Timing tape - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 03-18-2012, 12:54 PM Thread Starter
 
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Timing tape

A follow up question to my previous (recent) post about using a Professional Products "Powerforce" model #80020 harmonic balancer.

The local shop that did the machine work on the engine is advising I use an Engine Pro balancer, but it has no timing marks. So, I started looking for timing tape to fit the 6.8 inch diameter balancer.... to my amazement, I have not been able to locate any. I've tried several Pontiac parts sources as well as Summit, Jegs, etc. and no one has tape for the 6.8 inch balancer. Does anyone know of a source?
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post #2 of 6 (permalink) Old 03-18-2012, 01:42 PM
 
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You don't need a timing tape. Simply do an accurate TDC verificaton to determine the "0" line on the balancer and then use a dial-back timing light for all your timing work. As a short-cut, you can determine/verify the "0" mark with a good TDC verification and then simply measure the circumference of the balancer and divide by 10 to put a line at the 36-degree mark - this is all you'll need to work your timing issues since your timing tab will allow you to see and work within +/- 4 degrees of the 36-degree mark with ease.

The Powerforce 80020 balancer works fine, but it is not SFI-approved. It has 60 degree marks plus a mark at each 90-degree interval. For a street car, there is no issue using this balancer.

The Engine Pro products are serious racing products, but their 2 entry-level quality levels are also not SFI-approved. They do not degree their balancers, because they assume that any knowledgable engine builder will determine TDC and mark the balancer according to where he decides to put the timing pointer - this is a normal part of the engine building process. If you chose to use the Engine Pro balancer, have your engine builder mark the correct "0" point on the balancer and install the timing pointer correctly. Then, use a dial-back light for engine timing, as you should be doing anyway...

I've seen a lot of balancers come apart, including stock balancers, Pioneer, and Engine Pro. One of the key failure modes, regardless of balancer brand, has been the technique used during balancing (drilling and removing material too close to the OD of the outer ring) and bore tolerancing during installation: Many high perfrmance balancers are not slip fit like a stock Pontiac, and the engine builder must hone the bore to the correct press fit size - forcing a high performance balancer onto the crank snout without doing the correct sizing and honing will cause the balancer to fail.

Lars

Last edited by lars; 03-18-2012 at 08:08 PM.
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post #3 of 6 (permalink) Old 03-18-2012, 07:52 PM
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Originally Posted by TommyG67 View Post
A follow up question to my previous (recent) post about using a Professional Products "Powerforce" model #80020 harmonic balancer.

The local shop that did the machine work on the engine is advising I use an Engine Pro balancer, but it has no timing marks. So, I started looking for timing tape to fit the 6.8 inch diameter balancer.... to my amazement, I have not been able to locate any. I've tried several Pontiac parts sources as well as Summit, Jegs, etc. and no one has tape for the 6.8 inch balancer. Does anyone know of a source?
Good move - I've heard some pretty bad things about the Professional Products balancers. Several suppliers have stopped carrying them altogether.

Whichever one you wind up using, make sure you verify that the TDC mark on it is actually TDC on your engine. Sometimes they're off.

I'm running a Pioneer SFI balancer on mine, their part number 872031. It's "almost" 6.80 inches (actually 6.760). Turns out that a timing tape for a little block chevy (6.750 diamaeter balancer) works on it.

Do you have a/c? What year is your car/engine? I ask because if you've got factory a/c and a pre 71 car/engine, and you want to run an SFI balancer, it's going to get difficult. There's only one that I know of that has the beveleed edge on the outer ring that will allow the factory a/c compressor drive pulley to fit over it, and that's the one made by PRW, unit # 2445501. They may not have it listed in their catalog but if you call them, it's available.

If you use some other balancer (like the Pioneer unit I have), then the secret to getting your a/c to fit is to use all 71+ pulleys. Using them means you also have to move all your accessories (alternator, p/s pump, a/c compressor) forward exactly 1/4" to get all the pulleys to line up right.

Bear

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post #4 of 6 (permalink) Old 03-19-2012, 11:06 AM Thread Starter
 
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I do not happen to have a dial-back timing light, so the timing tape is a convenience. Your comment "...Many high perfrmance balancers are not slip fit like a stock Pontiac..." made me wonder what you mean by "slip fit"? That makes me think that the balancer should "slip" on by with moderate hand pressure, as opposed to a light "press fit" that requires the balancer to be drawn in by the bolt. Someone who has built some Pontiac engines told me that the Pontiac balancers do not go on "tight, like a Chevy". I'd appreciate your thoughts on this.
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post #5 of 6 (permalink) Old 03-19-2012, 11:14 AM Thread Starter
 
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I have a '67 factoty air car, although we decided to go with the newer timing cover, water pump & balancer (my cover was in bad shape). Thanks for the "heads up" on the interference with the A/C pulley and the need to relocate the accessories forward 1/4". Hopefully that will not cause any fan/clutch/radiator issues.... I just have a 5000 RPM street engine, so I can't see that I'd need the SFI-approved balancer. Thanks, too for the tip on the SBC timing tape :-) As always, you have good info and it's appreciated.
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post #6 of 6 (permalink) Old 03-19-2012, 01:56 PM
 
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Originally Posted by TommyG67 View Post
I do not happen to have a dial-back timing light, so the timing tape is a convenience. Your comment "...Many high performance balancers are not slip fit like a stock Pontiac..." made me wonder what you mean by "slip fit"? That makes me think that the balancer should "slip" on by with moderate hand pressure, as opposed to a light "press fit" that requires the balancer to be drawn in by the bolt. Someone who has built some Pontiac engines told me that the Pontiac balancers do not go on "tight, like a Chevy". I'd appreciate your thoughts on this.
Even if you don't have a dial-back timing light (put it on your Christmas wish list as your #1 item - you can't tune an engine without one) all you need is a correct "0" mark on the balancer and a 36-degree mark, which you can determine by simply measuring the circumference and dividing by 10. Total timing on a Pontiac (and any other performance American V8 with standard cylinder heads) is nominally 36 degrees, +/- 2 degrees.

Stock Pontiac harmonic balancers are not press fit - they are a snug slip fit on the crank snout, and you can remove them by simply wiggling and pulling them right off (after removing the bolt, of course). You can install one without pulling it in with the bolt (which you should never do with a press fit balancer - you need the right installation tool). A high performance balancer does its job much better if it has a proper press fit on the crank so the harmonic vibrations are well transmitted into the balancer, so many high performance balancers are provided with a slightly undersized hole so they can be custom honed to a specific press fit on the crank snout. Due to the keyway in the hole, a special hone must be used to get the hole to the correct size. A press-fit balancer must be installed with a balancer installation tool, and not pulled on using the crank bolt threads and the balancer bolt: chances are good you'll pull the threads out of the crank.
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