Britbike forum Forums British Motorcycle specific Brands Norton bulletin board Norton Top End Job coming up ....

Bit late to say that - with the head sitting on the bench there ?!

Worn motors can often react poorly with all their accumulated carbon removed. ?
Out of the frying pan, into the fire ?

You wouldn't really expect a sticky valve these days, unless new guides have been fitted recently,
and they are a bit tight. ? Loose and worn is more likely, with lottsa miles under the belt.
Bit lean and popping is a common condition with this.

You'll soon know, with the valves out for a look.
I'd expect that one is a shade burnt, or has a poor seat condition.. (?).

Well the comment was directed at Hugh and as far as I know he hasn’t removed the head yet. If carbon is what holds his engine together, then he’s pretty much screwed anyway.

Ah, I must have missed that thread-jacking.

Carbon is what keeps many old motors going - strongly even ?

I can recall a lad down the street tipped a can of that potion into his old Ford.
When I arrived, that end of the street was enveloped in a smoke cloud !
I caught up with him some time later. he said his engine required a full rebuild
after that - much of the compression was gone, it smoked something terrible,
and there were little chunks of carbon everywhere - inside and out.

I have heard of folks spraying water into running engines, and it seems to steam clean them, inside ?
Some aero engines did this as normal running, so the jury is well and truly convinced ?
Possibly for different reasons though ...

Cerium oxide nano particles at 5ppm in fuel acts as a catalyst to lower the temp carbon/soot burn off will do the trick. Used in Diesel Particulate Filter cleaners so the DPF gets cleaned at normal exhaust temps without the need for a regen.

This is just a simple question so I don't break something, doing something I've never done before but only read about.

Do the MkIII Commando rocker spindles just come out with a slide hammer? Just so happens that the auto-advance puller slide hammer for the BSA fits the threads in the end of the rocker spindles, and the manual shows them being pulled out with a slide hammer, so I went and hammered for a bit and nothing.

Do I need to heat the head for a bit for them to loosen up? Or is something else in the way? I've read the Access Norton threads on the orientation of the spindles when I put them back in, so I think I've figured that out, although I'll need to figure out what kind of shims and spring washers are going to fall out as I pull the spindle ....

Lannis

Some rocker spindles have come loose with age, but they are supposed to be tight, and require the head to be heated prior to removing them.
Also, check the manual to determine the correct orientation for the flats on the spindles prior to reassembly.
... Gregg

Thanks! I have a heat gun and an infrared thermometer so I'll tackle it in the morning. Once the spindles are out I'll take out the valves and see what has to be done. I suspect that all the valves except the near-side exhaust valve that was leaking under the leak-down test will just need to be lapped ... that exhaust valve will need something more, I'll bet.

Lannis

Cold extraction will quickly or eventually kill the fit of the rockers in the head. Unskilled owner work hides DPO damage and makes original "unrestored" bikes more valuable as a core.
An external heating only softens the grip on the outboard end.
My industrial oven heats the complete head through and through softening the grip on both ends.
No Magic answers, but as seen on the AN Commando forum even removing a simple dowel is not so simple after all....

it is advised to warm the head to remove the spindles there is a spring washer ( thackery washer) to the center of the head and a thin shim to the outside of the head..

Windy and Dave -

Thanks, you're right, nothing is simple on these things even though (as Windy says) they're no more complicated than working on a commercial lawnmower..

I don't have an industrial oven. I started trying to heat it with a 2000W heat gun but the heat radiates away faster than I can put it into it.

However, it can't get away from a fan-shaped MAPP torch flame used to heat the entire head as close as I could get it. I realized that the inboard end had to be heated too, so I gently played the torch over it, stopped to let it soak through, played the torch over it, and repeated until I had a pretty consistent 180 degF over the surface of the head according to the IR thermometer. I then used the (fairly light) auto-advance slide hammer to tap out the shafts; whatever mechanical sympathy I possess (and I don't claim much) tells me that I didn't scar up, upset, distort, or otherwise damage the spindle mounts considering the light, consistent taps I was giving it.....

Lannis

Lannis,
Having got that far, I would take off the cylinder and look at the cam lobes.

Ed from NJ

Getting ready to do just that! However, I am embarrassed to say that the manual says "Remove the five cylinder base studs and four through-bolts" and I see the 5 base studs but have no freaking idea what they mean by "through - bolts". I promised to do my research before I asked a stupid question so I'm off to do that.

Lannis

If you look at the cylinder in the vicinity of where the spark plugs were,
there are the tops of the 4 hex cap screws visible.
These are the through-bolts that were new for the 850.

Supposedly they were the cure for all the base studs pulling out of the 750 crankcase,
and yer cylinder/head lifting up and falling off !!! (well maybe not quite).
Seems to have worked though, 850's seem to be problem-free in this area.

The tops of these hex cap screws are somewhat obscured in your photo of the cylinder top by the head gasket.
Remove this, and all will be visible ....

Yep, I went to the parts diagram and found four socket-head bolts and came back determined to find them, and then realized that the head gasket was still in place. I'd never heard of a bike that had cylinder fixing bolts right in the sealing area of the head gasket, but I pried it off (it was stuck pretty good) and there they were.

Cylinder is still on, though ... I have another "I don't want to break anything" question that isn't answered anywhere except by experience. Took out the front 3 studs and the 4 through-bolts ... the rear 2 studs won't come off unless the cylinder is lifted a bit to allow those long nuts to clear the studs and cooling fins. But that cylinder is REALLY stuck to the cases ... the rear 2 studs are loosened as far as they'll go, but the cylinder is stuck there. Is it permissible to use the nuts to "jack" the cylinder off the case and break the seal so it will lift off? I gave a pretty good pull on the short 7/16" wrench I'm using, but the cylinder didn't lift at all.

What's the cool Commando "in-the-know" way to get the cylinder broken loose from the cases? There's nothing to beat on except fins, and I don't want to do that ...

Lannis

https://andover-norton.co.uk/en/shop-drawing/123/engine-cylinder-cylinder-head
Items 14 (x4)


Actually done to strengthen the barrel base.

New 750 barrels are now made with the same '850' through-bolt pattern casting.
https://www.britishmotorcycleparts.co.nz/06-1705-06-0396-cylinder-barrel-750-commando

While I'm trying to get the cylinder off the cases so that I can measure bores, pistons, and ring gaps (I hope to have that all done tomorrow), maybe we can have a look at the head.

RF's tool set included a valve spring compressor sized for Brit bike valves:



I learned a bit about good shop practice, studying under KarlB, who learned as an actual apprentice ... Bag 'em up!



The exhaust valve seats are just ugly. No wonder I didn't have much compression. Intake seats look grand, I can just lap them. But some smart guy is going to have to re-do the exhausts, I suspect.




How do I know if the fit of the valves in the guides is good? I had no valve-guide-type smoke or anything, and they feel nice and slick, but there's no spec in the manual that I can see. And what do we think happened to the exhaust valve seats? The valve lash was always good, matter of fact a little over the spec, so they weren't burned by being held open during the cycle ....

And the big question. This bike needs to be on the road in 40 days. Does the panel know of anyone who can renew these exhaust valve seats and lap the valves to them, in that time period? I'll get the head to whoever might can do it, if I have to drive it there, but it can't go into much of a work queue.

Pistons, rings, and cylinder tomorrow. Thanks for all the help and interest.

Lannis

I suggest you clean up the combustion chambers and Ex. valve seats so we might get a better idea.



Do they actually need replacing (can't tell from those pictures) or just a grind and maybe new valves (and springs)?

Yes you need to clean up the valves and seats, and have a good look.



That was already done once, early in the life of the 750.
Early 750 cylinders were quite thin.

That's a heavy carbon build up, either from fuel without modern additives or rich running most likely in the mid throttle range ie needle jet badly worn. The exhaust seats are likely good under the carbon.

And/or burnt oil.
In which case, the muffler internals should be in good condition. !

Whichever, it would have been a tad black or smokey or 'fumey' trailing along behind. ?

We didn't hear the washup of the valve guide seals on the inlet guides. ?
If they've come unseated, that alone could account for a bit of oil burning.

Rings is another possibility, driveside rings wear faster than the timing side normally due to oil flow out of crank favouring the timing side.

Of course.
Its a long trip from top to bottom, plenty of potential to wear.

There is discussion places of the merits of 3 piece oil rings v's one piece ?

All -

Thanks for your help to date - all good advice.

I don't think I'm going to need to send this head out anywhere. Cleaned it up ....





as suggested, and the valve seats look very good, no erosion, burning, etc. - it was all carbon. And the valve sealing surfaces themselves look good.

The valves are a nice sliding fit in the guides with no wobbles. The valve oil seals are uncracked and flexible. How are the oil seals fitted into the head? Is it best to leave them alone (on the "never wake a sleeping baby" principle) or replace them while I'm in here? My plan is to hand-lap the valves back to the seats and let 'er rip.

A note - I didn't take the engine down because of oil consumption. The bike never smoked, and didn't use any oil even on a long trip. I'm not sure why the carbon buildup (perhaps it IS a fueling issue, although the carb needles are new, and the needle jets also, and besides that gauged with a go-no-go bore gauge that John Healy sent me after they were seated in place).

Next thing, though, is the pistons. I've carefully counted 9 Fasteners removed from the cylinder block (5 studs and 4 bolts), and that cylinder block will NOT move at all. I've lifted straight up, and pushed sideways, and shouted very loudly at it. Any suggestions that won't threaten the integrity of the cooling fins .... ?

Lannis

Refit the cylinder head with some (or all?) Fasteners, then...

The inlet valve seals fit over the top of the inlet guides, they could be the cause of the carbon even uncracked and flexible, so I would change them. I change them regardless every time I am in their but that was at least 40 years ago when i fitted new rings. Other than that it does look like a hand lap and reassemble job plus re-anneal the head gasket if its copper.