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Bayley 05-28-2002 01:22 PM

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.


liquid lounge 05-28-2002 03:51 PM

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

Bayley 05-28-2002 05:59 PM

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... :(

Blueman 05-28-2002 09:43 PM

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

Vinny P 05-28-2002 09:48 PM

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:

Madmax 05-29-2002 10:29 AM

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

Madmax 05-29-2002 10:39 AM

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 for something like 39 bucks. They buy a bunch of Mercruisers stuff....Cam gear is about 25 bucks. Happy shopping.!:D

BOB ONEIL 05-29-2002 03:18 PM

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.

MKast 05-29-2002 03:30 PM

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.

Bayley 05-31-2002 12:38 PM


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.

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