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Life of bronze distributor gear?


jt1

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I am working on my car today, and pulled the distributor out. I was pretty surprised to see that the bronze gear is worn badly; to the point that some of the teeth are worn to a sharp edge. About this time last year, I installed the dist and gear, both new MSD items. I also changed cams at that time, to a slightly larger Comp solid roller than the previous cam. The previous dist, a GM HEI, had been in the car about two years, and the gear on it looked fine when I removed it, as did the cam.

 

Is this normal wear for a bronze gear? The previous setup looked almost new when removed, after two years usage.

 

Is my distributor running too high? The wear pattern is closer to the bottom of the gear than the top, but doesn't appear to be running off the bottom of the gear.

 

Worn cam bearings? They were new when this motor was built 3 years ago. I'm not running huge valve springs, Comp 977's, which comp reccomends for this cam.

 

Possible oil pump or pump drive problems? I'm using a high volume 4 bolt pump. Should I check it? Nothing showing up in the oil filter or magnetic drain plug.

 

This is my first roller cam motor, so I don't have any experience to go by. Any thoughts or comments?

 

gear.1jpg.jpg

 

edit: add crappy pic

 

John

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Seems to vary with the alloy of the gear. The one in my Camaro now has been in there a long time, but probably no more than 2500 miles. It is on an MSD distributor. The one before it looked like yours with only about 600 miles but was a .491 shat GM points distributor for what that is worth. What you need to do is figure out how much clearance you need on the gear, drop it in without a gasket and use a feeler gauge to measure. You may need to run a thin gasket or shim the distributor up to get approriate clearance. When I bought my roller there were no other options. If I had purchased one in the last 15 years I would have gotten one with an iron gear pressed on so you can run a conventional iron distributor gear. Crane says no on the GM melonized gear, or at best a "maybe" but they say the Ford OEM gear is fine with their cams. GM runs a melonized gear on their factory rollers(same with the FOrd, so I don't no why theirs is but the GM isn't small alloy difference I assume.), but they are cast steel and not billet. Comp was non-commital on whether the GM melonized gear would take out my cam, so I still have the bronze gear. But Comp has a new composite material drive gear that I think I will try. Costs as much as 3 bronze gears, but they say wear is virtuaylly nil. $100 is cheaper than having to replace a whacked billet roller that's for sure.

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When I was assembling my motor with a new roller cam and the required bronze gear (a first for me), I was told by an engine builder (HP and race) that the first distributor gear (being it was a brand new cam) would most likely last only about 5k miles. He said the next one would last perhaps 20K, and a third one a little bit longer but not much. The first one would smooth up the cam gear teeth enough that the subsequent distributor gears would last longer. It sounds like your experience may be proving him correct.

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Ugh. That's exactly why I'm looking at a billet roller cam with a pressed on cast gear. It cost's $55 more than an all billet one. I wonder what the wear chips from 1 or 2 worn bronze gears does to an engine. Hopefully you guys are running filters that will catch that stuff, and have plugged the filter bypass?

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Thanks everyone.

 

MikeC: Will shimming the dist up or down change the depth of engagement or just shift the wear patch on the gear? Mine looks like it is a little high, about the thickness of the gasket.

 

I estimate the engine to have about 2500 miles on it since installing the cam & gear. But about 1000 of those miles were hard ones in open track events, the rest street miles. I changed the oil several times, and did notice a brassy sheen to the oil. I also cut the oil filter open each time, and there were no particles in the oil filter. One tipoff I missed was as I was checking the timing before one of last years last events, I was getting 2 or 3 degrees of spark scatter. I should have checked it then.

 

Yesterday afternoon in a paranoid fit , I pulled the motor, tore it down and checked the bearings. They were fine, showing only a little wear. I've been chasing a persistant leak around the oil pan and this is a good opportunity to fix it.

 

I'm gonna try one of the Comp polymer gears and see how it does. I'll let you know.

 

John

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I think it will, just like a ring & pinion. I haven't done this in years, but this is what I recall. You want as much engagement as possible, but you do not want to bottom out the oil pump shaft if that is possible. What I did was drop the dist into the block and measure. I measured the gasket thickness and assume a 30% compression. I then added a shim to the assembly to give me something like .030 from bottoming out. I don't know where I got all of this, but it seems to have worked well in my motor and has been 16 years now.

 

Please post feedback on the polymer gear. That is the route I am considering. The distributor gear is the ONLY reason that I don't trust taking my car on longer trips without the old points distributor in the back seat.

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JT1,

 

Confirm part number on cam and make double sure it's a billet cam. I'm running a comp roller but it's not billet ALSO I heard that comp was putting on an iron gear for the dizzy to make it a better match ie no bronze gear needed. I'll probably be pulling the dizzy tomorrow night, that oil leak, although small is REALLY pi$$ing me OFF. grrrrrrrrrrr. My shiny engine is coated with a light film of oil, well I guess it wont rust.

 

ds

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I have been battling that problem for years in my roller cam 454. I have changed cams and gears many times and the problem didn't go away. I have been told that high volume pumps eat those gears. However, I now think that slight core shifts in the block durning casting cause the cam and lifter bores to be out of spec. That is why some engines eat gears and some do not.

 

It has nothing to do with your valve springs. The timing chain drives the cam and the cam drives the dist. and the dist drives the oil pump. The oil pump may be dragging. The pump needs the proper clearance between the pump lid and the pump gears. If the clearance is too tight the dist gear will be pushed hard.

 

Another problem I had was the dist. shims worn into the bronze gear which cause a bunch of end play in the dist shaft. This caused the rotor to either come up and hit the cap or fall down a far distance from the cap which screwed up the ignition. So I machined a pocket down into the gear and screwed down a thick dist. shim (0.060) onto the bronze gear (used 2 counter sink screws size 2-56). I made a "horse shoe" for the soft gear. I'm happy to say that this fixed the shim "digging in" problem AND the sharping of the teeth! I didn't expect to fix the tooth wear problem. I just wanted the end-play to remain constant. It has been over one year and the gear still looks new. I have been pulling the dist about every two month to check it. Before it would take a few hundred miles before the teeth worn out!! You might want to try it.

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dsommer is CORRECT!!!!!

 

After checking Comp's catalog and double checking with the tech line, my cam, a XR280R, doesn't require a bronze gear. It's ground on an austinite cast core, not a billet core. I ASSumed all the solid rollers were billet and needed the bronze gear. The appearance of the cam really threw me off, the entire surface was machined. Normally on a cast core cam, the area between the lobes still have a as-cast surface.

 

ds, you've saved me a $100 polymer gear and probably more grief in the future. Thanks a ton.

 

John

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YES!!!! HAHA That makes me feel GREAT!!!

 

I was wondering because when I was seaching for a solid roller myself, I had contacted CompCams concerning the bronze gear and they told me no need for it.

 

Now JT1 I'd like to pose a question to you...

 

I'm running an XR268 mechanical roller, 350 (.030 over) blah blah blah...

with a T-5 and a 3.90 rearend (R-200)

 

I feel my car is fast, quick, and has LOTS of power, scares the $hit out of me anyway.

 

You're going to be running or are already running that 280 cam. What is your HP goal? What heads are you running? What intake are you running?

 

I sit here and think, Man I could go a little bit bigger on my cam, run a different intake (Victor Jr) and make about 50 more HP OR add a 100 shot of NOS then I go drive the car and think to myself screw that idea, this things too fast as it is!!!

 

You go Boy!!!!

 

ds

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Guest Anonymous

I can give you a little info on John's power. I have an lt-1 putting down about 320hp to the rear wheels. John walks away from me in the straights. One fast car. Mark

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4 bolt block +030

Cola 4340 crank, 3.48

Manley 5.7 Hbeams

JE Flat tops, zero deck, 10.4:1

Trick Flow twisted wedge heads, out of the box

Comp XR280R, Comp promag 1.52 rockers, 977 springs

Edelbrock performer RPM air gap

Holley 700 DP, Choke cut, radiused & polished

MSD 6AL & MSD dist

Hooker block huggers into a single 3", double chamber flowmaster

 

No specific horsepower goals. Last time on a chassis dyno it pulled 352 at the wheels. I mostly open track the car, so no 1/4 times.

 

I'm currently upgrading to 197 Canfields and 1 3/4 S&S headers, and am pondering intake/carb. I'll probably stick with what I've got right now.

 

John

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Well it doesn't sound like I'm too far behind you except a little bit smaller cam,

 

350 4 bolt 30 over all casting flash removed inside and out (that's what the book said to do, I took it to the machine shop and the guy is like DAM dude you got serious with this thing, I polished the lifter valley with a die grinder haha :D )

Eagle SIR rods

Speed pro Teflon coated hyper pistons

Performer RPM gasket matched to heads

Edelbrock 750

Trick Flow heads with the larger springs (room to grow :D )

Scorpion billet rockers 1.5

Summit blueprinted HEI

Hooker block huggers w/2 1/2" into 3" pipe out the back.

 

Gotta get it to the dyno soon and see what kinda numbers she'll put down, I'm hoping for 330 or better at the wheels. Computer dyno showd 404 HP @crank with the parts I assembled. At least I havent blown it up yet, built it myself. First whole engine by myself ever... chest sticking out here

 

David

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Mark, I'm really looking for a durability increase rather than a big step up in power. The trick flows have eat the valve seals again, and the Hookers have several cracks in the collectors. I'm not at all sure the S&S's will work on my car since it's so low, possible ground clearance issues. Maybe it will be a little stronger, but probably nothing earthshaking.

 

I'm gonna try and be ready for the April T1 day; What's your schedule looking like?

 

John

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Nice setup John. What are the specs on the XR280? My cam is the 280AR street roller 280/280 236@.050 .550 lift and I lash at .020. My motor is mostly a 71 GM LT-1.

.030 with single trough TRW flat tops ~9.8:1.

GM Nitrided steel crank std/std

GM Pink Rods w/SPS bolts

Moroso pan,windage,pump,etc.

Crane Gold rockers

GM iron 492 heads

2.02/1.6 manley pro-flows

comp 950 springs 10 CC Superlocks

Titanium Comp retainers

Victor Jr.

MSD dist/6A

BG Stage III 750 dp rated at 1040 cfm :D

 

110 mph trap speed with my 3500# car suggests 360 rwhp. Which ain't so shabby for a GM iron head motor build twenty years ago! Just for giggles, I plugged the numbers in the computer, changed nothing but the weight by 1000# less and it puts the car in the high 10's! Your car should be their or low 11's. I'm interested to see how much power the heads are worth...if any.

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David: That's a nice balanced setup. Mine is on the edge of streetable, at least with the lightweight clutch and flywheel. You have to be just right to start off without killing the motor or spinning the tires. It would be a little better with a stock style clutch. Get it to a chassis dyno, tune the carb and timing, and let us know how it does. I bet you'll be pleased.

 

Mike: I have a ton of respect for the 292/492 heads. They are one item GM definitely got right the first time. I've got a set of 292's I would run except for the weight penalty on the front of the car. The XR280R is 242/248 @ 50, 570/576, 110 LSA, 016/018. It pulls nicely from 3000 to 6500, but has a pretty rough idle. It sounds good to me though!

 

The TF's are advertised to flow 235 out of the box, the Canfield's 260 with a "mild bowl blend", whatever they call that. No info on the Canfields out of the box. I may get someone to clean them up if i can find somebody interested. No one local has a flow bench to really check them out. They may help the car a little, but I suspect the limiting factor now is the exhaust.

 

John

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