The Stovebolt Site Forums The Shop Area Engine Shop 235 oil pump measurement help

I measured 4 different 235 oil pumps to see if I could spot a problem. I measured from the center of the mounting hole in the pump to the top of the oil pump casting. I measured my old '54 pump, a '57 pump, my damaged '60 pump, and my new '60 pump. All of them were consistently around .630". Depth from top of casting to bottom of drive tang slot, diameter of driveshaft hole, pump body OD" etc was nearly the same for all pumps.

I measured the dimensions of the HEI vs the stock distributor, and all dimensions were very close. I then installed the HEI in the block, and the distributor gear was crammed down on the oil pump casting with not much endplay. I rotated the engine with the starter, and the distributor gear started to "shine up" the top of the oil pump.

Haven't checked to see what the stock point distributor from my '54 235 does when I install it and do the same test. I've never run this engine with this point distributor either. The '60 engine's original distributor was lost long ago.

I would like to eliminate a dimension of the engine block as a source of the problem. I need as many of you as possible to pull your 235 distributor, and measure from the distributor mounting surface of the block, down to the top of the oil pump casting as installed in the engine. If that dimension of my block is too small, it could cram the distributor down against the oil pump casting.

My latest theory:
The original points type distributor has a movable clamp that holds it in. I'm thinking that my block could be out of tolerance. It was not a problem in the past because the mounting height of the distributor could be adjusted by moving the clamp up or down on the distributor shaft to provide some end-play between gear and pump casting. The mini HEI assumes a certian block dimension there, and could cram the gear down on the top of the oil pump if the block is out of tolerance.

thanks guys

Chiphead

Chip,back "our" guess at the problem? Machine off the retaining ring on the mini HEI, and use a 235 style hold down, no need to do anything else.That's why the stock type distributers use the "adjustable" hold down, must be a difference there from block to block . It may also mean other engines are going to be destroyed by that terrorist distributer design.Clearances stacking up wrong is a killer.

Chip, I'll measure my '57 block and dist tonight.

Tony,

My only problem with the stock hold-down is the slop and wobble inherent in it. I know, I know, the car's not doing much else on jackstands.
How about shimming the HEI distributor with big washers? I've got a few that will fit well under the stock retaining ring and are .115" thick each.

Is it OK for the gear to ride on the pump at all? Even with one .115" washer, the gear was still contacting the pump, but not crammed down on it. Gear geometry looked much better.

Josiah- lookin' forward to an actual measurement.

Thanks guys

chip

Chip, just make a hold down bracket like this one here on this 250 HEI I used on 235-261 engines.I redid a bunch of these a few years back.Never got a complaint, but on my own engine, the top bushing failed allowing the shaft to drop down ,grinding up the pick coil.Just damaged the distributer, no problem .I think the top bushing wasn't up to thrust load, I have no idea if the 230-292 distributer gear drive thrust is up or down.Of course it may have just failed on its own.Whenever you use a non original part, things can happen.
clamp

Chip,
I measured my 235 block and I found the top surface of the oil pump to be about 3-1/64" below the machined lip in the block. (It was kind of hard to see down in there because my block is parked under a workbench)
The 1/64th came from where the gear wore into the top of the pump. It looks like new clearance should be 3" exactly. Note that this is a '57 block with the large journal cam, so I don't know if the '54 with its small journal cam was any differant. I'm pretty sure this is a stock cam in this engine, and it is a truck block with solid lifters.
There is another 1/16" to the outer machined surface. The shoulder machined into the block is what the mounting bracket/clamp rides in. The top of the pump and the gear seem to have been in constant contact over the 20k miles+ that are on this engine, a '57 block that may have been rebuilt at least once in its lifetime. The distributor itself shows very little wear although you can tell from the gear which way it rotates- there is tooth wear on the driven side of the gear and shiny spots on the driving side of the oil pump tang. The gear is installed so the long shoulder is on the oil pump side, although I expect that if you installed it upside down it wouldn't go in all the way anyway.

The distributor body itself has absolutely no shoulder to positively position it in the block. The clamp provides positive retention against twisting but little force in the vertical direction. The dist. simply sits in the block. It looks to me from everything I can see that the oil pump is supposed to provide the bearing surface for the distrubutor, and that the failure you experienced was either from lack of lubrication of that surface or from the thrust bearing in your HEI distributor providing too much downforce on the gear/top of pump. I think that if you re-machine the HEI so it can use the original style clamp and replace the gear and oil pump you will be fine. I also noticed that there is a flat machined into the dist with an oil passage to allow oil in/out of the bottom bearing in the distributor. I can take some detailed pictures of the distributor if you like. I can also try to take a shot down into the distributor hole.

The '50 shop manual states (for the babbit pounder) that "The distributor housing is designed to pilot down into the right side of the cylinder block which supports the distributor and provides a bearing for the distributor shaft." That seems to indicate that there is supposed to be thrust on the oil pump but yours must be too much.

Oh yeah, and the oil pump drive tang on the distributor shaft does not bottom out in the oil pump, so the oil pump gears are not taking up the distributor's thrust.

Josiah- Wow, thanks. I was afraid nobody would take the time to measure this. So judging by your block, a typical distance from block deck to oil pump casting is about 3 1/16". I assume this should be about constant independent of year.

On your dist gear, where is the wear on the teeth? Is it centered on the teeth, or moved up or down from center? My HEI gear shows wear above the centerline of the gear.

I plan on checking this in my '54 block, and my '60 block (in car) to compare the results. I'll also measure from clamp to bottom of gear on stock dist, and retaining ring to bottom of gear on HEI and see where that comes in.

I can only assume that my '60 block will have a smaller measurement than your block or my '54 block. I'll post all the results for comparison.

Tony- What is the shaft diameter on the 230-292 dist shafts? The stock 235 dist has a bigger shaft diameter than the mini HEI. The stock dist shaft fits much closer in the stock 235 oil pump casting. I'm worried that using a clamp with a mini HEI could allow deflection of the distributor. The shaft could wobble around while trying to turn the oil pump, causing other problems like strange gear wear or further contact between distributor parts and pump.

muchos grassy-[censored]
chip

The wear is perfectly centered on the teeth on the driven side of the gear.

Chipper, the 235 and 250 HEI shafts are both .490. A 235 distributer body where it slips into the block is 1.060-.062.The distributer must be a reasonably good fit into the block, the clamp is to prevent it from rotating only.

The HEI body is machined to fit decently in the 235 block, but its shaft is .410" or so... Smaller than a 235/250 dist.

Then it's sitting down too low....

Right?

I would try shimming it higher with the washers you mentioned.

.02

Talked to TomL again yesterday. The gear that is used on the HEI is from a GM 'iron duke' 4cyl. The bottom of the gear is custom machined to shorten it, then it is installed on the modified 2.8V6 distributor shaft. I'm gonna take several measurements this weekend, and discuss the results.

Be sure to tune in, Same bad time, same bad channel.

chip