Engine and Transmission Tech

Jim, That sounds fair.

Here is the latest CAD..
The beehive Comp 26981 spring is shown on all (height is adjusted to suit.

The one on the right is the stock pre-1980 cap / retainer - note the beehive spring is overlapping as its designed for a 1.25 spring.

The Comp 712 (I just realised I still have identified as 980) is pretty much the same as the stock one; it just sits a little higher (see previous pics).

Both the right two would need (for a 1,70" seat height) the spring pocket lowering by approx .142"


Middle pic is a proposal I had to modify the Comp 712 (again, wrongly identified as 980) to take the beehive spring. I have a friend with a CNC lathe that could be set up to have a mandrel chucked up, and machined with a 11-degree taper, and threaded, such that it can repeatedly machine these to suit. This would need 0.105" machined out of the stock pocket.

The second from left pic is just a reference, of the comp 795 retainer - obviously wouldn't work as the angles are not matched,

The left pic is the Comp 795 modified to 11 degree. As this would raise the height a little more, so needs only .072 removed from the spring pocket.

The next post will have all these pics (except for the stock retainer as this is pretty much the same as the 980) in better detail.







Edited 2 time(s). Last edit at 01/21/2023 10:36PM by turbodave.

Close-up pics for reference.

The last one is the modified 795. The real question, is what are the thoughts on so much of the keeper being outside of the retainer?
See the following post for a more detailed image with dimensions (only four images per post permitted)...









Edited 2 time(s). Last edit at 01/21/2023 10:14PM by turbodave.

As can be seen here, the top 10 thou and bottom 20 thou of the stock rover valve locks / collets have a slight chamfer, so you already lose contact surface area. But still with the modifuied 795, you would have just under 70 thou sticking out the bottom in fresh air. Is this bad? I just don't know....

As always, click on the image and it'll become a lot larger...




Edited 1 time(s). Last edit at 01/21/2023 10:18PM by turbodave.

Dave, I like the 980 modified the best. On the 795, what bothers me is the valve tip is so close to the retainer. If it was milled flat on top it would be better. The keepers are a lot longer than most and the part below the retainer won't hurt anything.

Hey Jim,
Well maybe here is something a lot simpler.

If we chucked up the comp 795 in a CNC lathe on the 0.639" dia, and located up to the spring face, it can be used to bore the angle to 11 degrees and face the top, and it'd be quick and easy to do all of these.

It will still need some material digging out of the heads, but that's not a surprise....

I don't really see any problem with the 795. As long as the valve tip sticks out any above the retainer nothing is going to hit. The part of the keepers that stick out below won't hurt either as long as they don't hit the seals.

Jim

Well, I guess I’ll speak with my local shop and see what they want to machine these on their Haas lathe. After initial set up we’re talking less than 2 minutes each, so can’t be all bad.



Edited 1 time(s). Last edit at 01/22/2023 11:20AM by turbodave.

Yep, let us know.

Jim

What is the diameter of the valve stem at lock ? The stem is 11/32" but it is thinner at lock position. I was just thinking if it would be possible to modify the smaller 7 degree 5/16 locks by removing the tang. In other words make it look like Buick/Rover lock ?

Jukka,

This is the dimensions of the valve and locks of the stock rover setup.

Jim,
Well the shop I spoke with suggested it would be a better idea if they did the setup, and I stood by the machine and ran the parts. Basically, for the price of a case of beer to them, I can get the 795 modified to the 11 degree angle. I'll obviously extend the offer to mod a set for you as well...

They also have a diamond wheel and spin fixture, so are happy to modify my manley 41824 seat pocket cutter to a slightly smaller diameter (it currently cuts 1.265 dia which is a hair too large for my liking) ... If you don't have a pocket cutter, you are likely to need one.....

So, I'm going to do a little more gathering of the other parts (like confirming and purchasing the springs I'll be using) but it sounds like we have a plan.

The ONLY thing I would want to add, is that based on the drawings, modifying the 795 to 11 degrees does reduce the cross-sectional area at the narrowest part from 43 to 37 thou. This then becomes 87% of the cross-sectional area it was previously.





Edited 1 time(s). Last edit at 01/23/2023 10:50AM by turbodave.

Jukka has a good idea! Here is a pic of a 7mm 10 degree you could use 7 degree also. You could use a retainer as a fixture and drill to remove the ridge. I think it should work fine.

interesting. Now I understand the thinking.
0.277 inch is 7.06mm so yep,

For a fixture, you'd need to stop them spinning, and maybe also add something to space them apart as they aren't meant to touch, and I'm sure unless using an end mill, they will drag up and out as soon as you drill them.

I feel that something more like this would be better, where you cut up half a retainer, machine it just a little past half way so the lock sits flush, and put it against a block (yellow) that has a notch in t for clearance (maybe tack them together at this point?) and use a clamp (purple) to hold them and use a 2-flute end mill to remove the offending lump?

What's the p/n for the 10-degree 7mm???





Edited 2 time(s). Last edit at 01/23/2023 11:23AM by turbodave.

Dave, here you go:

[www.racingsprings.com]



Edited 1 time(s). Last edit at 01/23/2023 11:55AM by mgb260.

Dave, I was thinking of just clamping the retainer in the drill press vice. Dressing a 9/32" Cobalt bit down to .278". I think the taper will stop any spinning. You just want to take the ridge off and hone it out a little. Once drilled, shut off drill, lift up and remove locks.



Edited 1 time(s). Last edit at 01/23/2023 12:15PM by mgb260.

I am sure if drilling as a pair you’ll want to put a known thickness shim or gauge wire between the two (on the flats) to space them apart, and press down to seat them and prevent spinning. Rethinking it, that would probably be pretty easy to achieve, just a little fiddly with the shim, but totally do-able. Doing as a pair would stop the drill walking and be a LOT quicker of course!

McMaster has metric colbalt drills I’m sure. I do have a few metric R8 collets so will probably just use my mill.

How great is this that the .277 is right there at 7mm?
Nice idea Jukka !



Edited 1 time(s). Last edit at 01/23/2023 12:14PM by turbodave.

That is what I hoped the TA locks were! Actually, if you use a 7mm bit and they are touching, they won't be when on the valve stem because it is slightly larger diameter.



Edited 1 time(s). Last edit at 01/23/2023 12:32PM by mgb260.

Good idea but it will be fiddly and tricky to do. That spacer between the two halves will have to be an accurate thickness so you don't cut into the rest of the bore and your clamping device will have to press the halves into the taper pretty firmly. You might make your spacer as a long tab that extends out the bottom and just drill away the center of it on the first set, then deburr and continue with the rest. That way the bottom part would make it way easier to insert as a single shim rather than two individual ones. Might want to make the shim out of aluminum.

But how to clamp it? Maybe something like a big nut that the retainer will fit into? Then a hollow bolt in the top that will press only against the keepers? Drill through the open center of the bolt. Has to be a step in the nut for the retainer to sit on. Draw something up Dave and I'll throw out some more ideas.

Jim

I'll throw something together in 3D to make it easier to visualise.

Based on my playing with locks in the past few weeks, I'd have thought we're only talking about 4-8 thou a side. That'd be not too difficult to cut into 1/16" wide strips. If cut to 3" lengths it'd be pretty easy to slide in there.

Jim or Dave, You guys can check the gap on the stock Rover pieces. For a shim, a pop or beer can is around EDIT.004 thick so a piece doubled would be about .008.



Edited 3 time(s). Last edit at 01/23/2023 04:29PM by mgb260.