Atlas Engine Plates for Wideline?

marinatlas said:

Hi Nigel, good to know .......as I will purchase some to build up a Cdo engine into a slimline , I am looking after TGA (same as Molnar ?) any thoughts ......and no I will not build them myself !
and to hijack a bit what are your thoughts , vertical or tilted ..........as I have a spare old Maney 2/1 exhaust , a tilted seems the way to go but ??

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I have no experience with Andy’s engine plates, I can only say that what I have had from him has always been good. I did once plan to build a featherbed Commando and was actually planning to use his plates, and yes, I was gonna tilt the engine to allow use of a 2:1 pipe too!

Triton Thrasher said:

To say Converta plates are “shit” is too categorical. If you specifically mean Converta plates for an Atlas with an Atlas engine, I have no experience, but:

I can only estimate the road miles on my Converta Triton plates from Unity Equipe at something like 80,000 on a pretty vibratory Triton. The frame has cracked in two different places that time. Are Norton frames shit?

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Fair point, well put. Shit is a tad vague!

Actually I talking about Triton and Tribsa plates. But let’s not lose sight of my main point, which was simply to state that 1/4 plate is fine. I added the Converta comments as I believe that such failures can and have led people to conclude that 1/4 is too weak, and I wanted to emphasise that is not the case.

I have no grudge against Converta plates. And if yours a performing fine, thats great!

I’ve had 4 sets break in one place or another, one was an old set cracked before I got the bike. Two were new, and one of those sets also had misaligned holes.

The first set below are not the Converta style, you can see there is more material, in general, above and below the gearbox.

The Converta plates are ‘tapered‘ in shape and I’ve had them crack at the slot, at the shallow points near the upper rear mounting point and the lower rear. I also don’t like the fact the bottom crankcase mounting point is a slot rather than a hole as I’ve had one lose its shape here.

I have to confess though, I am mainly talking about race bike experience here. And one bike in particular vibrated horribly and probably unfairly stressed the plates.

It’s fair to say that Unity were suppliers to cafe racers, rather than to racers.

Triton Thrasher said:

It’s fair to say that Unity were suppliers to cafe racers, rather than to racers.

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Perhaps. But a lot of low budget racers (like me) shopped there quite a lot !

I bought or tried to buy Manx parts from Unity several years ago. They charged me for parts on 'backorder' and never delivered. Never. Did ship a few parts which in no way resembled actual Manx parts. Absolute shit. Can't believe they stayed in business.

Fast Eddie said:

Fair point, well put. Shit is a tad vague!

Actually I talking about Triton and Tribsa plates. But let’s not lose sight of my main point, which was simply to state that 1/4 plate is fine. I added the Converta comments as I believe that such failures can and have led people to conclude that 1/4 is too weak, and I wanted to emphasise that is not the case.

I have no grudge against Converta plates. And if yours a performing fine, thats great!

I’ve had 4 sets break in one place or another, one was an old set cracked before I got the bike. Two were new, and one of those sets also had misaligned holes.

The first set below are not the Converta style, you can see there is more material, in general, above and below the gearbox.

The Converta plates are ‘tapered‘ in shape and I’ve had them crack at the slot, at the shallow points near the upper rear mounting point and the lower rear. I also don’t like the fact the bottom crankcase mounting point is a slot rather than a hole as I’ve had one lose its shape here.

I have to confess though, I am mainly talking about race bike experience here. And one bike in particular vibrated horribly and probably unfairly stressed the plates.

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Re your QUOTE " one bike in particular vibrated horribly "
No tubular frame will withstand these stresses, I have to ask did you fit a suitable heavy gauge metal headsteady?

wot said:

I bought or tried to buy Manx parts from Unity several years ago. They charged me for parts on 'backorder' and never delivered. Never. Did ship a few parts which in no way resembled actual Manx parts. Absolute shit. Can't believe they stayed in business.

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I found them reliable and friendly, in the days before Bantam John bought the stock. But yes, they sold some shoddy stuff cheap.

Have you looked on e bay?
I like these. Stainless no less

Hi Chris, did you mean those plates ........?

Bernhard said:

Re your QUOTE " one bike in particular vibrated horribly "
No tubular frame will withstand these stresses, I have to ask did you fit a suitable heavy gauge metal headsteady?

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Yes it did.

The crank balance had been cocked up I believe. I had it balanced by Owen Greenwood, who was a good egg and clearly knew better, I reckon he just got it wrong. I eventually had the crank re balanced by Bassett Down and it was sweet.

But like I said, my reason for mentioning the excessive vibration was simply to state that it was probably not fair to blame the Unity plates for cracking that time.

I realise it was a long time ago, but what did Bassett Down say about your crank balance?
Owen Greenwood was that 3 Wheel Mini racing fame, and should have stayed out of Triumph engi engine tuning judging by your comment.

Bernhard said:

Except, Atlas engines are tilted backwards in the f/b frame.

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Thats an interesting comment. I certainly agree that it looks that way with some bikes. But how is it done? I had assumed it was the fitting of 18" rear wheels and lower profile rear tyres. Otherwise it would mean special engine plates , if so why??.

The road going featherbed frame was originally developed for the 500 Dominator, over boring and stretching the stroke almost made it impossible to fit without some major alterations.
Also there where no lower profile rear tyres available at the time, the 18 inch tyre had a near as damit rolling radius as a 19 in one. The Atlas, I assume came with an Avon GP rear tyre in the early 1960s. Not - strike that, never available in 19 in.

norton bob said:

Thats an interesting comment. I certainly agree that it looks that way with some bikes. But how is it done? I had assumed it was the fitting of 18" rear wheels and lower profile rear tyres. Otherwise it would mean special engine plates , if so why??.

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Bernhard said:

The road going featherbed frame was originally developed for the 500 Dominator, over boring and stretching the stroke almost made it impossible to fit without some major alterations.
Also there where no lower profile rear tyres available at the time, the 18 inch tyre had a near as damit rolling radius as a 19 in one. The Atlas, I assume came with an Avon GP rear tyre in the early 1960s. Not - strike that, never available in 19 in.

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I think we are talking at cross purposes. I was not saying that back then the tilted back look was caused by 18" wheels or low profile tires, but thats very likely what we are seeing now , as the range of tyres is better in 18" sizes and in fact UK atlases were often supplied with 19" as was ours. The current 19 tyre fitted is very much lower in profile than the SM often fitted , I measured a 2" overall diference in hight from a SM tyre to a modern Avon. (both 19") Probably why it now feels undergeared. I don't think there is any difference in the Engine plates . The 650 found the extra room in the cases by making a bulge in the back of the case and then offsetting the cylinder axis from the crank axis for the 750. There have been 750 motors in 500 cases built and raced. The Atlas does look tilted though !!. Did they raise the front frame mounts when the turned them round to stop the breakages??,could be.

Re: engine tilt

I addressed this in another thread. ...Reply #18. https://www.accessnorton.com/NortonCommando/carb-angle.24842/

According to my measurements, the barrel to head surface is parallel to the upper frame tubes, except for a slight rearward tilt of 0.35 degrees, which is so small it might be due to manufacturing tolerances, or my own measurement error.

It does not seem plausible that Norton would intentionally machine in a tilt of 0.35 degrees for no apparent reason.

Slick

Bernhard said:

I realise it was a long time ago, but what did Bassett Down say about your crank balance?
Owen Greenwood was that 3 Wheel Mini racing fame, and should have stayed out of Triumph engi engine tuning judging by your comment.

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I can’t recall what they said now. Greenwood was also a noted Triumph tuner, so he did know his stuff.

Personally, I have always kinda assumed he got two customers pistons mixed up. Mine were the big lumpy 11:1 Powermax things. If another crank was being balanced with lighter stock pistons, maybe that was the issue? If so, some other poor sod also probably had the same issue !