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 Starter clutch

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bobdixon




PostSubject: Starter clutch   Mon Dec 06, 2010 2:07 pm


I thought I'd drop the forum a quick line about my experience with the starter clutch. If you detect any slippage from the starter clutch you should take it very seriously because if the clutch is fretting it can deposit very harmful debris into your oil. I tried fitting new rollers and springs but the problem persisted. My Atlas motor runs at 11.8 to 1 compression and 40 weight Castrol R and these combined forces means that the starter clutch has a hard time.
I contacted Leo who advertises on this list and he recommended fitting an oversize roller starter clutch. When the unit arrived I was extremely impressed with the engineering quality, it's a far superior unit to the standard item. I'm absolutely delighted with the new unit [thank you Leo] . I've been working on the bike this morning and it started instantly in temperatures of minus 5. Leo's units are quite expensive [and justifiably so] but they are worth every penny. As Sir Henry Royce once said; the quality is remembered long after the price is forgotten...
Bob
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kiwi

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PostSubject: Re: Starter clutch   Mon Dec 06, 2010 9:35 pm

Hallo Bob,

Leo will be happy about your judgment, I have seen his starter clutch he made a real good job.
Your Atlas Motor runs at 11.8 to 1 compression, what did you to get it so high?

How runs the Bike with this high compression?

Greetings from Switzerland
Bruno
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bobdixon




PostSubject: Re: Starter clutch   Tue Dec 07, 2010 2:17 am

Hi Bruno,
My Atlas engine is fitted in an endurance racer and has been equipped with high comp 78mm pistons . This are F2 pistons and would normally give a compression of 10.5 to 1. With the Atlas stroked crank the compression is higher and the total capacity is 603cc. The engine is also fitted with S1 Montjuic cams and an F500 close ratio gearbox . I have also altered the valve timing and reduced the overlap which has improved the midrange torque.
The Atlas engine is a superb engine to tune and can be modified far more successfully than a standard 500. I have stripped both a 500 and an Atlas on the bench and the Atlas has an impressive amount of detail improvements.
I should re-assure Atlas enthusiasts by stating that I didn't break a healthy Atlas to obtain the motor. It came from a friend who had purchased the engine from a write -off!
Bob
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kiwi

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PostSubject: Re: Starter clutch   Tue Dec 07, 2010 10:02 am

Hi Bob,

wow, it sounds great what you did with the Atlas engine, it looks like it is a real racer. So your engine must have between 60 and 70 hp or even more?
You altered the valve timing and reduced the overlap to get more midrange torque, how did you do this?
Do you build a new camshaft for this?
Midrange torque is the thing I really miss on the Atlas and probably the most other Atlasrider too. Have you got an idea how to change this without to build
a new engine? Which Carburetor du you use on your bike?

It would be very interesting for all of us in the registry to see pictures of your bike and the Atlas engine. (Please send it do the Admin)
Of course we would like to hear the results you did on the racetrack.

Bruno
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bobdixon




PostSubject: Re: Starter clutch   Tue Dec 07, 2010 11:25 am

Hello Bruno,
The cams are S1 [Formula500] specification and we carefully elongated the sprocket mounting holes so that the timing can be altered. I haven't got the Atlas timing figures so I can't comment on the standard settings. The factory recommended setting for the S1 is quite 'peaky' and this is what we were trying to eliminate. I haven't got my notes to hand but I think we used 106 degree lobe centre timing.
The cylinder head has been very carefully ported and has 3 angle valve seats, re- profiled valves etc etc and runs on 36mm Dellorto pumper carbs.
I'm not sure what the horsepower is but I would estimate above 70bhp.
Even though the bike is very powerful it starts very easily and ticks over very nicely. I have set the rev limiter at 8600rpm. I think the biggest improvement probably came from the porting modifications.
Regarding other modifcations I have removed the balancer shaft and the heavy helical primary gears, which have been replaced with 500 straight cut gears.
It runs on Sachse ignition and Dyna mini coils.
The bike weighs 149kg dry and so it has a good power to weight ratio.
I'm happy to share pictures so I'll try and send some to admin.
This season has been mainly development and threfore I can't claim any race success with the bike, although the team I ride for [www.laverdacorse.it ] has had a good season in EUM Vintage Endurance cup. We've been ridingF500 specification 500s although we used my bike for a meeting at Rijeka but sadly there was a small fault with Sachse ignition rotor and we retired early. Next season my bike will entered in 4 endurance races .
Regards, bob
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bobdixon




PostSubject: Re: Starter clutch   Tue Dec 07, 2010 1:30 pm

Hi Bruno, I've posted a small gallery of images for you.
Bob
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kiwi

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PostSubject: Re: Starter clutch   Tue Dec 07, 2010 8:01 pm

Hy Bob,

thank you, the pictures are brilliant,
I couldn't imagine that the Atlas is such a beautiful bike, the only ones I know are the dirtbikes:-)))

The Sound of this exhaust must be incredibly like Bach or Chopin!
I have to hear and see the new Atlas, where are the 4 endurance races next year? I hope not too far away from central europe.

Bruno

P.S. more pictures please
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bobdixon




PostSubject: Re: Starter clutch   Tue Dec 07, 2010 9:06 pm

Hi Bruno,
The bike has a very unusual sound, very deep and mellow but at high revs it howls like a 2 cylinder GSXR! It's very different from a standard 500.
Having got rid of the heavy balance shaft and the helical primary drive the throttle response is very fast indeed, very different to a standard Atlas.
The bike is road registered in the UK so occasionally I take it out for some fun and it's surprisingly fast, easily as quick as a Jota.[it has a similar power to weight ratio]

The team will be mainly racing in Italy next year, the series has rounds at Adria [near Venice], Francaciorta[Milan], Magione [Umbria] and Rijeka in Croatia.
Last year we came 1st ,2nd and 3rd in the 500 class championship. This year we will be entering two 500s in the 500 class and I will using my Atlas engine machine in the 750cc class.
I've posted a few more pics. In the next few weeks I will posting a complete write up on how we built the engine on my website www.laverda500.cc
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kiwi

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PostSubject: Re: Starter clutch   Fri Dec 10, 2010 10:39 am

Hi Bob,

to listen to the great Atlas sound would be Francaciorta (Milan) possible for me, this is just about 250 km away. Do you know the date of this race?

I'm waiting for your compete story how you built the engine. If you have forgotten the most thing to writing your story, I'll bring you one of my Atlas engines, so you can start again:-)

Greetings from Lucerne
Bruno
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Nick

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PostSubject: Re: Starter clutch   Sun Jan 02, 2011 8:08 pm

Bob,

I'd be interested to see some pictures of Leo's unit next to a standard one. Also does Leo's unit require alternative springs, plungers and rollers to the original - I ask as sourcing RGS parts is easy in the UK and wonder if this unit does require an overhaul if parts have to come from Leo.

The whole breaking starter sprag, poor starting has blighted my enjoyment of the Atlas. I don't really know if it is the sprag or whether the breaking sprag is a result of the slow cranking speed.

Thanks

Nick
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bobdixon




PostSubject: Re: Starter clutch   Mon Jan 03, 2011 8:27 pm

Hi Nick, I haven't got a back to back photographic comparison but I'm sure Leo could help with that. The units are identical in size although on Leo's advice I ordered mine with oversized rollers [10.2mm? instead of 10mm] because the boss on my starter gear had worn so it was undersize.
A worn starter clutch will cause the cranking speed to slow because the clutch will slip every time it tries to throw the motor over its compression stroke.
My worn starter clutch actually created the symptoms of a flat battery.
The standard 10mm rollers as used in Leo's clutch are easy to find should you ever need spares, oversize rollers are listed in most engineering catalogues but there is usually a minimum quantity that need to be purchased. I don't know the spec on Leo's springs, but I'll worry about that when the time comes!
Bob
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Nick

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PostSubject: Re: Starter clutch   Mon Feb 07, 2011 10:37 pm

Well I think I have fixed the starter sprag. I ordered a replacement sprag from Leo and that is sitting on the bench - very nice too. In the process of getting the replacement sprag I wondered if the original sprag could be used simply by installing oversize rollers - and it can at least on my machine. My starter gear measured 49.6mm so I had a set of 10.3 rollers made up and it has now worked for the past two weeks (1700 kms). Leo's sprag is a quality item and there as insurance but I may have found a short-term alternative.

The other thing I have learned is how to start my Atlas. I had been experimenting with the choke position but the big mistake I made was to slightly open the throttle on start up - as you would on most bikes. With MY Atlas the procedure seems to be to put the choke on full and then just hit the starter button without a hand on the throttle. The engine catches and once running the speed is then controlled by backing off the choke and holding it on the throttle.

Seemingly sorting both the sprag and the starting has made a big difference to Atlas ownership - revving it out of bends to 7,000 rpm is quite infectious...

Nick :-)
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kiwi

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PostSubject: Re: Starter clutch   Sat Feb 12, 2011 7:20 pm

Hi Nick,

"With MY Atlas the procedure seems to be to put the choke on full and then just hit the starter button without a hand on the throttle. The engine catches and once running the speed is then controlled by backing off the choke and holding it on the throttle."

This procedure of course I have to try.
Does Start your Atlas easier with the new oversize rollers?
Still the feeling of flat Battery?

Bruno
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Nick

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PostSubject: Re: Starter clutch   Sun Feb 13, 2011 12:29 pm

Hi Bruno,

Yes the starting has improved a lot since I put in the larger rollers. There is now no slip on the starter gear so it turns over quickly and consistently. The oversized rollers have now covered a further 1,000 kms without trouble, so the 'fix' seems good. I have also put in an better battery an SVR 15L http://www.tayna.co.uk/SVR-15L-Sealed-AGM-Motorcycle-Battery-YB14L-A2-SVR15L-P7731.html - this has better cold cranking than the previous battery and is the best I could find to fit in the limited space. I think however the main problem was the starter sprag and will probably use the old 'lower spec' battery in the summer when you don't need the same cold cranking.

The poor starting has cost a lot of wasted money and time but hopefully what I've learnt may save other owners from all the hassle!

Nick :-)
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FRRRanky

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PostSubject: Re: Starter clutch   Mon Feb 14, 2011 11:09 pm

Nick wrote:
Hi Bruno,
I have also put in an better battery an SVR 15L http://www.tayna.co.uk/SVR-15L-Sealed-AGM-Motorcycle-Battery-YB14L-A2-SVR15L-P7731.html -

Hi

I can confirm the positive effect of a new, powerfull battery of AGM- or gel-type on the starting behaviour. I put a gel-battery and you have the impression the Atlas starts with only looking at the starter button
I'll add the make SVR to the "tips & tricks / electrics" section of the website. Keep in mind, nearly all makes finally sell the same products, as there's only 2 or 3 battery producers in the world (that means: China), so go for the best offer.

Frank


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Nick

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PostSubject: Re: Starter clutch   Sun Aug 19, 2012 4:25 pm

Well I followed the lead of Bob Dixon and fitted a sprag out of a Zane bike after the Swiss clutch started to cause the same problems as the original. Some tips:

You will need to shim out the Zane sprag to line up with the idler gear.
You have to use the Zane idler gear also - this must be modified to fit the Atlas case which means the outer step has to have its diameter increased to 21 mm up from 19mm and the depth increased from 8mm to 14mm.

The Zane sprag uses sprag bearings not roller, plungers and springs which gives more grip. In addition the Zane sprag has lower gearing so spins the engine quicker.

Nick
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