Anyone as experience with 920 engine?

Fast Eddie · Sep 20, 2017

SteveA said:
lcrken said:

Unless he's changed them since I bought mine, Steve's cylinders use different head bolts (3/8-16) and studs (longer). The cylinder through bolts are the same as stock Norton, unless you are getting shorter cylinders or one without two of the counterbores for the bolt heads).

Ken

Click to expand...

Right Ken, so basically the CNW ARP kit with waisted bolts cannot be used with Maney cylinders.

If you mean the cNw head bolts then no, Maney barrels use different head bolts with (I think) a metric thread.

ARP do do the correct bolts though, just not waisted.

I got some and got them waisted, all with the help of a forum member who I'm sure will chip in if he feels like doing it again !

jseng1 · Sep 20, 2017

SteveA said:
lcrken said:

Unless he's changed them since I bought mine, Steve's cylinders use different head bolts (3/8-16) and studs (longer). The cylinder through bolts are the same as stock Norton, unless you are getting shorter cylinders or one without two of the counterbores for the bolt heads).

Ken

Click to expand...

Right Ken, so basically the CNW ARP kit with waisted bolts cannot be used with Maney cylinders.

I've been making the fluted ARP bolts for the Maney cylinders. That's all I've made them for. I started with triangular 3 fluted bolts - then switched to 2 flutes cause they work just as well (same cross sectional area and strength). Its a lot of time and machine work - not my favorite project.

lcrken · Sep 21, 2017

Oops!

Sorry Steve, but I made a mistake on my post about Steve Maney's fasteners. His head bolts are Metric, not 3/8-16. In answering your question I went out to the shop and checked the fasteners on the 750 engine I'm currently building. But I lost track of the fact that I had fitted it with Timeserts and converted it to 3/8-16. I've edited the post to correct it. Sorry for the misinformation.

Ken

lcrken · Sep 24, 2017

Okay, so now I have to try to get this right on the third try. As Jim Schmidt pointed out to me, the head bolts in the Maney kits are not metric, but are in fact 3/8-16. I think I got them confused with the Robertson alloy cylinder kits I used to sell, which did use metric head bolts. Sorry about that. I really am getting less reliable in my old age. I did convert the cylinder in the 750 I'm building to Timeserts, but the 3/8-16 size was not a change from the original threads.

Time to edit my earlier post yet again.

Ken

Thruxton · Oct 1, 2017

I run a 920 engine in my race bike. It has mk3 cases bored to take the sleeved 850 cylinder with a Mick Hemmings big valve head. Denco lightened mk3 crank, carrillo rods, 4S cam. Rita ignition. Running 36mm smooth bore mk2 amals on long inlet manifolds. The compression ratio is low. The motor was built in the 1980's and has been raced since with no problems and usual maintenance. It has 58 rear wheel horsepower and 58 ftlb torque.

Fast Eddie · Oct 1, 2017

Thruxton said:
I run a 920 engine in my race bike. It has mk3 cases bored to take the sleeved 850 cylinder with a Mick Hemmings big valve head. Denco lightened mk3 crank, carrillo rods, 4S cam. Rita ignition. Running 36mm smooth bore mk2 amals on long inlet manifolds. The compression ratio is low. The motor was built in the 1980's and has been raced since with no problems and usual maintenance. It has 58 rear wheel horsepower and 58 ftlb torque.

Built in the 80s and raced ever since! Well you've certainly got something right !

SteveA · Oct 1, 2017

Thruxton said:
I run a 920 engine in my race bike. It has mk3 cases bored to take the sleeved 850 cylinder with a Mick Hemmings big valve head. Denco lightened mk3 crank, carrillo rods, 4S cam. Rita ignition. Running 36mm smooth bore mk2 amals on long inlet manifolds. The compression ratio is low. The motor was built in the 1980's and has been raced since with no problems and usual maintenance. It has 58 rear wheel horsepower and 58 ftlb torque.

Sounds good. What frame is it in and where are you racing it?

Interestingly my 750 short stroke can match or improve on your RWHP figure, but I would expect a very different torque curve and rpm limit! I don't think there is any shortage of torque from my motor, but they would not ride the same.

Fast Eddie · Oct 1, 2017

As Thruxton said Steve, the motor is low compression, so I'd say that's where he's losing power. And perhaps where he is gaining longevity !?

Brooking 850 · Oct 1, 2017

Hi Thruxton, even though the 920 sounds reliable after all these years, the rwhp seems quite low for a 920 with a big Vv head and all those other goodies to match.
I am using a RH10 head with standard vvs, standard manifolds, 32mm Premier carbs, 0.040" over in the bore and up until recently a standard crank.
JS2 rods and pistons and a JS2 cam, this is my race motor and makes well over 70 rwhp.
My compression is only 10.5 : 1 so im suprised your 920 puts out 58 rwhp
Regards Mike

acotrel · Oct 1, 2017

Wasn't 70 BHP claimed for the JPN - a 750cc engine ?

worntorn · Oct 1, 2017

Brooking 850 said:
Hi Thruxton, even though the 920 sounds reliable after all these years, the rwhp seems quite low for a 920 with a big Vv head and all those other goodies to match.
I am using a RH10 head with standard vvs, standard manifolds, 32mm Premier carbs, 0.040" over in the bore and up until recently a standard crank.
JS2 rods and pistons and a JS2 cam, this is my race motor and makes well over 70 rwhp.
My compression is only 10.5 : 1 so im suprised your 920 puts out 58 rwhp
Regards Mike

Different Dynos read a lot differently. Even when using the same dyno on the same bike on a different day some room for error is created.
Comparing two different bikes dynoed on different machines at a different location,time elevation etc gives really no meaningful info for comparison.
On a track, the bike dynoed at 58 rwhp might outdo the bike measured at 70 .
In fact this happened quite recently with a couple of race Nortons we are all quite familiar with. The one with the lower dyno number left the high number bike for dead on a long straight.
I can't say more, the Norton Police will get me.

Glen

SteveA · Oct 1, 2017

acotrel said:
Wasn't 70 BHP claimed for the JPN - a 750cc engine ?

Norman White told me the best they got in the '70s was 76, but at the crank, not RWHP. However, what is the relevance of the comment?

Brooking 850 · Oct 1, 2017

Hi Glen point taken. Will say no more
Regards Mike

Thruxton · Oct 1, 2017

Thanks for your questions. As I said in an earlier post my bike was built in the 1980’s with what was available at the time. The chassis is Norton Commando. It has 850 triple trees; the steering head is re-angled steeper. It has a Norvil style head steady. The rims are 18 inch with Norton hubs with Avon race tyres. The transmission is Quaife 5 speed, the primary drive is belt by Bob Newbury. It handles very well and has been electrically timed at 136 mph two way average with lower gearing than optimum for a flying mile. I aim for reliability rather than outright performance with my engine tune. At the last Mike Pero Classic meeting at Levels Raceway the bike completed over eighty laps throughout the weekend without a spanner on it. I have other race bikes but this is my favourite, fits like an old boot.
Below are links to the clubs I race with.
www.cams-racing.org.nz
http://bearsracing.co.nz/

Brooking 850 · Oct 2, 2017

Will you be racing at Levels this December?
If so I may well be there with mine.
Regards Mike

Thruxton · Oct 2, 2017

Yes Mike I hope to race at Levels this December. Did you race there last Classic festival? It is a great riders track my favorite. It would be great if you could make it. Look me up if you do number 52. regards Ren

Brooking 850 · Oct 2, 2017

If I go it will be the first time
Regards Mike #454

acotrel · Oct 3, 2017

worntorn said:
Brooking 850 said:

Hi Thruxton, even though the 920 sounds reliable after all these years, the rwhp seems quite low for a 920 with a big Vv head and all those other goodies to match.
I am using a RH10 head with standard vvs, standard manifolds, 32mm Premier carbs, 0.040" over in the bore and up until recently a standard crank.
JS2 rods and pistons and a JS2 cam, this is my race motor and makes well over 70 rwhp.
My compression is only 10.5 : 1 so im suprised your 920 puts out 58 rwhp
Regards Mike

Click to expand...

Different Dynos read a lot differently. Even when using the same dyno on the same bike on a different day some room for error is created.
Comparing two different bikes dynoed on different machines at a different location,time elevation etc gives really no meaningful info for comparison.
On a track, the bike dynoed at 58 rwhp might outdo the bike measured at 70 .
In fact this happened quite recently with a couple of race Nortons we are all quite familiar with. The one with the lower dyno number left the high number bike for dead on a long straight.
I can't say more, the Norton Police will get me.

Peter Williams with the JPN, giving away 25 BHP to the Japanese two-strokes was probably not all dyno error. What is 100 BHP if you cannot get on the road effectively and early coming out of corners ? There are two problems with gearing - Gear low and you can accelerate out of corners faster, but it doesn't help if you bike runs out of puff two thirds of the way down the straight. If you gear high, you often have not got the berries coming out of the corner, but you have the legs at the end of the straights. So in effect, you choose where you want to lose. If you gear high and turn and get on the gas earlier, you have the run on the other guy and still have the legs at the end of the straights. What amazes me about Peter Williams is that he beat the 750cc two-strokes in the dry. In the wet would be a lot easier.

Glen

Anyone as experience with 920 engine?

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