What do you think: balancing crank needed or not?

Mr.R

dudlington wroteMr R that is of course an interesting point keeping the revs below 10 grand for reliability. Maybe there could be a different thread concerning the benefits of a chassis mod connecting the swinging arm pivot point to the lower rear engine fixing point and moving the bearings from engine to swinging arm (As demonstrated by Spondon and copied on every Ducati model from the 916). Both my 1036 Testerstretta engined 888 and 1198 cc engine 851 have these modifications. Once that rev limit is lifted then there are any number of other tuning mods on the engine that could be performed in the quest for more speed and reliabilty. The crank lightening and balancing is a must because of this design flaw especially during racing to reduce stresses into the crankcases. Polishing of course brings performance gains but are very small in the big grand flawed scheme of things.

You do have a point there dudlington but...

The 851/888 cases breaking aren't due to the forces applied by the swinging arm, rather they're about the crank trying to escape between the V of the cylinders.
The crank hammering up and down at over 10K causes the cases to crack out from the main bearing housings, the 1st sign being a miss fire at higher revs.
This is why the 888 Corse cases were changed every 500 (or so?) racing miles.
It was for this reason that the cases were made stronger as the years of racing went by.
The later/last ST4 cases incorporated all of the lessons learnt from the 851/888/926 racing programme, so they're the strongest cases available to build a 851/888/926/955.
This is why I'm using a pair of NOS late ST4 cases for my 955 motor.

...and the OP did state that he was using 851/888 cases.

Steve R

dudlington

Mr R

I realise I,m getting into dangerous territory here (Hence the idea for a seperate thread) but here is what I read and seems to make sense. Once the extra forces from the swinging arm were neutralised by transferring them to the chassis it meant less opposing forces going through the crankcases. I read these machines could safely rev to a higher limit so producing more power and beating the competition. The design was copied by Ducati and used from then on................Interesting reading.

http://www.speed-trap.co.uk/spondon.htm

Sports Motor Cycles Spondon 888 Race Bike

Steve Wynne and Sports Motor Cycles had a long and glorious history of making race and championship winning bikes. Apart from the fairytale win for Hailwood in 1978, there were numnerous other championship wins including 4 TT F2 championships in the early 80's.

Steve worked with Spondon Engineering to create an alloy frame for the air cooled Ducati's (bevel and belt) and ultimately progressed to creating this. Work seemed to have started in 1987 and it obviously went well as they won the BoTT series in 1988 and the European BoTT in 1993. The bikes started off with a twin spar design, but by mid 1992 they had progressed to a single larger main spar.

Racing 8 valve Ducatis were (and still are) breaking crankcases and Steve W thought it might be down to the engine being used as a stressed member and having the stresses of the rear fork pivoting in the engine case. In this design the swinging arm does not pivot in the cases and stress the crankcases. With this design there were no more case failures.

crowster69

yeh sports still race one down in kiwiland.this one is now a 1026

dudlington

Yes please. I had a chance to buy a Spondon 851 a few years ago but it needed too much work and was not cheap. It was the orange bike right at the bottom of the link I sent , not the nicest looking 851 .................Would be nice to have one though.

So I think we all agree , balancing and lightening the crank is a must especially the higher spec/power/rev limit. The trick as someone pointed out on this thread is to balance the whole engine package with the chassis and not go toooooo far.

stiglarsenDK

Frame for around £3k ?

Interestig reading Paul

Story says : Steve W spends his time now restoring ultimate exotica) Spondon will still make you a frame for around £3k.

Is this still valid ?

Did they come in both mono and dual sided swinger ?

Ciao

dudlington

Stig

Yes Spondon chassis came with mono and dual sided swinging arms. Personally I do not think the Alluminium frame makes the bike look nicer............call me old fashioned but that trellis frame in white works everytime for me.

Interesting question would be : Could you still race in various events if you modded the trellis frame to pick up on the swinging arm pivot (incl. bearings). Effectively you could then have (in theory ?) more scope to explore the upper reaches of the rev range in the quest for more speed (But maintaining reliability).

Another question is : Has anybody done this to good effect (racing) ?????

Considering the work/cost you need to put into engine tuning at competitive levels to get power/reliability , it would seem this chassis mod/swinging arm mod is relatively easy and cheap (Get a scrap 748/916 type chassis and cut off what you need and weld on)...............or ?????

Foggy 888

While I do agree that having the frame support the swing arm pivot does reduce the load on the engine cases a little bit. But the main culprit in engine case longevity is how high you rev the engine. The loads on the engine cases increase with the square of the engine speed.
Going to the strongest engine cases possible and keeping the revs to a reasonable redline and you will have an engine that last forever. Start revving the engine to Chili specs 13k+ RPM and you will have an engine that lasts one qualifying session. I can remember when Ducati was replacing motors at WSB races like they were disposable. One engine for practice and qualifying, then replace it for the races.
I talked to Anthony "Slick" Bass about Fogarty's bike, and even in 1993 they would use an engine for the two races and the next races practice and qualifying, and then put a new one in for the next races.

A good motor built with ST4 cases and quality RS parts should last a few seasons of amateur racing if you keep the redline to reasonable limits. While knife edging doesn't do much, the polishing aspect removes flaws where a stress raiser could start to cause a crack. If you look at really good racing crankshafts (machined from billet), they are ungodly expensive. The crank for a Desmosedici is over $10k USD. But the part that takes the beating from over-revs is the crankcase. Keep the revs down and they will not crack.

seven4nineR

dudlington wroteStig Yes Spondon chassis came with mono and dual sided swinging arms. Personally I do not think the Alluminium frame makes the bike look nicer............call me old fashioned but that trellis frame in white works everytime for me. Interesting question would be : Could you still race in various events if you modded the trellis frame to pick up on the swinging arm pivot (incl. bearings). Effectively you could then have (in theory ?) more scope to explore the upper reaches of the rev range in the quest for more speed (But maintaining reliability). Another question is : Has anybody done this to good effect (racing) ????? Considering the work/cost you need to put into engine tuning at competitive levels to get power/reliability , it would seem this chassis mod/swinging arm mod is relatively easy and cheap (Get a scrap 748/916 type chassis and cut off what you need and weld on)...............or ?????

Interesting tangent this thread has taken, great reading.

It must help, but I'm not sure supporting the swingarm is the magic bullet we seek. From what I remember, and have read, the early 916 series bikes were still renowned for cracking crank cases, even when the swingarm was supported.

From an article in 2001, talking about early 916's:
"Crankcase failures continued to be a problem, to the point where five years ago a set of cases would last only one race meeting, but this improved when a bearing at the bottom pulley from the timing belt was altered, reducing a major stress centre."

But see below for what may be the best of both world's for supporting the swingarm, no frame mods required, just a simple bolt on mod. The pic is from an Aussie bike at Eastern Creek, but I wish I knew where the brace was from.......

Or you could follow the very successful Bob Brown/Kevin Magee approach back in the day and add some extra triangulation at what looks to be the obvious frame "hinge" point. Brown mentioned that this markedly improved crank case longevity, and you'd have to think it a stronger (if not prettier) solution than the gusset bracing the same point.

Speedmade

dudlington wroteStig Yes Spondon chassis came with mono and dual sided swinging arms. Personally I do not think the Alluminium frame makes the bike look nicer............call me old fashioned but that trellis frame in white works everytime for me.

How about this Spondon Ducati frame? It's the only one like it that they ever made

Foggy 888

It looks almost identical to the Spondon-Yamaha Formula Single race-bike that I used to race.
The asymmetrical "Banana" swing-arm was terrible on that bike. It would compress like a spring when loading the bike up in a corner, and then when the rear tire reached its traction limit, instead of sliding predictably it would just let go and high-side you to the moon. It put three different riders in the hospital.
It was worse with Michelin tires as they would grip and then let go instead of sliding as the Dunlops would. Didn't stop me from winning three championships on it. But in hindsight I would have ordered the bike with a conventional swing-arm.

brad black

i replaced the std pistons in my 750 engine with some ferracci ones (i think) that were 50 grams lighter and it made no difference at all to vibration. it still had a very narrow band vibration at 5,000 rpm too.

i've had a few engines balanced over the years and most (even some that the owners said were very nice) still felt much the same to me.

but if it is a customer engine and especially if it was going to see some rpm or track usage i'd recommend it. probably mostly as an arse protecting exercise (as in mine).

taking the ears off the crank takes about 400grams off.

jakepeewee

I am tempted going the carrillo's route for the SP3, but the project is getting bigger and bigger.
Was just gonna install 748R heads...

Don't know yet how much the steel H pankls weigh that are supposed to be in my bike (approx 500 gr?). I read that the carrillo's are supposed to weigh 402 gram, but found on ebay steel carrillo´s which weigh 451 grams.

It seems there are different conrods (see part numbers carrillo below):

DU-851<-8M4882S (402 gram)
DU851Z 54882 (451 gram, listed on ebay)

Did anybody know about these different types? Are the heavier ones older types or?

BTD

[QUOTE=jakepeewee;67468]I am tempted going the carrillo's route for the SP3, but the project is getting bigger and bigger.
Was just gonna install 748R heads...

Doing bike modifications is such a slippery slope!........Wanna buy I turbo I have for sale? Lol.

jakepeewee

[QUOTE=BTD;67510]

jakepeewee wroteI am tempted going the carrillo's route for the SP3, but the project is getting bigger and bigger. Was just gonna install 748R heads... Doing bike modifications is such a slippery slope!........Wanna buy I turbo I have for sale? Lol.

No, not yet that is

Besides the carrillo rods I am also tempted to go for ST4S cases

nine16

[QUOTE=jakepeewee;67515]

BTD wroteBesides the carrillo rods I am also tempted to go for ST4S cases

Do it right the first time and just do it once. Once its all done, you're much more likely to regret going half way than spending more to do it well.

That's what I told myself in my rebuild, anyway.

...and I was right. The motor is a beast. The bike is light. And it's scary-fun.

Mr.R

jakepeewee wroteI am tempted going the carrillo's route for the SP3, but the project is getting bigger and bigger. Was just gonna install 748R heads... Don't know yet how much the steel H pankls weigh that are supposed to be in my bike (approx 500 gr?). I read that the carrillo's are supposed to weigh 402 gram, but found on ebay steel carrillo´s which weigh 451 grams. It seems there are different conrods (see part numbers carrillo below): DU-851<-8M4882S (402 gram) DU851Z 54882 (451 gram, listed on ebay) Did anybody know about these different types? Are the heavier ones older types or?

There's several different Carrilo rods for these motors...
They have different size bolts for a start and some have a hole drilled up from the big end through to the small end for positive/pressure feed to the small ends.
Later rods have bigger/thicker bolts for extra strength and some of the earlier rods (like those fitted to the works/factory engines) have the positive feed to the small ends/piston pins.
If you use later ST4/ST4S cases there's no need for the pressure feed to the small ends as these later cases have oil sprayed up under the piston crowns from both sides of the cases.

Steve R

jakepeewee

So I am on the look out for a set of ST4s cases for not too much, but was wundering if there's a difference between ST4 and ST4s cases. Does anybody know?

And what about S4 cases? Are they the same?

Jacco

stiglarsenDK

jakepeewee wroteSo I am on the look out for a set of ST4s cases for not too much, but was wundering if there's a difference between ST4 and ST4s cases. Does anybody know? And what about S4 cases? Are they the same? Jacco

S4 and ST4 are to be used if your doner engine is 851,888 or 916 (case bore is 100mm, studs are same layout, etc)
If your doner is 996 based ... you are after S4r or ST4S....

jakepeewee

stiglarsenDK wroteS4 and ST4 are to be used if your doner engine is 851,888 or 916 (case bore is 100mm, studs are same layout, etc) If your doner is 996 based ... you are after S4r or ST4S....

Thanks!
And the cases are just as strong as the S4r and ST4S?

brad black

the cases are the same casting. the difference is the machining for the cylinder stud spacing/cylinder spigot.

2001 onward cases are better, you'll need matching oil pump and primary drive gears.

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