Return of the Nitrous Norton (2016)

Time to start getting the bike ready for the Bonneville Motorcycle speed trials in about 4 weeks! Last ran in 2014, with some info here

https://www.accessnorton.com/NortonCommando/norton-ready-for-bonneville-speed-trials.17348/

And engine teardown details here

https://www.accessnorton.com/NortonCommando/920-race-engine-teardown.17644/

I stripped the bike completely because of the corrosion problems with running on the salt. Mostly the rolling chassis just needs reassesmbly. This is the frame, just needing a little paint touchup



And these are all the parts for the rolling chassis, except for bodywork and tank, and the nitrous bits.



This is the Nourish crankshaft and the new cases. The crank is MK3 dimensions, and the new cases are made up of a stock MK3 timing side with a Maney drive side. Steve did these cases for me back before he was making both halves. He started out just making the drive half and mating it to stock timing halves. I've had it for a long time, and finally have a good use for it.



This is my setup for boring out the case mouths to take the 920 cylinders.



While it was in the mill, I also converted the four through bolt threads to Timeserts.



And finally, the frame with a little paint touch-up.



That's it for now. Hopefully I'll be making rapid progress on this one.

Ken

Beautiful. I am only a little envious my Featherbed frame is lacking such esoteric enhancements.

Slick

The bike was originally a vintage road race bike, and I kind of got carried away with drilling the lightening holes. The swing arm was from Mick Hemmings, a long time ago. There is a square section reinforcement on the lower rear cross tube that I put in after the frame broke in that area. It's also been reinforced with thick washers at the swing arm pivot after it wallowed out the original holes. There was already an added tube brace from the front upper cross tube to the steering head when I bought the bike back in 1984. I also added some simple brackets for the rear-set foot controls, and a new cross piece to the rear section for seat support. Other than that, it is all original :lol:

Ken

Ken - thanks for posting the pics, I'll be watching.

If you need a guy to stand around who thinks he's not in the way but somehow helping . . . . . I'd love to come out to see you and your grandson again.

Thanks for the info on the frame details. The enhancement to the frame I was most envious of is the engine enhancement.

Slick

PS: good luck with the run on the salt.

xbacksideslider said:

Ken - thanks for posting the pics, I'll be watching.

If you need a guy to stand around who thinks he's not in the way but somehow helping . . . . . I'd love to come out to see you and your grandson again.

Click to expand...

Any time, John. Just give me a call to be sure I'm here.

Ken

texasSlick said:

Thanks for the info on the frame details. The enhancement to the frame I was most envious of is the engine enhancement.

Slick

PS: good luck with the run on the salt.

Click to expand...

There is that, too. I vintage raced the bike for quite a while with AHRMA with a standard 750 built to Axtell specs, then put a short stroke 750 in it for Bonneville runs and got some records, none of which lasted very long, and then in 2014 went to the 920 on nitrous. If I can get a few good runs, I'll return the bike back to a street legal café bike, like it was when I bought it.

Ken

Hey Ken,
Its been two or three days since we talked. I am sure that this is a roller by now.

Son of Siredward said:

Hey Ken,
Its been two or three days since we talked. I am sure that this is a roller by now.

Click to expand...

I wish! Still working on the motorhome engine instead.

Anyhow, I still have almost three weeks left. No need to rush, right?

Ken

Motorhome repaired, back to Norton building. The old cast pistons collapsed the top ring land in the 2014 meet, so I'm fitting a new set of JE pistons. The old bores were slightly undersize to fit the old pistons, so I had to hone them out several thousandths to get the .006" clearance for the new ones. I'm hoping that's a good choice with the nitrous. The cross hatching is much better than it looks in the picture. Something to do with using the flash, I think. I honed them out to .005" with 150 grit stones, then to .006" with 280 grit, and finally a bottle brush hone to knock down the plateaus. I still have to clean everything up and touch up the black paint, but the hard bit is finished. Next step is machining the piston domes for high compression and proper squish clearance. I have the pistons made deliberately taller than stock for more compression, but in this case, since the head and cylinder have already been skimmed years ago for higher CR, I need to reduce the deck height a significant amount just to clear the head. I will still have a much taller top land than with the previous pistons, so not much risk of collapsing the top groove.



Ken

lcrken said:

Son of Siredward said:

Hey Ken,
Its been two or three days since we talked. I am sure that this is a roller by now.

Click to expand...

I wish! Still working on the motorhome engine instead.

Anyhow, I still have almost three weeks left. No need to rush, right?

Ken

Click to expand...

You are just fine.
As of this morning you now have two weeks to have it in the trailer behind the motorhome heading to Bonneville.
By the end of the weekend you should have the motor complete and in the frame.

I am pulling for you!

Change of plans. I built the original 920 engine a long time back, and a couple of things had slipped my memory. At the time, I was going for high compression with as light a piston as I could get. I ended up with a cast flat top piston from Fair Spares (from a Ford 2000, I think). To get the CR, I machined the top for a bit of dome, taking the top land down to .150" in the process (which also explains why it pinched the top ring on nitrous), and milled .065" off the cylinder. The head I used, an ex-factory big valve race head, had already been milled significantly, probably .040" or so. That worked fine with the cast piston, but it now looks like I can't make it work with my forged JE pistons. I would have to take .205" off the top of the piston, and re-cut the valve reliefs to get it to work with the .040" copper head gasket, and the deck isn't thick enough for that. I can't see trying to use two head gaskets and a spacer plate for an engine running nitrous. To make it work, I need to either order some custom pistons, or sleeve another cylinder out to 920 and still use a thicker head gasket and a copper base spacer. Not happening in time for Bonneville.

Plan B: Put together an ultra short stroke 750 from scratch. I've had the bits from Steve Maney for years to build this engine, but never managed to get to it. This looks like a good time. It's a 75 mm stroke and 79.5 mm bore combination. It includes a shortened alloy cylinder and a Stage 3 big valve head. This is the bits laid out on the bench.



The cases have a Maney drive side and a stock timing side. I'm using a C3 bearing on the drive side and a C1 on the timing side, because the fit in the stock case is not as tight as in the Maney. I've already checked for end play, and am about to fit the .010" shim shown in the picture into the drive side. That will give me .006" end play cold, and a bit more when hot.

I've just checked the crank to see what the balance factor will be with the steel rods and JE pistons I'm planning to use. I'm hoping it will be close enough that I don't have to machine the crank to add or remove weight, but haven't done the calcs yet. This is the crank on my static balancing stand.



I doubt if I can get it all together in time for the Bonneville meet that starts a week from tomorrow, but I'm going ahead anyhow. If it isn't ready for that, I should at least have it done in time to do a couple of meets before the end of the year here at the El Mirage dry lake.

Ken

Nice stuff, Ken.

Isn't it a hoot to have stashes of cool parts that you can just any day of the week decide you want to play with?

"I know the feeling" (although your stuff seems to be an order of magnitude cooler)

By golly, you just gave me the bug to FINALLY put together my VR880 engine & tranny...

Ken, I want to come and look under your workbench one day if that's the kind of stuff you find lying around the place!!

A decade or two back, when I was still actively involved in road racing, and had good cash flow from a decent job, I accumulated a lot of cool stuff that I planned to eventually use to build all sorts of interesting Norton projects. Most of them never became reality, and now that I'm retired and on a more limited income, I'm trying to finish some of those projects and use up some of the bits. In theory, I now have the time to do so. In reality, it doesn't seem to work out that way. Being 74 years old and having some family obligations might have something to do with it. I'm starting to realize that I've still got too many potential projects to finish before I get really feeble, so I'm trying to find time to sort through the accumulation and start selling some of it. Trouble is, it's way more fun to work on projects than it is to sort and prep stuff to sell.

Ken

So, finally back to building the 750 engine again. I had to add a couple of 3/4" plugs of heavy metal to the crankshaft cheeks to bring the balance factor up to 62%, to make up for using steel rods instead of aluminum. This is the 75 mm stroke Maney crank with a pair of Don's (madass) steel rods.



This is the Megacycle N480 cam and BSA lifters I am using. This engine is for maximum top end power for Bonneville, so I'm using the longest duration, highest lift cam I have.



I'm using a stock 850 timing side case half mated to a Maney drive side half. I expected to have to open up the cam tunnel in the stock side, and I did.



What surprised me was that I also had to open up the tunnel in the Maney case, but only very little. This is one of Steve's early case halves, and I suspect that the later ones have a little more clearance there. Steve experimented with the N480 cam at one time, so I'm sure he's aware of how much room it needs.

It's pretty straight assembly from here until I get to fitting the pistons. I expect to be machining the heads on my JE pistons to get a higher compression ratio, as well as making sure I have enough valve-to-piston clearance. I will probably also have an issue with valve-to-valve clearance, but can probably sort that by sinking the exhaust seats a bit. I'm also going to have to make some shorter push rods to suit the short cylinder. Stay tuned for a report on whatever unexpected issue shows up next.

Ken

Thanks Ken. Good pics. Square cam lobes are always a "tell."

xbacksideslider said:

Thanks Ken. Good pics. Square cam lobes are always a "tell."

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Hi John. They are pretty lumpy, aren't they? I'm pretty sure the regular RD springs I've been using for so many years will not be up to it. I'm expecting to need to run it to at least 8000 rpm, and maybe 8500 rpm, to get max horsepower, and I'll be looking for a better spring package. At the moment, the options look like beehive, conical, or just some stronger conventional coils. RD has an IRL spring set that will fit that I think might work.

Ken

Glad your "vacation" is over, and this project is back on.

I think I see a kenc vs dynodave showdown in the making...

Got the bottom end together today, and mocked up the cylinder and piston to check compression ratio and squish clearance. The in-modified JE 79.5 mm piston is .250" above the cylinder deck.



This is the piston after trimming the squish band area down by .140", leaving a beveled dome for higher CR.



I cc'd the head, and calculated the CR with the modified piston to be just over 12:1. I expect to now have to cut the valve notches deeper, so will lose a small amount there, but it should still be pretty close to 12:1, and that should be enough. At this point it's getting more difficult to raise the CR any higher, and the return for doing so is diminishing. I do plan to run it in the gas class first, and it should be fine on high octane race gas.

Next step is to sort out the valve train.

Ken