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.

Matt,
Can I assume that the picture which includes the vacuum actuator on the distributor indicates the best location for the hole in the bellhousing? Or, can the hole be located anywhere based on drilling ease/access if TDC on cylinder one is located accurately? Is there a distance from the mounting flange (to catch the flywheel gear accurately) that is available or is it a guess? Is it safe to drill on an installed engine/bellhousing? What are the consequences of losing the cutout disc from drilling (which clumsy/unlucky people {me} will do).

I ask this because timing has been a frustration for me for the 25 years I've owned my coach. Basically I've ignored it in the absence of problems. That has meant that I've been, if you explore the margins, getting lousy mileage, experience a perfectly running engine (?), or flirting with disaster with advanced timing, or some less than optimal blending of the three.

There are limited mods to stock which are universally accepted and generally not up for debate. The Pertronix lobe sensing unit (for my year GMC), blocking the intake exhaust crossover, the flywheel timing for the Onan, and alloy wheels come to mind first. Everyone has their favorites based on their willingness to pay or dig into the innards of their coach. I suspect your "Gunsight Timing" would easily join the list if the bar were lowered just a bit for people like me who see a great idea but are a little intimidated by the process. Perhaps you have a friend out there with a coach "in process" who could do the modification and document it for us rabble?
Doug

Matt:
I have a Dick Paterson distributor coming my way. I wanted to utilize your method for the gun site timing, and this would be a good time to do this while the distributor is out of the way.
=> Good Idea
I have a question. Did you just roll the crank to TDC (0 degrees), mark a tooth, and then count over four teeth for 10 degrees BTDC? I can't work out in my head without looking at the crank which direction Before and After would be on the flywheel.
=> I marked 0, 10 & 20 while the engine was separate from the transmission. I had marked the tops of the teeth and they were hard to see, so I remarked on the flywheel edge.
Are the 0 mark and the 10 degree mark both visible in the mouse hole at the same time?
=> The hole I put in the bell housing (iirc) is 1.125" and only 3 teeth are visible.
I'm thinking of machining an aluminum pointer, which would mount with two 8-32 stainless screws threaded into tapped holes in the trans bell housing. I would make the screw holes slotted, to allow for calibration. This pointer would drop down into the mouse hole as close to the teeth as possible and maintain a safe clearance.
=>That much effort will not get you much, with the just the change from damper to flywheel the resolution is already about 5X better.

When I put the new double roller timing chain in last year, I fabricated a piston stop and carefully worked the crank until I had an accurate TDC mark. The new harmonic balancer mark was off about 1-1/4 degrees. I installed a harmonic balancer timing tape with Zero at the correct place, then timed it as best I could with a timing light. I don't have an advance type light, so your modification would be a welcome feature. My distributor advance weights and pins were stuck, and after getting them loose, I discovered they were badly worn. I expect some improvement with Dick's distributor, provided I can time it accurately.
Thank you.