Distributor Gear Failure on 454 Mag EFI
 

Was wondering how many other people have had distributor gear failures on their Merc. "Black" motors (454 mpi, 454 mag, 502 mag). It looks like the distributor gear got chewed up pretty badly this past weekend. I pulled off the cap and was able to turn the rotor about 60 degrees rather easily.

The motors are '99 Mercruiser 454 Mag's and have about 150 hours on each. This was the first outing this year, and it only last about thirty minutes. Running fine at 3200 rpm on minute, then instantly died. I had the motors up to 5400 rpm for about 60 seconds shortly before the gear failed. Anyone think this is too much RPM for a stock 454 mag distributor?

Finally, what are my options with replacing the worn gear? Does anybody offer a replacement gear, or am I stuck buying an entire new unit from Merc or another after market manufacturer?

Any help or advice is appreciated.

-Bayley

The gear is different, the merc/delco voyager has a smaller shaft and uses the appropriatly smaller bore in the gear. The gear you need looks like steel with a silver color plating [melonized? sp?]Anyway I went through this on a 99 502 and was shocked that they weren't the same. I beleive the stock roller cams in these engines are all steel, so I would stick with the stock replacement as you will never see 150 hours out of a bronze gear, IMO. My Chevy dealer couldn't I.D. the gear I had, but they cant do anything without a part #. I lost my gear because the dist. hold down clamp wasnt seated against the distributor properly. Like Formula said, now you can worry about gear additive, and How did you rev your motors to 5400? Good Luck

Thanks guys,
I hear ya about the "No Part Number, No Cooperation!" I have an old Datsun 260Z with a SBC under the hood and have always had a fun time with the parts counter guys. One cowboy even asked for my VIN number to verify what I told him is what I really needed. :rolleyes:

Anyway, the motors have a set of Whipple's on them. One of the feaures of these kits is the stock fuel cut is raised to something rediculous... 6500 RPM or something. The Whipple ECU then limits the spark timing to 5400 RPM.

Not sure what to do about the old pieces of gear in the pan. I was hoping I would hear: "Don't worry about them, tiny metal pieces in your oil is actually a good thing!" I guess I have to face the obvious... :(

I hate to mention this but did you ckeck your cam gear. Sometimes they get damaged also. Lets hope for the best. :)

I have never heard of anyone having this problem with eating gears. Has anyone else seen this? Should the gears just be changed at 150 hours? Mine has 170 hours with no problems. I think I just jinxed myself.:mad:

Formulafastech and Liquid Lounge are both partially correct. The gear is a standard GM gear, part # 10456413. It is a Melonized (spelling) gear for steel roller camshafts. Never heard of one going bad. Typical reason for gears going bad is too high of oil pressure or to thick of oil, or a combo of both on a cold engine. In my other life I race Buicks and this is a typical problem with them, but not with a BB Chevy..... DO NOT USE A BRONZE GEAR. Hope this helps.!:p

OH yeah, Blueman is prob correct also, your cam gear is more than likely shot.... No worries, the stock GM/Mercruiser cam is available brand new from www.competitionproducts.com for something like 39 bucks. They buy a bunch of Mercruisers stuff....Cam gear is about 25 bucks. Happy shopping.!:D

Something else you need to check is the alignment of the intake. It can be off by a small amount and wear out your bushings. Does the dist.shaft have play in it? If the shaft is skewed it will wear both.

Before you install the distributor, see if you can turn the oil pump with a screwdriver. I bring this up because had an engine once that ate part of a valve spring shim, lodged in the rotors of the oil pump, that's what ate the distributor gear.

Update!

Pulled the dizzy out last night and found one seriously chewed up distributor gear. Cam gear looks great, Oil pump smooth as silk. I'm glad it was only the dist. gear, but am still confused as to why. For now, I'll just assume it was a casting problem at the factory and cross my fingers it doesn't happen again.

Thanks everyone for the advice.

Ok ! Do an online search on melonized and you will find out it's basically case hardening.
The gears on the cam are hard steel like the rest of the cam. You should not have the problem with the Melonized gears. There were alot of valvetrain problems with the earlier Roller motors like yours. This is just another one of them. Believe it or not, Gm and Mercruiser learn along the way. Sometimes in this process Mercruiser learns and Doesn't get the fix right away from GM or the right hand doesn't know what the left hand is doing. The 10456413 gear is too big for My Delco Voyager EST distributors. I'm going to buy a Msd 08360 for a 502 I'm doing. I think after a certain time all the GM gears were melonized. I wish I knew what markings or details other than color came into play. BBB

Correct part number
 

ACDELCO 10493532 Silver gear. Rock Auto has them $37
That Msd number was a Whole Dist . I may still try to get a Msd Gear at the speed shop if I can get one that fits.
I have to Mic the shaft. It's late I am tired, Ran broke in and finished another installation today.

Wow, way to bring back a post from the past. ;)

Thanks for the update though. I've been contemplating replacing the dizzys with MSD units for a while now, but have otherwise been running stock MerCruiser distributors.

FWIW: I replaced the bronze gear with a factory replacement gear and haven't had any problems in 8 years. :)

I've got a pair of MSD billet distibutors in the swap shop.
MC

Hey Guy's Im new here. I buy 1987 aquasport tournament master with twin mercruiser 454 straight shaft engines. When i start drive from the long island to the Brooklyn, somewhere in channel i hit bottom because the shallow of water. It was noise and also lost half of oil from the left engine. After that cant start engine because no more spark in distributor. I mean when i take out distributor from the engine i see that there isn't cam gear in it. Anybody knows what happened and whats the solution?

I read that cam gear break causes may be high oil pressure/ thick oil / cold engine with high RPM or all of this together

SOS! Please help if anybody knows anything about my case.

better pull that engine and take it apart. Those pieces went somewhere. I agree all the above. Don't need more than 10-40 weight and oil takes like 10 min to get up to temp. If your lucky you will just have to clean the pan. If the pieces got between the roller lifters there might be damage. Pull pan check bores ,piston skirts and oil pump. Take oil pump apart. Could be damaged

Thanks. As i know gesr replacement is possible from the bottom pan side but for me much easy if i take out apart because of the weight of engine. Its big block so should be around 1300 lb with transmission. Do u know whats the just block weigh if i take out everything except it.



Most important thing is that distributor shaft or gear are without any scratches. If i lost cam gear why didn't damage distributor ?

Is it possible to see cam gear from outsidr or it just located under hole.

Gear is on distributor shaft and camshaft. Camshaft gear may be damaged also. Which means pull the can. You can see if can gear is damaged by looking down thru distributor hole and rotate engine to see th whole gear all the way around it. Something happened don't take anything for granted.

I know when you buy a zz502 or ho454 cam thew say you hafta buy the melonized gear. That may be true of EVERY stock roller GM cam. even sub-500 lift ones. You would think in that case every boneyard distributer would have the hard gear.

You may want to take some pictures and post them of your distributer. You may want to pay for the membership so people can see and help you.

big block is about 800 -900 lbs assembled

Distributor is like brand new. Nothing happened with it while engine doesn't spins it.

I will go in marina later today to do some electrical work and try take some pictures.

Im not mechanic but fixed almost dead engine on my second boat which works perfect now.

👍just keep in mind those pieces can cause catastrophic failure. You have to take the oil pan off . And don't flip the motor when you do it .all the pieces will fall towards the top. The new melonized gears come with extra material on them and will most likely be tight against the distributor housing. The gear needs to have about .010 play between it and the small wear plate at bottom of housing. You can do this at home , it takes a little time and finesse but not hard to do. Also there are 2 different diameters you can get. I think it's. 491 and .500

Take oil pan off on the place? Im not sure if its possible but i try to do. At least i will know if there is any broken pc of gear.

There where some Crane hydraulic roller cams dozen years ago or so that weren't heat treated correctly and the cam broke right before the cam gear section. So, everything spun but distributor.

while on engine stand take pan off without flipping engine over. You going to have pull engine

[QUOTE=SB;4586211]There where some Crane hydraulic roller cams dozen years ago or so that weren't heat treated correctly and the cam broke right before the cam gear section. So, everything spun but distributor.[/QUO
he said distributor gear was gone? Sounds like it broke in half and went somewhere unless just the teeth broke off

so is distributor gear ok??

Yes without scratches but im going to check everything double before start remival etc..

oh. All intact. Gear still on distributor shaft. Maybe just a broken split pin on the gear. It's a shear pin goes thru the shaft and gear

It's a hard read, so I just threw something that has happened against the wall. :)

Wow maybe u are right and its broken pin on the distributor gear. I will check it!

lol post some pics like he said. The gear could be spinning or something wrong at top of distributor

I buy cam with display in home depot and going to see what's going inside... Checked distributor second time, pin is on place.

ok, this is outdrive boat, correct? you need the pan essentially off to get timing cover off. if you have a car cherry picker, you can get it up enough to get pan, timing cover, and rotate motor till cam comes out. but if this is the hard cam gear, chances are cam is ok. just eats every dist gear that is softer. what gen motor? might be able to shine flashlight down distrib hole and crank motor to check if gear is ok, and turning. but if pin breaks, it retards cam 4 to 6 extra degrees, till the bolts let go.

No sterndrive. Its straight shaft thats why i hit bottom.

Ok, looked at pics of your boat. You will have a very hard time lifting that motor yourself. Weight for block-heads-intake is about 700 lbs. 900 with trans still attached. Engine is dead center in the boat. You need a boom truck to lift engine AND you need to replace or repair the 1 prop you used as a depthfinder. Props are not very good depthfinders. This boat has to come out of the water at a marina that can lift the engine out for you.
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Thanks. I have a same plan. In Marina they have big forklift so it will be very easy to pull out engine .

Start looking for people who can repair that prop now. You don't need to pull the boat, send prop off, repair engine, and still be waiting for the prop to be done...

do you think it's the timing chain?? Ouch.