Mallory distributor advance on the 427's

Mallory distributor advance on the 427's

George
George

August 3rd, 2010, 1:04 pm #1

Hi Folks,

I have been troubleshooting a distributor advance issue on my starboard 427 for a couple weeks now. The distributor was originally a Mallory YL 502 BV flat cap. It was rebuilt this past winter at Mallory/Prestolite and the newer advance YH assembly was installed with new springs. It is only advancing about 10 degrees at 3000 rpms. The mechanism seems to move freely and the stop is set similar to the port engine which advances ok and was rebuilt last year by the same shop. The boat had a couple good runs and then one weekend it started hesitating at the 1700 rpm mark and if I pushed it, it would pop back through the carb. (not fuel related, swapped carbs, adjusted valves, fuel pressure 5 psi, new wires, cap and rotor, swapped coil, pertronix ok, no vac leak, pcv ok)
If you look at the Chris Craft 427 data sheet the total advance should be 32-34 degrees.
So, less the initial 10 deg, the distributor should be advancing 22-24 degrees. It should be all in by 3000 rpms. If you look at the Mallory advance curves here, that info correlates to the Chris Craft data.

Here is where it gets confusing, Tim Toth had his distributors done by the same shop awhile back and he was kind enough to send me the curve data sheet from that job.

Tim's advance data does not match up with any of the current Mallory graphs and the 12 degrees total distributor advance doesnt jive with anything except my poorly running engine.

Any thoughts?

Kind regards,
George
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Paul
Paul

August 3rd, 2010, 2:16 pm #2

One of our Forum guys actually runs a distributor repair shop and has given some good data in the past. I will try to look him up, although it's just from memory and no real link I'm thinking of right now.

I actually think it may be Bill Frondorf, at 772-834-6672

He's such a good guy I really don't think he would mind if you called him. You might want to drop Jerry's name too, as he and Jerry have corresponded and maybe even traded boats!

Regards, best,

Paul
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Paul
Paul

August 3rd, 2010, 4:17 pm #3

From the archives........Tim Toth comments
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Paul,

Don`t forget to measure the ohms readings on your old plug wires and new wires and post them here for the Captains needing a wire tune-up . Reset your timing advance with your new dist caps at 10.5 and hang on .

Tim


Paul,

The centerline of the timing dimple on the flywheel is set at 10.0 degrees advance,(aka btdc).No other marks or lines are present,no confusion that way .The dimple has a range from edge to edge of 9.5 degrees to 10.5 degrees .That is set at 500 rpm in gear or dockside at 500 rpm .

Bill is right about total advance also and best checked with a digital advance light.I use white paint to mark the dimple and the pointer ,easier to see with the timing light .

Heading to the boat .

Good Luck
Tim




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From the archives: Bill Frondorth info

total advance
August 31 2007 at 8:43 AM bill (Login billinstuart)
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Everyone sets initial timing, but what you REALLY want is total advance. Is your distributor advancing properly, and how many degrees? Every distributor is different, and throwing hundreds of dollars in parts at it won't cure a defective distributor.


Concentrate on the basics. Is the timing fully advanced at 3000 rpms? Maybe 30-32 degrees total? If you've only got 24 degrees at 3000 rpm cruise, you're losing ALOT of power. Remember those big dogs were designed for 89 octane leaded, so don't go too high on total advance. Current octane is an average of Research and Motor method of octane determination. Carb functioning properly? Flame arrestor clean and of adequate size? Are the props squeeky clean?!?!









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George
George

August 11th, 2010, 1:59 am #4

Ok, here is the scoop. When I called Mallory to get the rebuild data for my distributor, I was told that I have the bronze and white spring just like the "book" says. Well after some digging I found the only advance spring kits with bronze and white springs was the YL advance kit. This is the old advance mechanism with heavy weights. (about 3/8" thick) So I ordered a YH advance spring kit (about 1/8" thick weights)and no bronze or white spring is called out in it. The bronze and white springs are too stiff for the new YH kit. I put in 2 pink springs and the engine now advances like it is supposed to. 24 deg on the distrib + 10 deg initial. As you can see from the above graph, the two pink springs setup has the advance all in by 2000rpms. I might try the two orange springs this weekend and see what happens. I am calling Mallory tomorrow and raise some hell.
Cheers,
George
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Tom Slayton
Tom Slayton

August 11th, 2010, 1:37 pm #5

I am interested in the outcome of this. I would think the advance would be all in at around 3000 but there are others who would think it would be incremental to 4000. Mallory has undergone so many changes of ownership, most of the people there now wouldn't know what a crab cap was. The advance curve on a big block Ford should not be a mystery to them. When you find the right spring combination please post it for everyone, as I am sure there are some others who may need these, including me.

Tom
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Randy
Randy

August 11th, 2010, 3:41 pm #6

Ok, here is the scoop. When I called Mallory to get the rebuild data for my distributor, I was told that I have the bronze and white spring just like the "book" says. Well after some digging I found the only advance spring kits with bronze and white springs was the YL advance kit. This is the old advance mechanism with heavy weights. (about 3/8" thick) So I ordered a YH advance spring kit (about 1/8" thick weights)and no bronze or white spring is called out in it. The bronze and white springs are too stiff for the new YH kit. I put in 2 pink springs and the engine now advances like it is supposed to. 24 deg on the distrib + 10 deg initial. As you can see from the above graph, the two pink springs setup has the advance all in by 2000rpms. I might try the two orange springs this weekend and see what happens. I am calling Mallory tomorrow and raise some hell.
Cheers,
George
George,

34 degrees timing at 2,000 RPM might be a little too much for a marine 427. My concern, at least with my experience on a 38, would be detonation between 2,000 and 2,600 where the engines can be lugging before the boat starts to plane, depending on what props they are turning. Listen closely to the engines for ping/knocking while you are running. Do you have a degree timing light that you can adjust to keep the timing on the 10 degree mark while gradually increasing the engine RPM? That is the best way to document the actual advance curve being produced versus relying on the graphs. Detonation has killed many marine engines. If you are getting detonation under a load, you can retard the timing by rotating the distributor while under a load until it stops then check where the timing is with the timing light. This is generally a two person job, one to drive and one to document the best timing curve. You will know where not to go on the advance curve and can select springs accordingly. Remember, rotating the distributor will change your base timing.

Keep us posted on you progress.

Randy
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George
George

August 11th, 2010, 8:38 pm #7

Randy,
Thanks for the advice.
I do not plan on leaving the 2 pink springs in. I put those in to see if the mechanism was even functioning and to prove the stop was set correctly. The plan now is to put the 2 orange springs in. If you look at that curve above in this thread, that advance is all in at about 2800. I do have a digital tiiming light to check the advance curve in real life and I plan to do that this weekend as well. I will keep you all posted.
Cheers
Geo.
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Randy
Randy

August 11th, 2010, 10:25 pm #8

No problem, I am enjoying hearing what others are doing with their CC projects. I forgot to mention that I agree, all in at 34 degrees at 2,800 - 3,000 RPM should be fine. A stock 427 should be peaked on torque and the boat should be planed out by then. Most of them will never see 4,000 RPM, so curving for that would probably not be the best. Bottom line, just make sure it does not detonate (ping) at any time on the way to 3,000 RPM.

Randy
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Paul
Paul

August 19th, 2010, 8:37 pm #9




regards,

Paul
Last edited by FEfinaticP on August 20th, 2010, 7:08 pm, edited 1 time in total.
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George
George

August 20th, 2010, 6:47 pm #10

Thanks for posting that bulletin again Paul. I noticed here on page 2 of that bulletin, in the 427 numbers, maybe a misprint? If you look at the difference in deg advance between 700 and 1000 dist. rpms, (that equates to 6.6-7.8 or 1.2 deg advance for crank rpms increase of 600rpms. If you look at the other engines and the mallory plots earlier in this thread, they seem more normal. It looks like there should be around 12-15 deg at 2000 rpms not 7.8 deg. Maybe the 3.9 should be 6.9 deg?
I created a nice spread sheet and will post it when I get it populated. Now that I am up and running, I don't mind experimenting with the springs and seeing what the different strength springs will do. We know what the stiff YL springs don't do- let the engine advance properly.
Regards,
George
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