using heat).

Ive had seveal pulleys fail where the bore grows until the bearing is so loose it will fall right out.

So, apparently .0005 isnt enough given the temp range. Im trying to correct this issue, and was running thru calculations based on thermal expansion of aluminum pulley and steel bearing.

From what Ive found, the 6061-t6 has thermal expansion of 13.1 microinch/inch/degree F, while the steel bearing is about 5 microinch/inch/degree F. The bearing thermal expansion is estimate, Im trying to be conservative too. Dont know how to find out true thermal expansion of bearing, perhaps I can call SKF. Anyways, 5 should be about right.

That yields a pulley "relative" thermal expansion of 13.1 - 5 = 8.1 microinch/inch/degree F.

So, if the metal pulley bolted to side of car engine reaches 250 F (which is highly likely), I can expect the bore to grow about .0032 inch. Thats over a thousandth per side. I cant press bearing in with that much pinch...

I must be doing something wrong here, pls advise where Im going wrong. Also, I was thinking of using some sort of loc-tite to help out, but that doesnt do well at 250F either.

The OEM just overmolded the bearing into plastic pulley, so they didnt have to address this issue.

Any help is appreciated!

 

[fjpikul]

Ice I recommend you use Sims' car as a guinea pig.

 

[BlackICE]

Ice I recommend you use Sims' car as a guinea pig.

Neither one of us wants to be a guinea pig. We both discussed making a alloy idler and asked Shadowman what he thought of the idea. He brought up the thermal expansion issues and we dropped the discussion. It may not be a problem, but we didn't want to risk it for a few grams of weight.

Did you know you can save more than 2 lbs if you swap all of your belly pan screws for alloy button heads?

 

[FGT899]

I noticed they have 105 octane at the pump around the corner @ Scottsdale Rd/Lincoln.

 

[Ed Sims]

I recommend we use Dr Frank's car as a test car! LOL

Ed

PS Cool info BlackIce! Thanks

 

[GT Tech]

I doubt the aluminum idler pulley was made for weight savings. It's a lot easier to machine it out of aluminum than steel. Believe me, it's a work of art. Rich and Dennis (GT Guys) did a magnificent job on this piece. I'm just sorry that, due to it's location, nobody will see it. Great job guys.

As for loosing 2 lbs by replacing belly pan screws, (I never weighted them but I can believe it) just have driver and passenger take big dumps before going out. Might work out the same, but a hell of a lot more satisfying.

 

[PeteK]

As for loosing 2 lbs by replacing belly pan screws, (I never weighted them but I can believe it) just have driver and passenger take big dumps before going out. Might work out the same, but a hell of a lot more satisfying.

:rofl

 

[PeteK]

Something to consider. The OEM idler is steel so this isn't an issue.

http://www.engineersedge.com/wwwboard/posts/11510.html

I have a 6061-t651 pulley with inner bore that Im pressing a 6203 bearing into (outer bearing race dia 1.5748"). The pulley is used in a car engine and reaches 250 F during service. There is no thrust load on bearing, only radial.
In the past, Ive used .0005" interference and pressed bearing in (NOT using heat).

Ive had seveal pulleys fail where the bore grows until the bearing is so loose it will fall right out.

So, apparently .0005 isnt enough given the temp range. Im trying to correct this issue, and was running thru calculations based on thermal expansion of aluminum pulley and steel bearing.

From what Ive found, the 6061-t6 has thermal expansion of 13.1 microinch/inch/degree F, while the steel bearing is about 5 microinch/inch/degree F. The bearing thermal expansion is estimate, Im trying to be conservative too. Dont know how to find out true thermal expansion of bearing, perhaps I can call SKF. Anyways, 5 should be about right.

That yields a pulley "relative" thermal expansion of 13.1 - 5 = 8.1 microinch/inch/degree F.

So, if the metal pulley bolted to side of car engine reaches 250 F (which is highly likely), I can expect the bore to grow about .0032 inch. Thats over a thousandth per side. I cant press bearing in with that much pinch...

I must be doing something wrong here, pls advise where Im going wrong. Also, I was thinking of using some sort of loc-tite to help out, but that doesnt do well at 250F either.

The OEM just overmolded the bearing into plastic pulley, so they didnt have to address this issue.

Any help is appreciated!

5 and 13 millionths is what I recall from tables of physical properties. Bearing steel, mild steel, any steel have the same thermal expansion rate. let's say your lowest operating temp on the pulley is 50F, and your highest temp is 200F (remember it's out in the air of the engine compartment, and I really doubt it gets hot enough to boil water). So let's estimate temperature differential is about 150F. So, 150 X 8.1 millionths = 1200 millionths or 1.2 thou. I think you can round it up a bit to 1.5 thou, and you can press fit that, or cold/hot fit it. Then check the bearing function by putting it in the freezer first, to see if it tightens up so tha the bearing is binding. If not, then stick it in boiling water to see it it loosens up too much.
One other idea: A couple days ago I wrote in another thread about a crayon type marker that you wipe on parts to measure temperature. When it reaches a certain temp, it changes color. You use several different "crayons" to bracket the temperature. Measure the temp of your current pulley to see how hot it gets, then re-run the expansion calculations. An IR pyrometer/thermometer should work too, if you can get a shot at the pulley.

 

[FENZO]

Did you know you can save more than 2 lbs if you swap all of your belly pan screws for alloy button heads?

100 belly pan screws = 1lb 10.2 oz. One of us has misplaced a decimal. :biggrin

Ive had seveal pulleys fail where the bore grows until the bearing is so loose it will fall right out.
Any help is appreciated!

As PeteK touched upon.. why not soak the pulley in hot oil and put the bearing in the freezer before assy? That is what we did in the AF with jet engine bearings/races.. sorta the same. Although we weren't dealing with dissimilar metals.

 

[BlackICE]

5 and 13 millionths is what I recall from tables of physical properties. Bearing steel, mild steel, any steel have the same thermal expansion rate. let's say your lowest operating temp on the pulley is 50F, and your highest temp is 200F (remember it's out in the air of the engine compartment, and I really doubt it gets hot enough to boil water). So let's estimate temperature differential is about 150F. So, 150 X 8.1 millionths = 1200 millionths or 1.2 thou. I think you can round it up a bit to 1.5 thou, and you can press fit that, or cold/hot fit it. Then check the bearing function by putting it in the freezer first, to see if it tightens up so tha the bearing is binding. If not, then stick it in boiling water to see it it loosens up too much.
One other idea: A couple days ago I wrote in another thread about a crayon type marker that you wipe on parts to measure temperature. When it reaches a certain temp, it changes color. You use several different "crayons" to bracket the temperature. Measure the temp of your current pulley to see how hot it gets, then re-run the expansion calculations. An IR pyrometer/thermometer should work too, if you can get a shot at the pulley.

Your analysis seems correct. The cold test is easy, but I would use any low temp oven rather than putting a bearing into boiling water. In any case an est 1.5 thou range would require maybe a 2 thou interference fit to make me comfortable. The few driving their cars in the winter, would have a little wider temp range.

 

[PeteK]

Your analysis seems correct. The cold test is easy, but I would use any low temp oven rather than putting a bearing into boiling water. In any case an est 1.5 thou range would require maybe a 2 thou interference fit to make me comfortable. The few driving their cars in the winter, would have a little wider temp range.

I thought of one other thing on the way home tonight--we both made another mistake in the calculations. The expansion rate is 5 or 13 millionths of an inch PER INCH OF DIMENSION. So, if the bearing is 1.57 inch in diameter, 1.2 X 1.57= 1.88 thousandths. Call it 2 thousandths.

As far as putting the bearing in boiling water, sure you could use an oven and cooking thermometer, but the bearings are sealed, so they should not let in any water.

 

[STORMCAT]

Your analysis seems correct. The cold test is easy, but I would use any low temp oven rather than putting a bearing into boiling water. In any case an est 1.5 thou range would require maybe a 2 thou interference fit to make me comfortable. The few driving their cars in the winter, would have a little wider temp range.

ICE, Stop killing your self crunching numbers. I've used this before. : http://www.ellsworth.com/products/a...taining-compound-adhesive-green-50-ml-bottle/

This says up to 300*F. there might be a higher tem range one available. Also if you need more assurance a small set screw would help lock in the bearing. A 6-32 or 4-40 is so small it's not going to affect the balance..

" Benefits of Permabond anaerobic retaining
compounds:
n Single component - No Mix Step Required
n Fast Fixture Speed - Efficient Process
n Ambient Cure - Energy Efficient
n Good Shelf Life - No refrigeration or freezing
needed
n Increases load carrying capacity up to five times
that of the press fit.
Adhesive used: Permabond HL138 "

Upon further review they do make some with a higher temp rating. here is a chart with the specs..
http://www.permabond.com/assets/uploads/files/MKT_US_MRO_081314.pdf

see " Retaining Compounds " chart