Author Topic: The problems of running 20,000 rpm  (Read 4880 times)

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Offline lordmoonpie

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The problems of running 20,000 rpm
« on: June 16, 2010, 11:34:20 PM »
Latest project is underway (Sam - don't move me to the project section just yet!! :D) and I'm building a 20,000 rpm 250-4 RC163 replica.
I've torn the engine down already, mainly becasue I love doing that and am impatient. The gear driven cams leave today for a bit of a tweak - the gears mean that no massive performance gains are possible without keying and indexing the gears, expense I don't want to go to. The crank goes off later to be lightened and balanced and polished and the head will go off for some porting, gas flowing and maybe some valve treatments if they can find lighter stainless valve train for these tiny tiny parts!

So the first question has hit - the bike will rev to 18,000 rpm in standard trim quite happily so the conrods must be pretty good, even though they are as thin as your average pencil. I can have the rods polished to reduce oil collection on them and just re-install them, or, I can go the expensive route and have a set of custom rods made for strength and reliability, using latest design technology. Given the engine is already capable of 18,000 rpm, do you engine gurus out here think I can get away with polising them or should I go for the custom rods for piece of mind? If it helps, I plan to get custom HC pistons done too which will be better design than standard and 20-30% lighter...

Thoughts?.....Anyone?! :D
1994 Ducati 888 SP5
1951 Ducati 50cc Cucciolo
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Offline scottly

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Re: The problems of running 20,000 rpm
« Reply #1 on: June 16, 2010, 11:41:39 PM »
Latest project is underway (Sam - don't move me to the project section just yet!! :D) and I'm building a 20,000 rpm 250-4 RC163 replica.

Thoughts?.....Anyone?! :D
Since you said anyone.. Jeez, pics please!!!! 
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Offline turboguzzi

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Re: The problems of running 20,000 rpm
« Reply #2 on: June 16, 2010, 11:49:40 PM »
Nice LMP, is it based on a CBR250 motor?

My thoughts are that you should do a quick calc of mean piston speed, that's the best indicator of how near you are to mechanical disaster. up to 22 m/sec is OK-ish

18-20k might sound crazy to some but considering the tiny stroke of that motor, might be just as safe as a 750 at 9K.

TG

Offline scottly

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Re: The problems of running 20,000 rpm
« Reply #3 on: June 16, 2010, 11:54:48 PM »
I remember reading about a Suzuki 3-cyl 50CC bike in the '60s that spun that fast; had a 500 RPM power-band, and something like a 14 speed gearbox...?
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Offline fastbroshi

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Re: The problems of running 20,000 rpm
« Reply #4 on: June 17, 2010, 01:59:58 AM »
Have you thought of cryogenically treating them?  I've heard good things about the process
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Offline Sam Green Racing

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Re: The problems of running 20,000 rpm
« Reply #5 on: June 17, 2010, 03:39:39 AM »
Simon, leave it all stock and be satisfied with 18,000rpm, they will rev higher but the rods stretch and the pistons clatter the valves, it's been done before.
If you don't want oil sticking to the rods, have them ceramic coated, it adds no weight as coating is only microns thin, it's proven technology.

Sam. ;)
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Offline Phil

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Re: The problems of running 20,000 rpm
« Reply #6 on: June 17, 2010, 03:51:36 AM »
Hi Lord Moonpie

I also have one of these mini-beasts waiting in the wings (must finish the CR750 & Dresda GL1000 first!) and am mesmerised by the engine. I went to Spa Francorchamps last weekend and there were several superb RC163 replicas there and I took great interest in them. Some, not all, literally screamed and must have attained 20,000+ rpm cleanly whilst others misfired at high revs. Some have the Keihin FCR carbs and others did not but some were running well on standard carbs without the airbox (incidentally, I already have a jet-kit to permit standard carbs and no airbox). I am no expert on the engine but have done some research in Japan via my contacts at Honda who have reported that the engine is pretty well unbreakable, even at very high (20,000) revs. It is common in Japan, apparently, to fit FCRs and a new ignition module to everyday roadbikes make these incredible engines rev to 20,000 rpm and 22,000 has been reported! I am told that 'the engine was an exercise in attaining high rpm by using 'very low mass and perfect balance'. I was told this personally by an HRC technician I first met when I worked for Bel Ray in the 1970s and we were involved on the lubrication of the NR500. I asked if tuning equipment was available and he said it was not possible to tune it more - so there is a challenge!! I intend to fit FCRs, the modified ignition module, "blueprint" and remove the alternator. There is a "story" at Honda that Irimajiri, the lead designer of the Honda RC174 (250-6) was given a "clean sheet" to design a road bike engine as his legacy before he retired. Apparently, the result was the CBR250RR. These engines running open exhausts do sound like nothing else!

Offline turboguzzi

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Re: The problems of running 20,000 rpm
« Reply #7 on: June 17, 2010, 04:30:45 AM »
lmp, just checked, stroke is 33.8mm (take a ruler in your hand guys :) ), indeed half of a 750's..... @ 20K you get exactly 22 m/s, high but nothing special these days, you are good to go...


Offline kos

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Re: The problems of running 20,000 rpm
« Reply #8 on: June 17, 2010, 05:40:28 AM »
Just get a hold of the re-maped ignition box from Japanese domestic models and 21K is yours. OEM rods are fine on these. I built and sold two of them and my customers never had problems once they sorted out the carburation problems.

KOS
220...221, whatever it takes.

Offline Sam Green Racing

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Re: The problems of running 20,000 rpm
« Reply #9 on: June 17, 2010, 06:06:18 AM »
At 7 seconds, my mates rep.


Sam. :)
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Offline lordmoonpie

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Re: The problems of running 20,000 rpm
« Reply #10 on: June 18, 2010, 05:18:17 AM »
Brilliant stuff - thanks guys! Phil, it's a shame you don't live nearer, it looks like we have a lot of stuff developing in common. Good to hear from you too Mark with proof of the capability of the engine.

So, cams are off for a minor update - nothing radical becasue of he gears, crank will be lightened and balanced, again just 5% or so and the pistons reworked to produce 25% lighter items. The head will be ported, flowed and fitted with new valve guides and *hopefully* custom made lighter valaves. Springs will be kept standard and I think rods too. I will look into DLS coating the piston pins too.

I plan on getting FCRs but becasue they are a nightmare fit in the replica RC frame I have, I'm going to get the intake stubs on the head dropped by 5 degrees to clear the frame raisl with the carbs.

Pictures! Ah yes, I'll get some of the bits as they go out for work as "Before" pics. I have to agree with you Phil, the engines are amazingly small and the parts just beautiful. I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.

I'm also having discussions about whether the clutch is too deep to engineer a dry clutch onto it - now that would make them a super replica.

Phil - one of the RC replicas at Spa is an email pal of mine who just completed his excellent bike - chap called Stuart. His is the pinup bike I aspire to for the time being :-)
1994 Ducati 888 SP5
1951 Ducati 50cc Cucciolo
1981 Yamaha XV750 SE

Offline turboguzzi

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Re: The problems of running 20,000 rpm
« Reply #11 on: June 18, 2010, 05:30:36 AM »
I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.


valve spring compressor to disassemble the valves? We are in the 21st century mind you :)

put a suitable sized socket on an socket extension, hit with a hammer. Done. 5 seconds per valve.

TG

Offline livefast_dieold

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Re: The problems of running 20,000 rpm
« Reply #12 on: June 18, 2010, 12:02:23 PM »
I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.


valve spring compressor to disassemble the valves? We are in the 21st century mind you :)

put a suitable sized socket on an socket extension, hit with a hammer. Done. 5 seconds per valve.

TG


I use the same method too :-)
And for reassemble them I use my grandfather's bottling machine  ::)

Offline lordmoonpie

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Re: The problems of running 20,000 rpm
« Reply #13 on: June 18, 2010, 12:07:18 PM »
Nice trick TG - I'll try that. I think knowing my luck it'll end up being subject to the first law of the garage - if a small part (like a valve collett) can fly off and end up in a dark corner of the garage where it won't be found for years, it probably will!

I'll give it a go tomorrow - re-assembly is a "tomorrow" job  ;D
1994 Ducati 888 SP5
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Offline turboguzzi

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Re: The problems of running 20,000 rpm
« Reply #14 on: June 18, 2010, 12:52:38 PM »
Nice trick TG - I'll try that. I think knowing my luck it'll end up being subject to the first law of the garage - if a small part (like a valve collett) can fly off and end up in a dark corner of the garage where it won't be found for years, it probably will!

I'll give it a go tomorrow - re-assembly is a "tomorrow" job  ;D

OK, just dont bang your thumb with the hammer, you need to hit the extension, OK?

There's a tip to mount the colletts back in 5 seconds too, trickier though :)

get back to me on the subject when you are buttoning up the motor ;)

+ where's my prize for the monoshock trivia question?

TG

What's up Ricc? got the thing running without bending valves at last?




Offline livefast_dieold

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Re: The problems of running 20,000 rpm
« Reply #15 on: June 18, 2010, 05:51:08 PM »

What's up Ricc? got the thing running without bending valves at last?



Working hard, but not on bikes! I gave the motor to a friend of mine to make some space for the valves, probably next week it would be back in the frame ready for next race (last new: 17 july in Adria for vintage endurance). How you doing?

Offline lordmoonpie

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Re: The problems of running 20,000 rpm
« Reply #16 on: June 22, 2010, 05:11:42 AM »
I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.


valve spring compressor to disassemble the valves? We are in the 21st century mind you :)

put a suitable sized socket on an socket extension, hit with a hammer. Done. 5 seconds per valve.

TG

Worked like a dream TG and only needed a gentle tap. Took more than 5 seconds per valave though just because the collets are so tiny I could barely pick them up to put them away safely! The valve stems look like they're about 2mm thick - amazing engine....
1994 Ducati 888 SP5
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1981 Yamaha XV750 SE

Offline Sam Green Racing

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Re: The problems of running 20,000 rpm
« Reply #17 on: June 22, 2010, 06:58:03 AM »
Think what they must have been like in the 250/6 the 5 cylinder 125 and 50cc twin :o :o :o

Sam. ;)
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Offline turboguzzi

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Re: The problems of running 20,000 rpm
« Reply #18 on: June 22, 2010, 09:26:33 AM »
I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.


valve spring compressor to disassemble the valves? We are in the 21st century mind you :)

put a suitable sized socket on an socket extension, hit with a hammer. Done. 5 seconds per valve.

TG

Worked like a dream TG and only needed a gentle tap. Took more than 5 seconds per valave though just because the collets are so tiny I could barely pick them up to put them away safely! The valve stems look like they're about 2mm thick - amazing engine....

Happy to hear LMP, but for those tiny parts there's another 21st century invention.... a small magnet on an antenna stick :)

one of my more used tools, lets you pull out nuts and washers from crazy places too, I even use it to get nuts  started on studs in recessed areas.

get one!

TG

Offline lordmoonpie

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Re: The problems of running 20,000 rpm
« Reply #19 on: June 22, 2010, 12:25:43 PM »
I can't take the valaves out currently until I've made an adaptor for my valve spring compressor - these things are tiny.


valve spring compressor to disassemble the valves? We are in the 21st century mind you :)

put a suitable sized socket on an socket extension, hit with a hammer. Done. 5 seconds per valve.

TG

Worked like a dream TG and only needed a gentle tap. Took more than 5 seconds per valve though just because the collets are so tiny I could barely pick them up to put them away safely! The valve stems look like they're about 2mm thick - amazing engine....

Happy to hear LMP, but for those tiny parts there's another 21st century invention.... a small magnet on an antenna stick :)

one of my more used tools, lets you pull out nuts and washers from crazy places too, I even use it to get nuts  started on studs in recessed areas.

get one!

TG
Yeah I did use one of those TG - I'm not living entirely in the dark ages. Problem is you still have to pick the little suckers off the end of the magnet LOL!
Sam- you're right there, the tiny multis must have been more akin to working on a watch than an engine!!
1994 Ducati 888 SP5
1951 Ducati 50cc Cucciolo
1981 Yamaha XV750 SE