The Stovebolt Site Forums The Shop Area Engine Shop recommended timing for towing with 261?

Looking for a timing recommendation for towing a vintage camper that weighs about 2000lbs. with my 49 3/4 ton and stock rebuilt 261. Right now the timing is adjusted by the vacuum method (maximum vacuum minus 1" vacuum) while the octane selector is set at 0. Should I leave it alone or retard the timing with the octane selector? The truck does have a T5 transmission and 3.54 rearend. Dave V

I'd suggest using a delay-flash timing light and setting the total timing to 35-36 degrees at 2500 RPM with the vacuum advance disconnected. Once any towing load at all goes on the engine, the vacuum advance will be virtually nonexistent, and most initial + centrifugal advance settings at cruise speed work best at around 36 degrees. One degree over-advanced robs as much power as a 5 degree timing retard (proved under load on my dyno repeatedly) so an error on the low side of timing advance is better.
Jerry

Does it "ping" under a load? Retard a bit. If not, leave it. Should be fine. Engine was in a lot of working trucks. What it was made to do.

Thanks for the reply. I assume by setting it at 35-36 degrees I am going to need to find TDC and install degree marks on the damper or is there another way? Dave V

"Use a delay-flash timing light". Set the delay dial at 35 degrees and align the ball with the pointer by turning the distributor housing with the engine running at 2500 RPM. It would be a good idea to find true TDC to see if the ball is accurate. Some engines have the ball in the 5 degree advance location. PM me if you want and I'll detail a procedure for finding TDC using a spark plug shell with a piece of round stock welded into it called the "positive stop" method.
Jerry

Jerry will lead you to what you want to know.

Other extraneous information regarding timing marks:

The ball was the timing mark on the flywheel for that particular engine, in a particular year.

You might not have the original flywheel for your engine.

The timing mark/ball could have been TDC, before TDC, or after TDC, depending on year/engine.

Engine was in a lot of working trucks. What it was made to do.

But not with those gears.

Stay out of 5th. gear while towing and don't overdo it on the timing advance. Towing 2K Lbs. won't be a problem. Before the school system trashed about 20 years' worth of dyno test records when they closed the shop I was running, I could have offered a bunch of documentation on what works best for cam specifications and ignition advance curves where low end and midrange performance is concerned. I had a specific test procedure for trailer tow engines in addition to the round track race engines. Gotta get the race car to the track with something!
Jerry

Jerry I did make a positive stop with an old spark plug and nut welded to it with a threaded rod going thru it. Went cw and ccw to locate TDC, scribed a mark there. Measured circumference of damper at 23.1" so 36degrees being 1/10th of 360 is 2.31". Scribed another mark there showing 36degrees. Ran out of time and hope to check the timing tomorrow. Does this sound like a good aproach? Thanks Dave V

You've got the positive stop method down pretty good, but I'd suggest marking the flywheel rather than the damper and using the original pointer above the starter as the reference point. Reach through the hole and put a mark on the flywheel at both stopping points. There's enough room behind the oil pan with the dust cover removed to see the positive stop marks clearly, especially if you use something like "White-Out" for marking the positive stop points. Once both of those places are marked, measure between them and divide the measurement in half. That point is the place to put an accurate TDC mark, Maybe a big center punch dot or a chisel mark, and the bellhousing pointer can still be used to set the timing. Since the flywheel is much larger diameter than the damper, it will also be more accurate.
Jerry

Edit: I'd still prefer a delay flash light to set the total timing at cruise RPM rather than trying to do the geometry to get a 36 degree mark on the flywheel or the damper. I've used damper marks on race engines for setting total timing, but it was always done with a degree wheel during an engine buildup.
Jerry

Jerry Thanks for the excellent advice. It would make more sense to use the large diameter of the flywheel. All I have to work with is a basic timing light. Hope this will work. I'll try this evening and let you know. Thanks again Dave V

I've used Jerry's max advance timing procedure on other engines. One engine in particular would be set to a max of 30 degrees @ 3k rpm. I've also had to back some to 28 degrees if they pinged on acceleration. Every similar sized engine could vary depending upon the wear and engine parts used.
It is a much better way to time an engine than the static or idle settings IMHO.
I often wondered what a Stovebolts max timing setting specs were, thanks Jerry.
Would the 216 & 235 be the same as the 261?

Dave

Dave, the 36 degree figure is a good starting point on a lot of engines. Be aware that the vacuum advance will bump that figure up 7-10 degrees for light throttle fuel economy, but the vacuum goes away almost instantly as soon as even a little load goes on the engine, like passing or pulling hills. Things like cam profile, compression ratio, and combustion chamber shape are big factors in setting the best timing advance, and the operative term is always "don't overdo it!" The centrifugal + initial timing is what we're setting with this procedure, by disconnecting the vacuum during the cruise RPM run.

I really like my delay-flash light, since I can dial in whatever total advance I want and use the 0 mark on the balancer or flywheel as a reference point. I use a Snap-On digital readout light which also has a tach function. Last time I checked, there were several of them available on Ebay Motors for bargain prices.
Jerry

I did check the timing this evening with my method and found it to be about 34-35degrees. This is where it was adjusted yet from the vacuum method. I'm going to leave it there and try it this weekend when we go camping. My wife has better hearing than I do to listen for pinging. I can easily adjust the octane selector if it does. I'll let you know how it goes. Thanks for all the input. Dave V