pcm 351 timing

bigkitch · Outlaw Joined: 16 Jan 2006 Posts: 161 City: Oakville

hey guys and gals, jsut wondering

my 85 supra has the ford/pcm 351 and the timing is real messed.

heres the scenario....in order to get the boat to run right, i have to stack up the degree of timing. when it was in for service the tech said he adjusted to 10* which is normal for ford small blocks...but the thing ran liek a piece and bogged liked hell

i have heard the timing sets on these....that for the gears they have cheap teeth and can break and casue the chain to slip throwing the timing way out...

anyone heard of this? i still have to take of the front acces to see whats goin on...but jsut wonderin if anyone with an older boat has heard/seen this

Commodore · Ladies Man Joined: 20 Jun 2005 Posts: 11636

bigkitch if you had a broken tooth on your timing chain you would know it. Your timing would be way off, and you would hear a lovely grinding noise in the timing cover. Best way is to pull of the timing chain cover and see.

But those 351's are very sensitive. It doesn't take much to get them off. I run two 351's in various applications. One is the boat. You know the talk, so it sounds like you know somewhat what you are doing. Work the distributor cap a bit. Having the cap slightly off will make a mess.

Have you checked your wires and plugs first?
Cap has all good connections? Points still good? (those are notorious for causing firing problems)

Like I said, I've had two. One is now 18 yrs old, and I have owned it the whole time and never had a timing chain problem. I would check your cap first.

Fast351 · Outlaw Joined: 08 Sep 2003 Posts: 133 City: Dayton, MN

The other thing to check is the advance mechanism. Depending on the vintage, you'll have either mechanical only or vacuum and mechanical.

10* timing should be set with the vacuum advance disconnected and at idle.

Then connect the vacuum and rev the engine up while checking the timing. Under full load, you should have about 30-34 degrees at 3500RPM and up, and under light load (if you have vac advance) it'll be in the 40+ range.

One common thing that happens is the mechanical advance plate will rust and start to stick. Just pull the cap and rotor, and see if the weights and plates move freely.

Also check for vacuum leaks. Vacuum leaks the engine will run fine above 2000-2500 RPM, but run like a turd, if at all, below it.

bigkitch · Outlaw Joined: 16 Jan 2006 Posts: 161 City: Oakville

alright, sounds good.

Yah, with the timing gears, it was jsut somethin i had heard in past years, didnt seem liek a reasonable answer, but jsut thought id hear a second opinion.

It sucks cause the guy who had it before me tinkered and put in mustang 351 aftermarket parts, such as msd billet distributor, conversion to electric fuel pump, whicch i had to put a holley regulator on. thing ran lke 5-10 psi...dummbas

but all the plugs, wires, coil are new, already went though the basic route and the distrib seems to be in ok shape but i havent pulled ito ff for a bench test

Fast351, factory original 351 supras, form what i know, did not run vacuum advance distribs. the problem is the msd on the boat has a vacuum and mechanical advance, so im contemplating in that it has somethin to do with the fact that the vacuum isnt hooked to anything, which is the way i bought it

Hollywood · Posted: Jan 02, 2008 7:29 am Post subject:

You should not be running vacuum advance in a ski boat application. Get the right parts for your engine.

To check your timing chain, take off the dist. cap and crank the engine by hand. If there is any lag between turning the engine and the rotor spinning you have a timing chain problem (stretched chain, worn teeth) but like haugy said if there were real problems you'd already know.