920 engine build waffle (2016)

Talking of the JS pistons and rods...

I’ll be using JS long rods and lightweight pistons again in the 920.

I want to keep a tight squish band clearence, after all, it’s slightly bigger on the 920 bore and I don’t wanna waste it!

Considering I’ll have a somewhat stiffer bottom end, and steel rods don’t stretch or expand much, whereas alloy barrels probably will expand, I’m gonna aim for .030” squish.

I asked Jim to thicken the crowns and put a .040” dish in them so that hopefully I can keep the squish at .030” but have a C.R. lower than 11:1. I’m aiming for around 10.5:1 ideally (same as I have on the current 850 motor).

Just gotta decide whether or not I’m gonna get the pistons Diamondize treated again. I have had the bores silicone carbide treated, I’m thinking the hard anodising would compliment that well. Trouble is I’ve become less and less of a fan of fancy internal coatings, so we’ll see...

If you don't mind sending them to Michigan USA - have them coated with slick plus at line2line, .001" thickness on each skirt. They won't scuff - even with the tighter clearance and the coating stays on.

Just when you’d forgotten all about this build boys...

I learnt from doing the back to back testing of the Comnoz RH10, on my 850 motor, just how important the head work is to performance. Even though that head was specifically a ‘street tune’ it still yielded a 9bhp increase along with huge mid range gains. All very impressive I thought.

But, my objective for the 920 motor has morphed into a much more simple philosophical one... more power...!

And before anyone chimes in about losing torque below 3,000 rpm, or killing the ‘gas mileage’ or any other such stuff... I know... I just don’t give a damn!

The other aspect that’s changed is that on the 850, despite (or because of) my newness to Commandos, I wanted to experiment and mix n match ideas. That’s a very time consuming process however, so this time I decided to simply stand on the shoulders of those who have done so before!

I got talking to Steve Maney about stuff, I tried one of his pipes previously and it gave big benefits, then, with some modifications to cam duration, the gains didn’t materialise. It made me realise that whilst his pipe is a fabulous design, it’s only capable of its best within specific parameters of cam / head / pipe relationships. It’s all designed to operate as a package.

So... long story short... I decided to go for that package.

As my objective was now simpler (more power please, f*ck the rest) it was a straightforward decision to choose his stage 3 head. This has 5mm OS inlet and 3mm OS exhaust valves. The porting is exquisite, the inlets are matched to 36mm manifolds. I have 35mm and 39mm FCRs to choose from, I might start out with the 35s as they’re a known quantity and experiment with the 39s afterwards, Steve favoured the idea of 39s. So do I !

The eagle eyed amongst you may notice the stainless steel inserts for the head bolts. Also, the external oil drain, this is made necessary as the inlet ports at this size break into the internal drain. It’s a shame in a way as it now needs an extra external pipe, but at least it’s one potential head gasket oil leak cause eliminated!

The only downside to the head is it’s fresh blasted finish look horrid next the the tumble polish barrels and cases, so my next job is to send the head off for tumble cleaning.

The timing case internals are all on their way from Andover Norton along with a heavy duty IWIS camchain from Jason (the new chain man), and I’ll be putting a Comnoz auto cam chain adjuster in there too.

So, at least a couple of steps forward! I’m still aiming to get the 920 lump in by next spring. But I’ve said that before!

Some ‘head shots’ for y’all below...

Schweeet!! Very nice photos Nigel, and thanks for posting your updated plan of action.... I for one am jealous !!!

Nigel,
WOW, nice stuff. Knowing very little about Maney products I have a question. Is that you old head that’s been reworked again or is that head supplied by Steve and if so what RH is it. Good luck with your build and hope to see it on the road in the spring.
Pete

Nigel,
Looks great, all up to your usual standard.
Check this out, don't know what your projected budget for the build is but this might be cheaper (yes, I know how much a special costs to do !!!)
ebay number 323549490833
Knowing you, you've probably seen it anyway, it looks fab !
sam

Sam,
Yes I’ve seen that, and I’ve spoken to him (Dan) before. Whilst that’s a large chunk of wedge, it’s actually a very good price for the quality it is.

I nearly bought a chassis from him so I could build another bike around my 920 but (fortunately) after trying some Seeley’s for size, I’m just to big for one.

So I’m sticking with the plan of putting the 920 in The Trident Hunter. I’ve actually been very happy with the Commando frame, for my riding standards at least, and, of course, I like the idea of keeping the isolastics.

Of course, the advantage to putting something together piece by piece over time, is it naturally spreads the cost. And the missus doesn’t really notice what I’m doing!

Pete,
The head ‘core’ was supplied by Steve, it actually started life as a 750 head. I decided to do it this way so that I can really ‘go for it’ with the 920 engine spec and Keep the 850 motor whole, which is a peach, to fall back on.

Looking at the machining of the fines for the oil drain, I'm reminded of Ludwigs' modification to the fines between the push rod tunnels in front.
He drilled a hole through them to allow air movement from the dead air space. I believe he measured the improved cooling, but I'm just going on my memory.

franko said:

Looking at the machining of the fines for the oil drain, I'm reminded of Ludwigs' modification to the fines between the push rod tunnels in front.
He drilled a hole through them to allow air movement from the dead air space. I believe he measured the improved cooling, but I'm just going on my memory.

Click to expand...

Indeed he did. I did that on my 850s head and will do it on this one too. I didn’t measure the difference, but the logic made perfect sense to me.

Has anyone tried a graphited gasket that can accommodate the inevitable creep between an aluminium head and an Iron barrel?, This type of material is used on my 1930's bike in a similar situation.

norton bob said:

Has anyone tried a graphited gasket that can accommodate the inevitable creep between an aluminium head and an Iron barrel?, This type of material is used on my 1930's bike in a similar situation.

Click to expand...

You’ll get a better response asking this in a new thread. This thread is about my 920 build which uses alloy barrels, so kinda irrelevant really.

As mentioned gents, I have 35mm and 39mm FCRs ‘in stock’ to choose from on the 920.

Given the fact it is intended as a max power motor, and it has 36mm ports, and it’s good practice to have a bigger carb than port (notwithstanding the debate ref blending / taper / radius) then it seems to point to the 39s being the best option.

Has anyone on here got any experience in using 39mm FCRs on a Norton?

Not directly applicable but I had a Ducati M900 to which a previous owner had fitted 39mm FCR's along with race exhaust, so sounds appropriate for the engine size and power plans.

Thats kinda reassuring Iain, thanks for that. Actually the 39s I have were bought from Kenny Dreer and were destined for his original version of the 961.

So, on balance, I think they should be good.

Ok, thread revival time folks...

So, I says to the Missus “nah it’s not a big job love, just whip the old engine and box out one pop the new ones in”.

Fortunately, she knows me well enough to tell when I’m talking utter bollox!

I took the cradle out as it’s easier to grind it in order to fit the TTI box, and because I wanted to grind off the powder coating from key mounting point faces.

Stroll on... I was kinda dreading the ‘TTI cradle fit’ day, and as it turns out, with good reason!

Many thanks to those who offered prior advice regarding where to grind the cradle, you were right. I guess I was hoping that Bruce and Co might have taken some of the feedback on board and, well, made it fit. Alas not.

I got there in the end though, and touched up the frame and cradle where needed with the thinnest whif of ‘rattle can’ gloss black.

Hopefully tomorrow I can get the cradle back in, TTI fitted, back wheel back in, etc.

Cases are with my machinist at present, hopefully I’ll have them back soon and can start engine assembly...


This was a shinny and well running bike a couple of weeks ago...

franko said:

Looking at the machining of the fines for the oil drain, I'm reminded of Ludwigs' modification to the fines between the push rod tunnels in front.
He drilled a hole through them to allow air movement from the dead air space. I believe he measured the improved cooling, but I'm just going on my memory.

Click to expand...

I've seen this modification mentioned a few times, but cannot find any additional info, can anyone point me in the right direction?

acadian said:

I've seen this modification mentioned a few times, but cannot find any additional info, can anyone point me in the right direction?

Click to expand...

Post #19 here..

https://www.accessnorton.com/NortonCommando/increasing-oil-flow-to-head.26731/


Cheers,

cliffa.

Hey Nigel! I just realised your wife and I have something in common.

https://www.accessnorton.com/NortonCommando/increasing-oil-flow-to-head.26731/#post-400885

https://www.accessnorton.com/NortonCommando/increasing-oil-flow-to-head.26731/page-2#post-400926

cliffa said:

Post #19 here..

https://www.accessnorton.com/NortonCommando/increasing-oil-flow-to-head.26731/


Cheers,

cliffa.

Click to expand...

Well, some progress at least, this might only look like a gearbox in a frame to you, but to me it marks the end of a right PITA of a job !

Just waiting on some bits arriving and the back wheel can go in.