New Cam for 502 Mag
 

I've been chasing an ignition / fuel problem for half of the last season. I finally gave up and took the boat to a local merc tech. They chased all the symptoms, as well. I replaced the cap, rotor, pickup sensor, plugs, wires, coil and fuel/water separator (just in case of bad gas). The merc tech rebuilt the carb, checked the module and replaced the distributor gear.

Now I'm down to replacing the cam, timing chain and sprokets. The merc tech will just replace with the merc factory specs. Is there any other "fairly stock" cam I should look at? I want total reliability, reasonable price, and quick delivery. Not looking for big HP upgrade packages, just something that will make it run strong and reliable. The boat will probably go up for sale this spring, so performance gains are not necessary. Engine will idle smooth, just way out of time and will not advance like it should. The rest of the engine is bone stock Gen V with 410 hours, except for a electric fuel pump and K&N arrestor. The boat is a '92 Baja 240 Islander, Bravo 1 (1.36) approx 4,200 lbs. I've previously had this boat up to 68 gps at 5200 rpms w/ 21P Mirage. Some say I should be faster.

Open for suggestions. Thanks.

Camshaft
 

I really believe that a good camshaft for use as a stock replacement is the Edelbrock Torker Plus. I have used it on many rebuilds such as yours and it really works great. It is just a little more powerfull and works well with the 454/502 Magnums valve springs and non adjustable rocker arms. It is also very reasonably priced. The part number is 5062.
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Thanks for the input Dennis. I've located the cam and was wondering is the Torker Plus a direct replacement for Merc #431-9830? Initially, looks like a huge savings over the Merc stuff (Duh!!) and the timing chain set for about $50 is about half of the Merc parts.

Anybody else have some packages that you've used with success?

Ive used the torker cam for years in numerous engines with good success. Break it in properly and your good.

B4 you go to all the work replacing the cam, I'd be looking at ignition again. You say that the module checks out, but the timing doesn't advance. With the Mercruiser ignition, both of those cannot happen. It will either advance or it won't. It may however act up when it gets warm.

How was the module checked? What is your base timing and what is it at full advance?

Have you checked to make sure the balancer isn't spun. Something does not add up and its very rare that you can wear out a BBC timing set in a boat in 400 hours.

Rod

KC, so the Merc tech said he didn't know WTF was wrong????

Why did he replace the dist gear??? If it was worn that badly, then chances are the cam gear is just as badly worn.

I had a similar problem in drag car before. We'd set the timing, put a load on the engine, and 5 mins later the timing was off again. It was bad gears on the dist & cam. Not sure which one actually failed first.
It isn't that hard to check the cam gear w/o pulling the cam. Just pull the distributor and look down the hole with a light.
If the tech thinks you've got something wrong in the valve train, he should have run a vacuum test and there are specs in his manuals to tell what the readings should be.

Griff has a valid point about changing the dist. gear. If it was worn enough to replace, the cam gear might be damaged as well. If the dist. gear was changed because it was actually bad, you should also be looking at the bushing in the end of the dist. Its probably worn and should be replaced as well, otherwise you'll be right back where you started.

If you post actual timing checks and testing procedure, we may be able to offer some more insight.

Rod

rpm... to check the module, he installed a new module and had the same result. Therefore, my module should be OK. I regards to the balancer, I'll ask. How is it that they "spin out". I assumed it was a solid piece.

Griff... I failed to mention that he replaced the distributor gear because there was about 3/4" of play in the rotor (rotated back and forth). He inspected the cam gears and stated that they were "like razor blades". I took that to mean that they were worn as well. He had hoped that replacing the distr. gear would suffice, but in reality it still did not cure the timing problem. My thoughts are that the cam gear is worn as well.

I'll also ask about the vaccuum tests and be sure that it was done also. I'm not sure of the actual timing checks and testing procedure. It really surprised me when he told me that the cam had to be replaced and that he was only going to charge me for the cam replacement and not all the exploratory work. (no less than 12 hours). This guy has a small shop and is very trustworthy. I want to keep him happy and I feel he want's to do the same for me. The best part is is that his shop rate is only $40 per hour!! I'll save about $300 if I buy the Edelborck parts online and give them to him to install.

Cam gears should NOT be sharp "like razor blades" It sounds like the cam gear is worn. That would also contribute to the play in the rotor and give timing readings that jump around a few degrees. If its bad enough, it might jump a tooth hear and there too and really screw stuff up.

My thoughts exactly.
Vaccuum tests were completed per merc rec's.
They'll be removing the back seat and opening the front of the engine in a couple of days to determine what will need to be done. From what they tell me and from the knowledge of you guys, tells me I'm in the market for a new cam. That could be the only remaining thing... right?!?!?
IF that's the case, what would cause the cam gears to go within 400 hours? Is this typical? Should the distr. gear been replaced prior?
I can replace the cam and timing chain assembly from Edelbrock for the same money as replacing just the cam from Merc. Regardless, the cam from Edelbrock (they say) requires replacing the sprokets and chain with p/n 7810. The same parts from Merc run about $450 versus about $185 from Edelbrock. Is this legit? Is there any reason why I should go with merc parts in a stock motor?
Questions, questions questions....

Mercruiser/GM engine parts
 

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

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;) )

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. :rolleyes:

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?

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

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

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:o on my first reply (like my wife say's, i don't pay enuff attention :rolleyes: )
ggod luck,
jt

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!!

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.