Dennis Moore

KC Baja,
I would say that it would be more unusual if you purchased the parts from Mercruiser than if you purchased the parts somewhere else! I am pretty sure that the only people that install the expensive Mercruiser engine parts are the ones that are getting them paid for by Mercruiser warranty. Buy the cam, lifters and timing chain/sprockets from Edelbrock and don't look back.
I am a Mercruiser Master Technician and for the last thirty years the only time I ever installed Mercruiser ENGINE parts was under warranty.
The exact same parts can be purchased much cheaper locally!
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Griff

Ditto on getting the aftermarket stuff. Its going to be apart anyway, so you may as well add a little HP for less $$$ than the stock Merc stuff.

As far as the cam/dist gears wearing out in 400hrs. Could have been caused by poor lubrication by the prior owner.
I would guess that the lobes of the cam wore down and the cam was "walking" in the block. The lobes of a cam are slightly angled so that the pressure form the lifters forces the cam toward the rear of the engine. If the lobes wear down, the cam will start to walk.
When I tore my 454mag with 400hrs down, I found out that my cam was probably walking slightly. The cam/dist gears had some wear and the bushing on the bottom of the distributor was an oval.
Good luck !!! (haven't I said this to you before )

blown formula

In regard to the distributor gears, a tech from Merc performance in Wi. said GM had some bad runs of distributor gears that would wear to points like razor blades & or wear teeth completly out. Mine did the latter on a '97 454EFI-Mag. The cam was fine, replaced the gear, flushed the engine and every thing was fine. It seems GM used too soft of iron in the gears.

Holy Smokes

That's interesting. Mine is a '92, not sure how many years the "bad gears" were a factor. We'll find out if the cam gear is indeed worn as bad as the distributor gear. They have already replace the distr. gear and had the same issue. Therefore, it should be down to either the cam gear or the timing chain/sproket.
My wondering mind asks the question.... if this was a problem from GM, was there ever a recall that fixed this problem?

500hps

I HAVE A SET OF HP 500 CAMS THAT ARE USED AND IN GREAT SHAPE . THE ENGINES HAD 100 HOURS AND I WILL SELL CHEAP SINCE I AM UPGRADING GOOD LUCK TOM 610 935 8810

JaayTeee

did anybody check the" dentonation"
a.k.a. "knock" sensor ?,
this could be sending a false "knock" signal,
to ECM, then module, causing timing to be retarded.
just a thought, good luck.
jt

JaayTeee

oop's, after rereading the initial thread,
i figured out you don't have a efi,
they came out in 93',
is the timing advancing at all?
i had a 91' 502 mag. it had a " conservative"
advance curve in the module,
if i remember right, only 18 degree's
so when timing was set at
suggested 8 btdc, you only got 26 deg.
total advance,
i advanced timing to 18 degree's, which
gave me a total of 36 degrees full,
boat was similar to yours,
it really "waked up" the out of the hole performance.
thunderbolt IV ignition didn't use "detonation" sensors..
sorry on my first reply (like my wife say's, i don't pay enuff attention )
ggod luck,
jt

Holy Smokes

thanks JT... My module has a 20 degree advance. I'm not 100% sure if the timing is not advancing or what. As it was described to me the thing won't hold the timing and is very erratic. I agree you can "cheat" a little and set the timing forward as you did, but from what I've heard you only want to advance to around 30 degrees or so. BTW you're right, no knock sensor.

500hps... thanks for the offer, but I think I'll stick with the basic Edelbrock package set. BTW... Welcome to OSO. I'm honored you chose my thread to begin your OSO life!!

Griff

KC, setting the timing up to 34* total is fine. Stock setting is 32* total.
If the timing is eratic and jumps around like you say, I think you're on the right track with replacing the cam. I'd put $$$ on the gear being trashed.