Hewland MK9 Pinion Layshaft Nut Torque

[Bob Coury]

Taylor says 115 ft-lbs on each, Tony Wilson site out of the UK states 120Ft-lbs on the pinion, and then 70 ft-lbs on the layshaft before lining up the split pin hole.


Regardless of the torque, what do you guys do when trying to line up the split pin. do you use Taylor's or Tony's as the min, then torque untill you get to the split pin hole, or back off until the hole?

[Garey Guzman]

On my DB1, I used 115# for both.

I think you can machine the thickness of a washer to get the correct tightening torque at the point the cotter pin lines up. Mine was right when I got it so I didn't have to do anything to it. I preferred to use a really thick cotter pin, nearly hole size but I had slightly smaller ones just in case something changed minutely (gear thickness stack-up).

[Brian]

I tend to use about 115 on both, but I haven't done those bolts up with a torque wrench in years. I just line the hole up, stuff in the cotter pin and done. Now, someone, sometime, had to trim the bolts (no washers) so that would work, but once it's done, it's done. The torque there isn't, in my opinion, critical like a rod bolt stretch is critical. It's important to have them tight is all. Trust me on this, the expense of having a pinion bolt back off is not to be sneezed at...new ring and pinion time if you run it loose for long.

To specifically answer your question on backing off, etc - as far as I'm concerned part of building a gearbox is adjusting the nuts so that the hole lines up with correct torque. So if your's don't then you should make that happen.

Brian

[Peter Horvath]

I agree with Brian on all points, except one: "just line the hole up".
The correct location of the big nuts, with respect to the hole, is critical. I will analogize it to the Moon (bear with me, I've had a couple of beers).
The new Moon begins as a sliver, then becomes big and round, then slowly wanes. Same thing with the big nuts. As they turn across the hole, the hole is a sliver, and you can't get the cotter pin in. When fully aligned, the hole in the nut and the hole in the pinion/lay shaft present quite a large target (Get it?...full Moon). In fact too large a target, and the cotter pin floats pretty free in this hole. Then as you continue to turn the nut (the torque is quite high at this pont), the hole turns back into a sliver.
You want the hole to present the snuggest fit possible for the cotter pin. Not only that, but you want the hole to be a "waxng moon", not a "waning moon". By that I mean that the hole is just startng to open up. If you go too far, the back side of the nut is holding the cotter pin snug.
The problem here is that the nut can start to move, clear through the "full Moon" position, and keep moving until the front side of the nut is up against the pin. Even though the nut is now where you want it to be, the nut has been moving, and its momentum can shear through the pin.
Don't get me started on the proper bend for the cotter pin. I'll be here all night...

[Craig Taylor]

We at TRE continue to advocate 115 ft lb. I have personally run as high as 180 ft-lb, but increaseing tensile load on the shaft reduces the torque capacity of the shaft itself. The old 70 ft-lb standard was recommended for the early MK4 gearboxes by Hewland; it is a carryover. What is important today is that enough torque on the nut be applied to achieve the tensile load to the shaft that will prevent flexing to the point that a gap opens up between the layshaft spacers and the gears. As long as this does not happen, the assembly behaves as though the shaft is of the diameter of the smallest spacer. We have calculated that 115 ft-lb on a MK9 layshaft (1"od) using a standard intergear spacer, provides the tensile force necessary to prevent excess flex up to about 160-170 ft-lb engine torque.

Beyond that we recommend going to MK5 gears and the 1.125" MK5 layshaft. Excessive shaft flexing encourages gear tooth failure.

When blueprinting a gearbox, we grind the end of the shaft nuts so that the gears align with 115 ft-lb of torque

Craig

[J Leonard]

Print Craigs post,frame it,hang it in your shop and remember where it came from.

[Bob Coury]

There has been a few threads where others mention that it is nice to have several nuts available with different thickness. These nuts look like they are in the 70 buck range each. Has anybody used standard off the shelf nuts to tried the hardened shim idea?

Thanks
Bob

[Nardi]

Can't you sand your nut down in thickness? Belt ssnder or flat surface and sand paper. It doesn't take much effort.

[Bob Coury]

I tried a few years ago, and did not get very far. And I was concerned about flatness even though I was on a surface plate. By my calcs, I should only have to remove about .005, so I think I am just going to purchase 7/8" ID shims from McMaster.

[Brian]

Shims that thin can easily crush out, and it's not very good engineering practice to use them in an application like this. If you need to go with shims in a high load application like this, the correct way to do it is to get a selection of shims that are around .100" thick and vary by a few thou. up and down. You should easily be able to sand .005" off your nut, I've done it with 120 grit paper in a few minutes, or just do it the old fashioned way - use a file... Won't take long.

Brian

[Steve Demeter]

Just be careful to keep the bearing surface of the nut square to the hole that the shaft runs in or you could have all sorts of other troubles.

For 27 years I used the 120 FT-LB then move the nut forward or back to the nearest cotter pin slot.

Never ever had a failure of any sort.

[chrisw52]

Just be careful to keep the bearing surface of the nut square to the hole that the shaft runs in or you could have all sorts of other troubles.

For 27 years I used the 120 FT-LB then move the nut forward or back to the nearest cotter pin slot.

Never ever had a failure of any sort.

This is what Porter racing told me. Once you get a good amount of torque on the nut to where it's close to a cotter pin slot, then you are very close to the proper torque.

[swiftdrivr]

I have heard that different gear stacks require different nuts due to the size of the gears being different, and told to have several nuts machined to slightly different thicknesses. My problem is that the holes don't line up at any point, for any track's gearset. As I have been experiencing cotter-pin failures, I am switching to a double nut setup. The advice I got was to have the nut's machined surface rest on the bearing race, so the nut marked with a "P" in the pictures is now turned around and put on first. I was advised to torgue the first nut to 80 ft/lb, then the jam nut to 115. We will see if that works. It certainly is easier than shaving cotter-pins to fit, or carrying several different nuts. [As for the bottom shaft, I go whichever way is closest, but tend to go tighter whenever possible.

[Steve Demeter]

I would highly recommend properly applied blue Loctite to said nut,.

That is what I have been told by people who know lots more than I do to use on the same nuts on a Staffs, which has no cotter pin holes. It USUALLY keeps them tight for 2-3 weekends.