"Test Mule" '74 850 Monoshock build

grandpaul · Oct 9, 2009

It seems like every time I think I've gotten rid of all my leftover Norton stuff, another deal comes along and I end up building another bike!

After building a rolling project bike and selling it, I had planned on selling off most of the leftover stuff I had in the "For Sale" section of the forum ( http://www.accessnorton.com/monoshock-750-commando-for-sale-t4761.html ); then I swung a trade for a complete '74 850 engine in great shape, in exchange for a Bonneville gas tank, head, set of pipes & set of pistons; pretty even trade at about a grand.

As I'm in the process of building a monoshock / inverted fork Mark III for a client, I figured what the heck, I can use that donor disc brake front end, I've got a spare swingarm, so I'll turn this one into a monoshocker. This will allow me to "de-bug" my prototype monoshock swingarm design using two standard Norton swingarms, and fine-tune the design and handling before building the client's swingarm to match.

Starting with a pile o' parts-

None of the engine parts in this photo will be used after all, nor will the Gas tank, seat, Ceriani forks and Arces yokes.

....hmmmmmmm...

Basically, just the frame, tranny cradle, swingarm, headers, rear hub, rear fender, oil tank, and clip-ons.

grandpaul · Oct 9, 2009

Here's the engine-

Mocked-up tack-welded prototype swingarm and rising-rate monoshock linkage-

grandpaul · Oct 9, 2009

All the rear end hardware fitted up in preliminary form-

Two issues:

1. I need a different shock unit with a bit longer travel full stroke,

2. I'll need to notch the upper shock mount arm to clear the chain-

Already studied this, and it won't be an issue notching the tube and welding in a section of angle iron to stiffen that section.

grandpaul · Oct 23, 2009

Well, it all came out rather nice. The length of the rising rate link plates is such that I can have 3 or maybe 4 different settings for the bottom shock mount, and the top shock mount will have at least 2 settings; that way, I can accommodate several different length shocks.

It feels pretty good, and the angles are just right where I have it at the moment. Good amount of rear wheel travel, and the shock is on it's softest setting.

Cut-out for the chain worked just fine, it's "extra beefy" there now.

Also got in a brand new set of stainless steel adjustable isolastics; these don't require modification of the pre-Mark III front mount, so less hassle. They were also less expensive than OEM, what a deal!

grandpaul · Nov 2, 2009

Thanx to Mike Gray on this forum, we worked a deal where the 74 monoshocker will have this tank on it:

I talked Kenny Dreer into scouring his storage shelves, and he found one last "boat tail" solo seat, so it'll also have this on it:

It's all coming together to look SIMILAR to this Dreer VR880 (not sure whose bike it is, but I like it):

(If anyone knows the owner, I'd like to have a chat with them)

This one will be monoshock, of course, and (for now) single front disc with hub rear brakes. Also, I'm not going to mirror-polish the tank, and will paint the seat & sidecovers Silver (no pinstripes).

RennieK · Nov 2, 2009

That must be the fastest way to remove the motor/tranny in situ

RennieK · Nov 2, 2009

The tank and boat piece tail are a natural, This is one Cool Mule!

grandpaul · Nov 2, 2009

Yep, the old "blue-tipped wrench", also called "smoke wrench" down south...

MichaelB · Nov 2, 2009

Looking good.
Have you worked out the air cleaner and inner rear fender?

grandpaul · Nov 2, 2009

There's no problem running a K&N with the Amal 930s.

Inner fender is a "field fabricated" item, specific to each bike, starting with a stock unit.

grandpaul · Nov 2, 2009

Time to get to work on the engine, starting with pulling the covers that will go to polish.

Tranny cover "before"-

Chucked the lump in the vice...

As was to be expected, the typical yukky oil with a bit of sludge (less than typical)

grandpaul · Nov 2, 2009

Pulling off the points plate, I noticed that one set of points happened to seem "wiggly"; the spring post popped off the plate when I removed it, it had been broken, but held "mosty" in place by the wiring and close quarters more on this very important discovery later)-

The engine's interior looks fairly clean; thankfully, no black coat of burnt-on oil-

Popped off the head after finding a bodged lower rear retaining nut with slots cut in it to tighten it by tapping a screwdriver with a hammer (previous mechanic must not have had thin-wall Whitworth wrenches). HMMMMMMMMMM.... One cylinder obviously not running like the other-

grandpaul · Nov 2, 2009

This is starting to make sense. The broken points plate may have been the reason this bike was "given up on"; it had caused the bike o be running on one cylinder!

Better, it looks like the engine had a fresh set of .020 pistons installed in clean bores, and peering down the intake & exhaust ports reveal very nice, clean, new valves!

So, I'm going to forgo opening up the bottom end. Actually, the only reason I even pulled off the top end was to strip the paint from the poorly painted cylinder head. This mill should be very happy with the slightly used Boyer electronic ignition I had sitting on the shelf for some time now. Other than polishing the engine covers, and putting it all toegether with a few new gaskets, that's all this thing needs to go back into the powdercoated chassis when it comes back next week.

Cookie · Nov 3, 2009

That's an interesting find. not sure I still would not want to look at the bottom end though, like at least pull the barrels and look in.

grandpaul · Nov 3, 2009

Now I know how Jerry Lee Lewis felt - "I couldn't sleep at all last night"

I just HAD to split those cases and have a look at the sludge trap, main bearings and rod bearing shells, or I'd never feel comfortable with myself.

It was a good thing I did.

Starting with the fact that it didn't appear that the cases had ever been split, and there were a few unnerving signs of possible issues including a chunk out of the front cylinder stud socket that may or may not have left stray chunks of aluminum floating around inside the cases (you can't tell but the cam lobes are in great shape)-

Not serious, but there was some surface rust on the flywheel-

Pistons looked okay, just a tad bit of scuffing, but they'll buff out-

grandpaul · Nov 3, 2009

Cylinders can stand a quick pass with a finish hone-

Cam followers typical, just a trace of flattening at the centerline, they'll re-grind easily-

Thankfully, nothing scary, just some sludge-

The left case half will get the weir lip milled out.

grandpaul · Nov 3, 2009

F.A.G. Superblend main bearings are in great shape, they'll stay right where they are-

Now we get down to the reason I'm MOST thankful I tore down the botom end - the big-end bearing shells had "given thier all", literally. The entire bearing face material was gone, right down to the copper cores-

The good thing is, good bearings in clean oil can go away without trashing the crank, if you don't go TOO far-

grandpaul · Nov 3, 2009

Hmmmmmmm..... somebody at the factory forgot to set the locktabs on the crank nuts-

YEEF! The worst sludge trap I've ever seen on a Norton-

grandpaul · Nov 3, 2009

Unbelievable-

One hellacious lump of grunt!

I could feel all the bearing material in there; good thing I went on in...

So, what started out as removal of the head to strip the paint, turned into a total overhaul, minus new pistons & valves.

swooshdave · Nov 3, 2009

Do you really need to hone? It seemed there are two camps (aren't there always two?) on when to hone. I can't recall the circumstances around when to or when not to.

"Test Mule" '74 850 Monoshock build

"Sons of Arthritus"