The Stovebolt Site Forums The Shop Area Engine Shop GM HEI Distributor Shaft End Play

I've acquired a couple late 70s/early 80s GM HEI distributors for my 235 engines. Both have 0.125" shaft endplay, which seems a bit excessive. However, GM must have engineered this for a reason. Will this end play have any affect on engine timing?

I see that distributor shim kits are available. What is a reasonable amount of distributor shaft end play?

Thanks,

Don't know about others, and I expect you might get some varying answers on this. On some forums I participate in, this topic can draw some interesting responses. Personally I'd say .125" is too much by a good whack. I'd go for .010" and leave it at that. I've read timing can change 1 degree for every .012" of end play, so if what I've been led to believe, you're talking about allowing no more than 1 degree with .010". Good luck.

Won't the spiral teeth on the gear keep it pushed up against the bottom of the distributor housing with the engine running? I would probably add a thrust washer between the gear and the housing to reduce the end play a little, but in the real world, it's probably a solution looking for a problem. I'd be more concerned with the vertical position of the reluctor and the pickup coil teeth.
Jerry

Handy Andy Have made all my own HEI's I use 1/2 inch machinery bushings from the farm store,mostly important to have space up and down when it's clamped to the block,be sure there is oil clearance where your gear rides on the block. To avoid cap interference with the side of the engine I make an aluminum spacer to raise it up about an inch. You'll find sludge build-up on the shaft will make it hard to get apart,like for a pick-up coil change,once apart then you can clean it up.

John G Your right on there for HEI end play,with that .010 you can feel if there is clearance for oil at the bottom of the gear,haven't noticed any reason to spend 11$ for shim kit,grind out my own stub shaft,pin it to main shaft get a bronze bushing at the farm store it may do 2 distributors turn it to fit go to truckin !!

Handy Andy One other detail I find the later distributors with more electronics just muddy the water for our old trucks.Just the simple HEI is best now if you figure out electronics might work good but probably need computer input.

Yes, Jerry...but isn't there also the dynamic of the oil pump drag and other factors? Some of these can be surprising. 40 years ago I had a 235 I had just rebuilt which would not idle correctly no matter what I tried. Finally I pulled the camshaft thinking one of the lobes must have gone slightly wonky. Wasn't that, however. The thrust plate (normally is supposed to have .001 to .005" gap between it and the gear) was worn to the point where it had a gap of about .022". The cam was bouncing in and out enough at low rpms to make the timing swing in/out of range. I figured the design of the 2 gears would prevent that, but it didn't.

That's also why a small block V8 with a double row roller timing chain needs a thrust button on the end of the cam, and a reinforced timing cover.
Jerry

Thanks for the information. Some of the info I've read refers to the expansion of engine components due to heat likely taking up some of the end play. Also, the spiral design of the meshing gears should keep things lined up, but there seems to be some uncertainty about this. I'll be disassembling the HEI distributors for a good cleaning, lubrication, and reassembly. These distributors are good candidates for my 235s as both have passed some initial bench top testing. I plan to reduce the end play, being mindful of the need for lubrication and the vertical position of the reluctor/pickup coil position.

Thanks again,

I have run a lot HEI's on my distributor machine, I adjust the end play for .010" - .020" or enough for oil get into and around the bushing. The bushings are not a standard size, I order them for a High Performance Buick shop for a reasonable price. You can add 1/2" ID machinery shims or make your own, most of the time I knock the lower bushing out and replace it with new. I have seen them with the pickup coils way off center and still run OK, but I try to center them best I can. With the lower bushing out, it's easy to knock the upper one into place. With a good puller. you can get the bushings out and reuse them if you have to. The OEM lower thrust washers wear, so be mindful of that when cleaning and align the dot on the gear with the pointer on the rotor.

It takes a bit of creative machining, but I've built up a few distributors with a Torrington needle bearing at the top of the housing for a zero-wobble top end. It's surprising how inaccurate some distributors can get, either from wear or manufacturing tolerances.
Jerry

Handy Andy My local 55 year junkyard where they are true junkyard dogs,test HEI's this way-put 12v jumper cables on it handle it like a hot potatoe spin it if it pops and cracks is good. Best part is they turn you loose in the yard,covers about 120 acres,amix of 30's to current vehicles.

Joe H: I'll shoot for that .010" to .020" range for end play. Do you have a source that you can share for those bushings? I'll have to look these distributors over closely. Hopefully, I won't need to replace the bushings. I'm aware of the alignment mark and the rotor orientation. Good reminder, thanks!

Jerry: The needle bearing sounds interesting. However, the bushings should suffice for my purposes.

fixite7: You are very fortunate to have an auto salvage yard that not only has the parts you need, but they turn you loose too! The pick-n-pull salvage yards are long gone in my neck of the woods here in Iowa, or paradise as 52Carl fondly refers to Iowa.........right Carl? I suppose turning people loose in a salvage yard is a 'big liability issue' these days, or so I've been told.

My thanks to all,

Compared to Missouri, you bet.

http://www.taperformance.com/products.asp?cat=340

https://www.ecklers.com/catalogsear...em&rows=30&view=grid&start=0

Here is where I get my parts, mostly from TA Performance.

Joe H Hey say that again about align the dot with the pointer on the rotor !! Never heard of that yet,My HEI's mostly have the gear turned over then drill the roll pin hole...at random,shim and assemble put it in maybe shim with gaskets. Been a while cause mine are all running,winch truck set 5 years fired right up.

HandyAndy Yes it's great to have a junkyard where you can shop on your own,it's just covered with stuff!!

On the gear, there is normally a dot machined in to the side, this aligns with the rotor pointer. It aids the installer when aligning the oil pump drive shaft to the distributor gear drive. ( 99% of what I work on is Pontiac stuff, so this maybe related to them ) If you know where the dot and rotor are, you can turn the oil pump drive so they mess together with out rotating the engine or taking multiple stabs at it.

Here's a pic of the alignment dot.

I finally got some garage time in this afternoon. A local farm store had those 1/2" machinery bushings, so I filed them a bit to get the needed clearance. There are two shims placed above the distributor gear which leaves me with 0.010" of distributor shaft end play. This quite an improvement from the 0.125" that I started with........

Thanks to all,