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920 engine build waffle

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920 engine build waffle

Postby Fast Eddie » Mon Oct 31, 2016 4:20 am

Ladies, I thought I’d do anther ‘engine build’ type thread for those nerds that are interested in such stuff. I thought I’d do it separately to my previous one and title it as a 920 build to help those searching around for 920 build info in future.

Well, my story is that I bought a Maney crank to put in the ‘Blue Bomber’. Then after a lot of thought, I basically decided that the best place to put such a nice crank would be in some nice strong Maney cases. Then, further thought deduced that such a strong bottom end justified some improvements with regards to output. And so, another 920 project was born!

So I got a set of cases from Steve Maney, machined to accommodate a standard primary case, this weakens them somewhat, but I really wanted to keep the stock primary case set up. It will still be plenty strong enough for my needs, according to Mr Maney.

At my request, the cases have no holes drilled from crank chamber to timing chest, this saves me having to plug them for using a Comnoz / cNw reed valve breather. Maney cases come machined to take the Combat style breather at the rear of the case, so I’ll use the cNw style breather that bolts directly into this location.

As mentioned previously, I already had a Steve Maney crank on the shelf that I bought earlier. I sent this back to Steve for him to fit the main bearings and shim up accordingly to the new cases. I know I could have done this myself, but being in ‘this deep’ already, I thought I’d let a specialist do it right! The cases have been machined to accept a set of Steve’s 920 barrels, which have been finish bored to 81mm in readiness for the JS pistons.

I have had extensive conversations with Jim Schmidt (thanks Jim) regarding pistons. I have used his high compression 850 pistons very happily hitherto in the Blue Bomber. We arrived at an 81mm 920 design based on the spec of the 850 high comp pistons, with extra material in the crown to allow for a 1mm dish machined into the crown. According to my ‘fag packet’ calculations, this should allow a tight squish and keep the CR at a reasonable 10.5:1 (or there about). I’m aiming for a 030”-.035” squish clearance, which is what I am currently running with no sign of any contact anywhere. The pistons will be hard anodised with the ‘Diamondyze’ process as per my current 850 pistons.

The fabulous Comnoz ported RH10 head will be used as is, apart from opening up the squish area to suit the 81mm bore.

I really like the BSA cam followers that I am currently using with my JS1 cam kit, but the flat lined peak BHP graph that I had on the dyno (virtually flat from 6300 to 7500) led me to conclude that a hotter cam might help liberate some power above 6300, plus the increased displacement will have increased breathing requirements, so, after much deliberation, I have opted for a slightly hotter JS2 cam. The JS2 has the same duration as the JS1, but has more lift, and is very similar to the PW3. I will be using a Webcam hard welded JS2 ‘smoothramp’ version. Actually ‘Brooking850’ has a large part of the blame here as his glowing praise for the JS2 cam in his race bike certainly helped to persuade me in that direction!

Its not likely to be a very quick build, I am aiming to fiddle around collecting the necessary parts (and spread the cost) and hopefully will get the engine built and nailed in to the frame next winter (2017-2018).

I’ll post some pics of various bits n bobs soon.
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Re: 920 engine build waffle

Postby lynxnsu » Mon Oct 31, 2016 4:37 am

nice
like your down to earth info , no bullsh......
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Re: 920 engine build waffle

Postby grandpaul » Mon Oct 31, 2016 6:08 am

This should be fun.

Why not move it to the "Projects" section?

Oh yeah, pix, please...
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Re: 920 engine build waffle

Postby cjandme » Mon Oct 31, 2016 8:19 am

All I can say is Awesome! I look forward to any and all progress that you might share with the rest of us here on these threads. :mrgreen:
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Re: 920 engine build waffle

Postby trident sam » Mon Oct 31, 2016 9:02 am

Sounds like a plan mate !
I look forward to seeing you in the Trident's rear view mirrors :twisted:
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Re: 920 engine build waffle

Postby BritTwit » Mon Oct 31, 2016 9:42 am

trident sam wrote:I look forward to seeing you in the Trident's rear view mirrors :twisted:
sam


Nigel now I'm a fan of your 920 project too. :lol:

Keep us up to date.
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Re: 920 engine build waffle

Postby Fast Eddie » Mon Oct 31, 2016 10:10 am

trident sam wrote:Sounds like a plan mate !
I look forward to seeing you in the Trident's rear view mirrors :twisted:
sam


Where dya get the mirrors that can see through smoke clouds Sam...?
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Re: 920 engine build waffle

Postby trident sam » Mon Oct 31, 2016 10:30 am

Fast Eddie wrote:
trident sam wrote:Sounds like a plan mate !
I look forward to seeing you in the Trident's rear view mirrors :twisted:
sam


Where dya get the mirrors that can see through smoke clouds Sam...?


Smoke Sir,.... :roll:
I'll inform Neil of your insult my man.
Now just get it built, don't worry I'll let you catch up now and again, makes it more fun . :lol:

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Re: 920 engine build waffle

Postby acotrel » Mon Oct 31, 2016 11:16 am

When you go to that big bore size, how do you seal the bit between the cylinders at the centre of the head, from leaking compression ?
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Re: 920 engine build waffle

Postby gortnipper » Mon Oct 31, 2016 1:10 pm

Fast Eddie wrote:The fabulous Comnoz ported RH10 head will be used as is, apart from opening up the squish area to suit the 81mm bore.


Well, based on our PMs, you know that I think this is a mistake. Or are you going to use the FA head on you primary motor? :mrgreen:
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Re: 920 engine build waffle

Postby worntorn » Mon Oct 31, 2016 2:15 pm

Nigel, will you use the stock transmission with this 920?
If you add it all up, it sounds like a lot of power will be running thru the box with this new motor.
I know Jim Comstock is doing something similar with his bike and it has kept it in one piece by exercising restraint.

With all of these Tridents gunning for you, it seems you might need to go a bit harder on the power train.
I see a TTI box showing up soon.

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Re: 920 engine build waffle

Postby Fast Eddie » Mon Oct 31, 2016 3:23 pm

worntorn wrote:Nigel, will you use the stock transmission with this 920?
If you add it all up, it sounds like a lot of power will be running thru the box with this new motor.
I know Jim Comstock is doing something similar with his bike and it has kept it in one piece by exercising restraint.

With all of these Tridents gunning for you, it seems you might need to go a bit harder on the power train.
I see a TTI box showing up soon.

Glen


It would be nice Glen, as would the FA head that Gortnipper suggests. Sadly though, those two items would probably double the budget, so I'll have to manage without.

I will swap my belt drive from Norvil to Maney, which speeds up the primary gearing and eases the loads on the gearbox and will probably fit a Maney outrigger. Both of these items are already 'on the shelf' and I'm already using a strengthened AN gearbox shell.

So I think my direction here has already been set.
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Re: 920 engine build waffle

Postby Fast Eddie » Tue Nov 01, 2016 12:52 am

acotrel wrote:When you go to that big bore size, how do you seal the bit between the cylinders at the centre of the head, from leaking compression ?


Well, hopefully, with a head gasket.
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Re: 920 engine build waffle

Postby Matchless » Tue Nov 01, 2016 6:16 am

On the subject of head gaskets, I wonder if Jim Comstock is any closer to having Cometic 920 head gaskets made. If he doesn't read this I'll send him a PM.

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Re: 920 engine build waffle

Postby worntorn » Tue Nov 01, 2016 8:02 am

Anyone can send a pattern gasket to Cometic for reproduction in one of their chosen types.
The cost is pretty low, if I remember correctly.

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