TDC Necessary for T-Belt Check?

[OK-944]

I've had great luck using the twist method for belt adjustments...but I cannot see why others recommend setting the engine to TDC prior to checking/adjusting belt tension.

I do understand that there may be some risk...that while adjusting tension a belt might slip a tooth or two - then again I can always create a fresh reference mark from belt to cam with a marker.

At any rate...what's the big deal with needing to set to TDC prior to checking belt tension?

[9FF]

...At any rate...what's the big deal with needing to set to TDC prior to checking belt tension?

It can be in any position to check it and even to adjust it. Thing is you normally do these things as part of a belt change and you need the engine at TDC for that.

[pfarah]

So I take it that TDC is not required to check/adjust belt tension. I did read somewhere that the car should sit overnight prior to belt test; is that correct?

[944tothefloor]

Originally Posted by pfarah

So I take it that TDC is not required to check/adjust belt tension. I did read somewhere that the car should sit overnight prior to belt test; is that correct?

About it sitting overnight, why is that? Tensioning closer to operating temperature seems more practical.

And that is correct; tdc not required while checking/tensioning because the belt stays on and maintains the alignment.

[rhett]

^^ Tensioning while the engine is cold is the recommended way. The Porsche block is aluminium and that expands quite a bit when warm, this could lead to an inaccurate tension if set at this point, as when the engine cools, the belt could possibly end up being too slack.

[alan6272]

I put mine at TDC when I changed it witch of course is the only way. But for re-tension? I am not sure with our motors but when I change TB's on other motors the cam shafts sometimes have a rebound affect just from the spring action from the valves, in other words the cams can turn a little if not on TDC which could cause the tight side of the belt to have more play making it harder to tension the belt. If it's recommended to be on TDC then thats how I would do it.

[pfarah]

Thanks Rhett for confirming what I've heard. I'm saving my pennies for the Arnnworx tension tool.

[tamathumper]

Seems safest to put both the crank and the camshafts at a known relative position before messing with the only component that keeps them synchronized, and the easiest position to determine for both is firing TDC on cylinder 1. Someone recently posted their timing belt lost a bunch of teeth, and I wouldn't want that to happen while I was mucking around with the belt.

[mattdavis11]

You are going to roll the motor around anyway, why not set it to TDC. You don't need a flywheel lock to re-tension. Don't tension the belt with a warm motor, ambient only.

[djnolan]

I am getting a whine from the WP when warm, so I think I tensioned the TB too tight. What did I do wrong, and no I didn't use any type of tension gauge? (this is a car w/o the spring tensioner)

[mattdavis11]

Back off the tension on the balance belt. I like my BB to whine a little. John AZ says the right tension on the TB is where you can spin the pulley on the water pump by hand with a little effort. I twist then spin. Deflection is about 90 for the TB, a tad more for the BB.

[djnolan]

Matt,
Do you mean spin the pump while twisting the TB 90 degrees?

[mattdavis11]

Guess I should have been more clear. I'll twist it first, then spin the pump to check if my twist was correct. It's about the feel and I second guess myself every time if I have the same feel as I did the time before. My ears tell me everything about the balance belt.

In my experiences, a loose balance belt can cause problems, and that was after a calibrated P9201 tensioning tool was used. Brand new belt, tensioned to 3.5 then 2.7 after 1500 miles, it lost all but 9 teeth on one side. No more P9201 for me, if it whines, it's good.

[John_AZ]

+1^

The balance belt will feel sloppy.
Make sure you keep it below the WP waterpump pulley by turning the BB tension roller CW-clockwise!

I am not sure of which car you are working on.



or information on the WP waterpump pulley test.



If your car has the "mechanical spring tensioner" WSM tension UPDATE.



Each of these methods require experience.

Recheck the cam belt after 800 to 1000 miles. A new belt will settle in the pulley teeth and get loose.

GL
J_AZ

[djnolan]

In this case it is an 85.5 car.

Has anyone used a mechanics stethescope to listen to the rollers? For instance tightening the belt so the adjustor roller (timing or balance) is just before the point of shrieking when the motor is revved to about 2500?

I tried it and am happy with the way the TB came out, but the BB frapps a little when cold.

[John_AZ]

Originally Posted by djnolan

In this case it is an 85.5 car.

Has anyone used a mechanics stethescope to listen to the rollers? For instance tightening the belt so the adjustor roller (timing or balance) is just before the point of shrieking when the motor is revved to about 2500?

I tried it and am happy with the way the TB came out, but the BB frapps a little when cold.

hmmmm.

"point of shrieking" method using a stethoscope.

My problem would be the uncontrolled fear of my hand shaking so badly that the probe of the mechanics stethescope would move into the running engine belts and rollers and destroy my face when ripped from my ears.



I would not be willing to suggest this to anyone.

J_AZ

[djnolan]

John,
I note your safety concerns and would defer to professionals in that area.

I just needed to touch the adjustor pulley stud for a few seconds with the stethescope, and have the other hand on the throttle. You don't hear the same noises at idle that you do at 2500 revs.

Is this really unsafe?

[John_AZ]

"Is this really unsafe?"

Correct, I am not a professional certified factory Safety specialist.

I picture myself under the front of the car, front wheels on ramps or jack stands.
My head 18 inches from spinning belts, rollers, pulleys along with a touch of hot engine oil or coolant.

If you read the cam belt installation instructions, The engine should be cold when installing the cam belt. 68 degrees if I remember??

How can you get an accurate cam belt adjustment with the engine running---even for a few minutes ---as you listen to the rollers with your stethoscope?

Do you use a wrench on the running engine to adjust the tension as you listen to the sound of the rollers with the stethoscope?

J_AZ

[djnolan]

I guess we have a slight misunderstanding...

I first tensioned the belts cold and then tightened everything up and then started it up and listened with the stethoscope. I checked with the stethoscope from above and not from below and only when the belts were tight and I was not doing anything else except reving the engine.

[John_AZ]

Actually, I had an idea of what you are doing and it sounded interesting.

You can tension the belts with any method you choose.

Clarks advises the belt tensioners and rollers be removed and spun occasionally to check for noise and wear.
Porsche suggests changing the tensioners and rollers every 60K miles +-
(Clarks and others says "every other belt change" but many do not keep accurate records.}

Porsche TSB does allow a little noise on the cam belt idler roller as "normal"

If the tensioners and rollers are in OEM condition, without any wear, your method may work if done safely.

The WP water pump pulley and the tension on the cam belt must be appropriate to allow for the very small expansion of the engine when at normal operating temps and not be so tight that it will destroy the WP seal and bearing.

If the stethoscope cam belt or BB roller adjustment can do this, you have a good idea.

J_AZ