distributor gear failure

Slide · #1 (**permalink**) 02-17-2002, 01:01 PM

Well this is discouraging. What can cause 7 to 8 teeth on the distributor gear to fail within 20 min. of initial start-up? 2 teeth flat with chips and distortion extending equally to each side for about 3 teeth. Ford A351 flat tappet cam and duraspark dist. I used plenty of ARP lube during assembly. The cam gear does not seem to have any damage from a visual inspection down the hole. Is there something stupid I could have done during assembly that could cause this? Any suggestions would be greatly appreciated.

greenwater · #2 (**permalink**) 02-17-2002, 01:40 PM

I'm not a great specialist or mechanic but had made research about distributor gear and here what I learned. There are three type available: steel,iron and bronze. Bronze is for steel cam (like most roller),it won't hurt the cam gear but will wear-off rapidly (just about gone within 2500 miles).
Iron gear should be match with iron cam...then none of those gears will get dammaged.

Steel gear should be matched with steel cam.

My understanding is if iron is matched to steel the iron part will suffer dammage being more brittle.

What is intricating in your case is you mentioned having a flat tappet cam....that should be an iron cam isn't it? Then if a mismatch was the case (a steel gear on your dist.),then it should be the cam gear suffering ....

So we are left to think that your cam is steel and your dist. was iron...check with the cam manufacturer if its an iron or steel one that should help you choosing the right gear for your dist. You can get the gear from ford motorsport retailers they have the three types ,both for 289/302 and 351 (different diameter).

Now I am soon to fire-up my engine with a steel gear after going through two bronze and getting tired of them. All I wish is I made the right choice of gear to go with my steel billet roller...

P.S. I believe that some refer to iron or cast gears ...just different words for the same thing.

Slide · #3 (**permalink**) 02-17-2002, 02:35 PM

Thanks Greenwater, but I'm pretty sure both of these stock ford gears are iron and even if not 20min. would not cause catastrofic failure of the dist. gear. Either I had a defective gear or I missed some critical step or check during assembly.

Double Venom · #4 (**permalink**) 02-17-2002, 02:42 PM

Clyde,
All I can tell you is to check the gear material. It is critical. You are not the first one to wipe a gear in 20 minutes or less!

DV

PS..I know it's a lot of work, but trust me. At the minimum, pull the pan, pull every rod bearing, clean before re-installing. Would be wise to pull the intake and go through every lifter also. Like I said, lot of work, but it is necessary if just one tooth got ground up.

Slide · #5 (**permalink**) 02-17-2002, 03:08 PM

Thanks D.V. looks like I wont be on the road soon

Jack21 · #6 (**permalink**) 02-17-2002, 09:28 PM

Thinking the oil pump might have something to do with this. The major load on the distributor gear is the oil pump. If the cam gear - distributor gear were mismatched, one would think there would be even wear all around. The failure as described was a group of teeth together sheared off. If the oil pump injested something that would make it stop turning, or a major oil flow obstruction occured in the engine to cause a severe hydraulic load, the weakest link in the chain that would break first would be the pump drive shaft, or the distrubutor gear.

Put an oil pump priming tool on the pump drive shaft, and see if it turns. See if it turns with equal resistance with a full rotation. If it doesn't turn at all, or binds in one spot, pull the pump out and find out why. When I pre-oil an engine, it's not uncommon for the drill I use to smoke and get hot. The oil pump uses a lot of torque to turn it, but it should still turn freely.

Just a thought. Don't want to do all that clean up and have it happen again.

Steve Dickey · #7 (**permalink**) 02-17-2002, 10:10 PM

Clyde,
It's always darkest before the dawn. Hang in there good buddy, this too will pass. I'm with DV, I would blow that puppy apart and clean house. It may save a lot more time and effort in the long haul,not to mention peace of mind.
Good luck, Steve D***ey

Hank Dondero · #8 (**permalink**) 02-18-2002, 04:40 AM

Suggest you check the type of oil pum and verify the bypass valve is operating properly.

I lost a dist. gear/cam shaft due to a high volume pump installed in a place where a standard should have been used. In addition, the bypass was very resistant. Checked a new pump out of the box and the bypass was frozen. HS!

I had steel gears and a roller cam.

Hank
FFR 111776-II

Double Venom · #9 (**permalink**) 02-18-2002, 04:54 AM

Excellent point Jack, and Hank...

When you do this all the time you (I) just assume that, checking the pump would be the 2nd to do thing on the check list. Not worth mentioning category so to speak. I've got to remember a lot of guys don't do this everyday!

Somebody re-heat my plate of Crow please. Time for a few more bites!

DV

P.s. Jack, I use an old Black and Decker 1/2" drill for priming, no smoke out of that baby, but you'd better be hanging on if it locks up!

rldunn7 · #10 (**permalink**) 02-18-2002, 08:17 AM

Preoiling the engine with the BOD(big old drill) would probably given you an indication of a problem. I cavitated the oil pump and broke the shear pin in my motor.....makes for an interesting roadside repair...hope you can get all the pieces of metal out of the motor....just take one of those small pesky pieces to jam up your oil pump....high vol' and good oil make 'em run all day....good luck!

dscott · #11 (**permalink**) 02-18-2002, 09:18 AM

This is a problem I fought for years and finally resolved. From what I know the only cams that cause this problem are the Ford 302 and 351w. Most cam mfgs buy their blanks from 2 different companies so the brand typically doesn't matter. The problem we discovered was the cut of the gear on the cam is to sharp. The only way to fix this is to burnish the cam gear on a wire brush before you install it. If this isn't done you will eat distributor gears for awhile. The first one will usually go right away and then progressively get better. After about 5 gears the problem will go away. I can't tell you how many years we fought this with no help from any mfg. I always got the same answer, don't use a high volume pump and use plenty of lube, or the distributor gear is not at the right height. I've tried many different brands of gears, changed cams, distributors, you name it. The fix was as I stated. Since I started burnishing the cam gear I have had no distributor gear failures in 4 years.
Don

Jack21 · #12 (**permalink**) 02-18-2002, 10:09 AM

Hmmm. Now they tell me. Even on grocery getter rebuilds I'll use somebody's (usually Crane) mild grind, not a factory replacement. From now on, I'll burnish the cam gear before install.

Guess I oughta pick up a couple of distributor gears as service replacements at plug or oil change time before thinking I'm home free with this. Definately at least one gear change before Carlisle or DVSFII.

DAVID GAGNARD · #13 (**permalink**) 02-18-2002, 02:10 PM

I have also seen this happen one time. The owner was given a distibutor fro a 351-C instead of a 351-W,it went down in the hole but the ditributor gear is a different size,so there was a bind on it when fired up and it went to peices in 15-20 minutes,just something else to double check.

David

CCX33911 · #14 (**permalink**) 02-18-2002, 03:15 PM

I lost a distributor gear on my FE. I had a couple of problems that added up.

1.) I installed a roller thrust bearing from Ford Power Parts for the cam. Unfortunately the supplied beautiful 12 point bolts were a bit too long and one of them partially cut off oil to the bottom of the distributor gear. Extra drag on distributor leading to more tooth load. Not sure if your motor has a similar oil passage setup.

2.) Distributor I used did not have proper end play. When distributor is installed in the engine the gear is supposed to bottom on a machined face just below the gear. As the cam turns the distributor it trust the gear down against this face which is feed from the oil mentioned above. If the distributor is not mounted in the right position the thrust will be taken by the little bearing in the top of the distributor leading to more drag and tooth load. Look for small shavings, etc. in the distributor under weights. This can be checked by measuring the dist. shaft endplay on a bench and in the motor. The endplay should be less by several thousandths when it is installed in the motor showing that the gear is contacting the thrust face. Who normally checks this?!?!?!

3.) Overly high initial oil pressure due to incorrect relief spring in by pass. Leads to extra load on teeth.

Add all of this up an you get a wiped out gear in ~30 minutes. I noticed oil pressure low and shut off motor. No damage, BUT fine particles of ground up teeth EVERYWHERE. I did a complete teardown and clean and rebuild. Lots of fun.

Tongue Pirate · #15 (**permalink**) 02-18-2002, 03:28 PM

dscott,
What exactly is burnish.

Slide,
Sorry to hear of your problems. Hope everything gets resolved soon. Did you paint the car yet???

dscott · #16 (**permalink**) 02-18-2002, 03:33 PM

I have a wire wheel setup on my grinder to burnish the cam gear. All you are doing is taking the sharp edge off the gear. The wire wheel works great for this.
Don

Tongue Pirate · #17 (**permalink**) 02-18-2002, 04:00 PM

Thanks,
I'll be sure to do this when I assemble the top end.

CCX33911 · #18 (**permalink**) 02-18-2002, 04:08 PM

I have read several places that you need to run a wire brush over any new gears (cam or dist.) to knock off the sharp edges, etc. I ran mine along the gear (with the grain). my new gears look fine.

Slide · #19 (**permalink**) 02-18-2002, 05:14 PM

Upon closer inspection, the distributor gear showed circumferential wear with chips starting at the bottom of the gear and distortion of the pitch. This probably began with initial startup until the weakest gears failed. I don't think that it was related to a seized pump because the roll pin did not shear and the pump still turns through 360 deg. Until the post by dscott I thought that there may be a different ford gear for the a351 cam but maybe not. When I pull the motor I will remove the cam and burnish the gear if it appears undamaged. Thanks to everyone for their assistance and kind words. It's nice to know that one is not alone in this universe.