distributer gear bottom to block clearance?

ChrisH October 19th 2021, 11:05 pm

so i have the following
roller cam bearings
steel cam
steel cam timing gear
solid roller valve train
bronze thrust plate
bronze distributor gear

HV oil pump
.0027 rods
.0031 mains
20w-50 VR1 oil

got close to 100 miles on the engine

i set the bottom of the gear to 4.002" from bottom of distributor - compressed - msd distributor and gear.
4.020 hanging.

gear teeth has some wear, at this rate may last about 300 miles.

the block where the gear rides has a modest bronze coloring so i know when its under load there is contact.
also there is a nice smooth wear on the bottom of the gear. (i do have Pauls small hole feeding oil to this surface)
also the thrust plate has wear from the steel timing gear. the side with the cam is clean. so i know the cam is thrusting back and down as expected.

the question,
when i install the distributor and push down on the cap i have .0065 gap between the bottom of the gear and the block.
if not for the bronze mark on the block i would move the gear a little lower and see if i could improve gear wear a little.

if 300 miles is the answer then that is the answer and dont really have a problem with that, just asking to see if anyone has an opinion on what this gear to block gap should be once in the block.

i realize i am using parts meant for the track on the street so high wear on sacrificial parts is expected to some extent.

thank you all.

chris

rmcomprandy October 20th 2021, 11:38 am

ChrisH wrote:so i have the following
roller cam bearings
steel cam
steel cam timing gear
solid roller valve train
bronze thrust plate
bronze distributor gear

HV oil pump
.0027 rods
.0031 mains
20w-50 VR1 oil

got close to 100 miles on the engine

i set the bottom of the gear to 4.002" from bottom of distributor - compressed - msd distributor and gear.
4.020 hanging.

gear teeth has some wear, at this rate may last about 300 miles.

the block where the gear rides has a modest bronze coloring so i know when its under load there is contact.
also there is a nice smooth wear on the bottom of the gear. (i do have Pauls small hole feeding oil to this surface)
also the thrust plate has wear from the steel timing gear. the side with the cam is clean. so i know the cam is thrusting back and down as expected.

the question,
when i install the distributor and push down on the cap i have .0065 gap between the bottom of the gear and the block.
if not for the bronze mark on the block i would move the gear a little lower and see if i could improve gear wear a little.

if 300 miles is the answer then that is the answer and dont really have a problem with that, just asking to see if anyone has an opinion on what this gear to block gap should be once in the block.

i realize i am using parts meant for the track on the street so high wear on sacrificial parts is expected to some extent.

thank you all.

chris

The bottom of that gear is supposed to ride on that block shelf, (presuming that shelf is not worn lower).

The Ford dimension is 4.034" extended.

Pushing on the cap does not push down on the distributor shaft.

ChrisH October 20th 2021, 4:41 pm

sorry i misspoke, i meant to say when i push down on the rotary button. yes pushing down on the cap does not affect the shaft.

BOSS 429 December 29th 2021, 1:51 am

The gear should never touch the block, there should be some clearance between the two

rmcomprandy December 31st 2021, 12:33 pm

BOSS 429 wrote:The gear should never touch the block, there should be some clearance between the two

I guess that Ford Motor Company has built a billion production vehicles with that being wrong...

BOSS 429 January 1st 2022, 12:38 am

rmcomprandy wrote:
BOSS 429 wrote:The gear should never touch the block, there should be some clearance between the two

I guess that Ford Motor Company has built a billion production vehicles with that being wrong...

https://performanceparts.ford.com/download/pdfs/DistributorGearInstallation.pdf

.005 min

As I said its not really supposed to rub on the block.

For a while years ago when I was taking a lot core engines apart Id pull the front cover first and slide a Feeler Gauge under gear, I FOUND .008 or more every time, didn't matter if it had 5000 miles, or 200,000.

rmcomprandy January 1st 2022, 12:25 pm

BOSS 429 wrote:
rmcomprandy wrote:
BOSS 429 wrote:The gear should never touch the block, there should be some clearance between the two

I guess that Ford Motor Company has built a billion production vehicles with that being wrong...

https://performanceparts.ford.com/download/pdfs/DistributorGearInstallation.pdf

.005 min

As I said its not really supposed to rub on the block.

For a while years ago when I was taking a lot core engines apart Id pull the front cover first and slide a Feeler Gauge under gear, I FOUND .008 or more every time, didn't matter if it had 5000 miles, or 200,000.

Looked-up a block print for a 351W, (I couldn't find one for a big block), and that dimension from distributor seat to that shelf is 4.040" +/- .001" so, that 4.031" to 4.038" with the shaft extended could be zero but, probably not.
I have always used that Ford distributor gear installation guide so, I thought it simply touched but, again probably not.

EDIT: went and read that print for an aluminum aftermarket 351W again and I missed a number. It was not 4.040" but, 4.0340" + or - .001", that tells me it is supposed to slightly touch or slightly not touch the block support.
The FORD RACING directions clearly says in their WARNING: that it is supposed to lightly rest on that support; that is what I always thought.

The actual Ford prints must give a different block dimension for a cast iron block..

aquartlow January 2nd 2022, 2:03 pm

Great info above!

ChrisH January 3rd 2022, 3:25 am

i do know this, if that dimension is a little too much it will shear the pin, repeatably.

like stated, mine has a clearance of .006. but after running there is a little bronze color on the block (almost like under use there is flex/stretch that closes the distance.

i did switch a to better bronze gear. i mistakenly thought MSD was decent.

engines back together, just have to put it back in the car. ill see how this one fairs.

thank you for the insight. it seems the answer is 0.000 +-.005.

if i reset this dimension i may set it like a bearing clearance (something like .003) as i have a small oil supply drilled under the gear.

snuff98 January 3rd 2022, 11:07 am

Heavy weight oil and a high volume pump is hard on a bronze gear especially in colder climates and engines with tight clearances. I left the 20w 50 oils and the high volume pump a long time ago with good results. I run a Kaase aluminum pump which is standard volume guts and 10w30 synthetic oil in the summer and a blend of 5w30 and 10w30 when it cools off.

ChrisH January 4th 2022, 12:56 am

i will work my way down on oil weight. i just knew i had built a somewhat loose engine and wanted to make certain i had enough flow.

it seems i have the gear height set about right, so now its just a matter of using a quality bronze gear and then finding the oil weight flow and pressure i need. at that point i have what i have.

68galaxie January 6th 2022, 5:59 pm

https://performanceparts.ford.com/download/pdfs/DistributorGearInstallation.pdf

WARNING: If the distributor gear is installed incorrectly, it may
be forced down against the support in the block or may be held
up away from the support in the block. Both conditions will
cause damage to the block and or the block and gears. When
the gear is properly installed, the cut on the gears and the
direction of rotation will pull the distributor gear down against
the support (distributor gear thrust face) in the block.

Pull up on the aluminum distributor housing and verify that you
can lift it up at least .005" while holding the gear against the
support in the block. This procedure will confirm that the gear
is not being forced down against the support and not being
held up off the support in the block

I believe the Ford depth of the bearing surface is 4.027"

Paul Kane January 13th 2022, 3:44 pm

In its STATIC state (engine on stand), the distributor gear is supposed to be set, during engine assembly, so as to be a few thousandths above the Thrust Boss that is machined into the block.

Then in its DYNAMIC state (engine running), the distributor gear is thrust downward and essentially "dances" on the Thrust Boss in the cylinder block.

So with the engine running there is a balancing act between the roll pin and the Thrust Boss, the two of them sharing in the drive load. If the gear is positioned too low during engine assembly the Thrust Block gets chewed up; if the gear is positioned too high during engine assembly the roll pin shears downward (not rotationally as mot people mistakenly believe).

ChrisH January 26th 2022, 10:55 pm

Paul Kane wrote:In its STATIC state (engine on stand), the distributor gear is supposed to be set, during engine assembly, so as to be a few thousandths above the Thrust Boss that is machined into the block.

Then in its DYNAMIC state (engine running), the distributor gear is thrust downward and essentially "dances" on the Thrust Boss in the cylinder block.

So with the engine running there is a balancing act between the roll pin and the Thrust Boss, the two of them sharing in the drive load. If the gear is positioned too low during engine assembly the Thrust Block gets chewed up; if the gear is positioned too high during engine assembly the roll pin shears downward (not rotationally as mot people mistakenly believe).

this looks to be exactly what i am seeing based on the bronze transfer on the block and the smooth wear on the bottom of the gear, as well as slight static clearance. thank you all for the insight

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distributer gear bottom to block clearance?

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