Home » Public Forums » GMCnet » New and more accessible timing marks (A drag over from dyno - land)
| New and more accessible timing marks [message #364504] |
Fri, 04 June 2021 17:42  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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When I was checking the timing I one day I thought to myself, “If every time of the thousands (no joke) that I have checked ignition timing on an engine it was as hard as this, I would have found a better way.” Well, when I start thinking about things, this can be dangerous. I didn’t have to look very far. All I had to do was remember that most all the test engines I have had responsibility for over decades of career time in the test laboratories had the timing marks on the flywheel.
Email guys, this is also posted on the photo site as a *.pdf ready for printing.
Gunsight timing By Matthew Colie 04 June 2021
New timing marks for Oldsmobile in GMC.
Anybody that has tried to check, or worse yet, set the timing in any GMC will see the value in this mod in just the next paragraph. It is also interesting to mention that my engine now has a scale such that even a single degree of the actual timing is very obvious.
My engine has a second set of timing marks that are visible through a hole in the bell housing. This is easier to see and way easier to get to than those on the damper. There is also a reference mark in the edge of the rear for the block. It takes very little effort to do this mod when the engine is out, but I am sure it could be done with the engine and transmission in place..
The picture posted here, (sorry e mail guys I will post the document with the pictures site later) is indeed what you actually get to see. For those that have not set timing, I have also included a picture (the best I could do) of the OE marks. This was the best view I cold get with my camera and those that have done this will admit that this is about as good as it gets.
Discussion of my mod for those that care.
Talk about convenience, it is also just about next to the distributor, so if adjustment is desired it is convenient to do. I also put an adapter in the cigar lighter (here after referred to as the DC mousehole) to get me the DC for the timing light. This works, but it is less than ideal because the engine hatch is in the way. I did have a plan to add a power point that is more convenient, but that still has not happened.
Using a holesaw to make the window in the bell housing is simple. The hardest part is getting the crank to 0° to make the marks. When my engine was on the work stand, this was real easy. So, I made a bunch and made the reference on the back of the block casting as well. Unfortunately, that first set missed. I had marked the top of the teeth and this was not very visible in the final assembly. I just made new marks both paint and engraved on the rear face of the teeth.
In Figure 2, the reference mark is hidden by the vacuum pot.
The real big gain here is the resolution here. There are 144 teeth on the ring gear. So, that is 2.5° per tooth. Between 2 teeth is 1.25° That is just a whole lot bigger and clearer than peering down though the belts and hoses at 1/4 inch = 4°. The next huge gain is the fact that I was now next to the distributor and could watch the mark move when I moved it and check that it stayed there.
The development story:
When I was checking the timing I one day I thought to myself, “If every time of the thousands (no joke) that I have checked ignition timing on an engine it was as hard as this, I would have found a better way.” Well, when I start thinking about things, this can be dangerous. I didn’t have to look very far. All I had to do was remember that most all the test engines I have had responsibility for over decades of career time in the test laboratories had the timing marks on the flywheel.
First, there is an important difference with both the majority of test engines and those installed in over the road vehicles. That difference is Flywheels with degree markings engraved. Even the durability engines on waterbrakes still have them, and if they have a bell housing at all, it has a window with a pointer. So, this is not an original idea that I can take credit for, it is just a technology transfer that took way too long.
For those that might attempt this, it is way easier to move the crank when the spark plugs are removed. The hole in the bell housing does not break the flange at the margin. I drilled that with the transmission bolted up and was able to capture the loose piece, but the engine was still out of the coach. The hole is 1-1/8 because that is a good size to have for running pipe.
I first marked the teeth on the top but as soon as I bolted on the transmission, that mistake was obvious. And when in the coach it was a bigger problem. That is when I went to the red paint. This is the view you might have if you cut a big hole in the lift of the top step.
Two interesting notes: Figure 2 was taken using the timing light flash as light.
The syringe is in that picture because I lost my golf tee. There are two sets of clips on the power lead because I was trying out an HF adjustable timing light. No report on that today.
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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