550 timing belt tension

Yes, much debate and "black magic" around this number, or a Churchhill said on Russia: "...is a riddle wrapped in a mystery inside an enigma"...on top of that the usually liability issues that scare off many members from providing the numbers they use.

The usual suspects should provide some input, hopefully someone will disclose an actual number...maybe Wikileaks? hahaha

 

Chuck- No mystery, there are two sets of numbers published, one in the 575M WSM for using one span of the belt, and one in the 612 WSM as the total of two spans. Same as the 550 belts, so take your choice.

Top one is from the 575M WSM. Bottom one is from the 612 WSM. You will need the 575M frequency to add to the short belt span frequency, so can check both at the same time. Cam drives for the 550, 575M and 612 are virtually identical.
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126, you are right on the money.
Sark

 

Where is this tool available from? What is the cost?

 

So why check two places on the belt? One should be sufficient, I would think.

 

One place is very inaccurate and inconsistent.

 

I know this is an old thread but I am confused a bit by this procedure.

First I don't understand when to take the tension reading. I think my confusion comes from the method I used to tension my 308 belts. For that procedure, I rotated the engine to find the spot in the 4 stroke cycle where belt tension was least (where the tensioner bearing pushed away from the body the most) then tightened the bolt. This implies belt tension is not constant, but varies substantially, in the 4-stroke cycle.

The instructions above do not reference a spot in the 4-stroke cycle to measure tension. Is this just assumed to be TDC? Somewhere else? Does it matter? Is the tension uniform throughout the 4-stroke cycle on these modern V-12s? Don't the cam springs impact tension enough to matter when measuring and setting tension?

Second, I don't understand what to do if the tension is not correct. Are they saying just loosen the tension bolt, spin one 4-stroke cycle and remeasure? What if the tension is not correct after that? Change the tension spring? Lever the tension bearing? And again, where in the 4-stroke cycle to measure the tension?

Thanks, and hope my questions make sense.

 

i just rotated crank until it seemed to require more torgue to move than just before to be sure belt section between cams was in tension. Then take readings on both belt lengths and add them up.
Rotate crank twice and do again
If reading too low, apply leverage to tensioner. I had to do that.

 

Thanks for the response. Sounds like a reasonable method but is there any way we can document that is how the frequency is set?

 

I think the way I found the position to check readings is similar to what you described, but I was not looking at tensioner just feel. To check on that, you should set the tensioner, record readings , rotate a little, check again, etc. to see what happens. I cannot recall if I did that

 

So I went back to the 308 method. Tighten when the tension is lowest in the cycle (when the tensioner is most engaged). Then I rotated it at various spots along the cycle and took readings. Turns out the highest readings are in range on the right bank but the left bank needed some help. So maybe this is just a way to confirm the old method is proper? Is the general consensus to take the highest tension readings in the cycle because that is what I did

BTW I believe the belt tension cycle repeats every 120 crank degrees per side. 720 degrees / 6 cylinders.

So unless someone thinks I'm not thinking about this right, I'm torquing down and calling the belt change done.





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so what sums did you get? I recall I set them around 350

 

Never could get a reading on the short belt. Ordered a plug in microphone so maybe thast will help but I think my real problem is my pluck technique. How do you guys pluck that one?

 

took many times to get a reading. I would move the head of the unit near and far to belt and move across the width. Pluck like a guitar string but not too heavy

 

and if you still cannot get a reading, does the sound have a higher frequency to your ear than the long side. you can alos use some apps on iphone to help

 

I was using an app. Could not get it to pick up. Really think it's my plucking technique. Plucked the big one like a guitar sting. Even started to develop a callous like my my left hand guitar fingers. Gotta work on that.

 

Try thumping it with a large screwdriver.

 

I tried that. I thumped it with the handle. You don't mean with the blade do you? I tried small ball peen hammer (ball side) and got some readings from that. Best readings were plucking it like a bass string with my fingers. I ordered a microphone for the iphone. Will see if that helps.

 

Yup, I meant with the blade. Flat or round part, of course.

 

I will give that a try.