Parts info required from the brains trust

seven4nineR

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Mr.R

Here's the part number for the "Red" bolt :-
77910292A
Drilled Screw M8X75 MR/04
I just happened to have my one sitting behind me as I read your post. 😏

I'm using NOS late ST4 cases for my 955 motor, these have all the strengthening and oiling mods incorporated from the 851/888/926 racing program as standard.
I've still to get them machined to take the 96mm id 102mm od barrels...
Although I've been told that it's better to turn down the od of the barrels to 101mm and machine the crankcases to suit for extra strength..

Steve R

stafford

I spoke recently to a race team manager from the early 90's and was surprised to hear that cranks were not balanced and cases had an expected life of 500 miles. So having balanced your set you may have already cured the issue, except for the upgrade on oil feeds that Mr R mentioned.

Mr.R

As cranks are originally ballanced at the factory even on road bikes, I very much doubt that the race bikes weren't??
All of the top engine builders/blue printers, race bike tuners etc will always ballance the cranks in their race motors.
If you look at almost any pic' of a race 888 motor stripped down, you can see the ballance factor's adjustment figure needed/carried out marked on the cranks and the primary gears.
They've all also got either or both holes drilled to lighten or heavy metal (Mallory metal) plugs added to ballance them.
Over the years I've stipped quite a few Ducati motors (or any others come to that) and this has always been the case.

The reason that the cases broke/cracked on the 851/888 race motors was because they were weak in their design/not upto the high revs that the race motors went to.
Hence the upgrades/modifications/redesigns in the later cases.

Steve R

stafford

Just passing on information from the horses mouth.

Mr.R

Fair enough Stafford.
But I think that on this occassion it wasn't so much the horses mouth, but more his arse!
I personally ballance anything that's over 2" in diameter like the timing gears etc and make sure that all other like parts weigh the same, or as near as possible.

Steve R

griff851

My 2cents. All cranks are balanced. All engines have an inherant vibration from the crank. By initiating the black art of crank balancing all your tring to do is push the vibration to a rev range where its not a pain in the arse (or hand ). Preferably somewhere you generally go through. So a good balancer will ask you what revs you generally ride at. On the single I'm playing with, it was initially 58%, vib started at 6k, took it up to 65%, and it started at 7500ish. This means that at 10-11k some of my teeth filling stayed in place. The factory used 70% (learned after doing the job). That would probably equate to hands still going numb, but my dental bill will be less. :-)

seven4nineR

Thanks!

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MonsterMadMarty

seven4nineR wroteanyone know where I can source new circlips for the pistons?

Not sure about compatibility but I have a heap of circlips part number: 88440111A they appear to be 1.5 wire & 22mm. I'm in Perth, WA & can post you a set if you think they are any good!

Cheers, Marty

seven4nineR

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marvin

Way back when my Brother and I used to build up stroker Harley engines we would balance at 56% The Harley is a 45 degree engine so they vibrate a lot. Aprillia's are 60 degrees so they vibrate also. Ducati twins are a 90 degree engine so a lot of the inherent vibrations cancel each other out. Probably the reason that Ducatis don't vibrate as much as an Aprillia.

Mr.R

Years ago when I was building race motors for Bevel twin Ducati's, I always had the cranks inc' rods, bearings, pistons complete with rings, pins and circlips to 50%.
This resulted in very smooth motors even with very lightweight highly modified cranks.
However a balance factor of 50% on my 851/916 motor, finds a rough patch at between 5,500-6,000rpm, not a problem on the track as you're through these revs in the blink of an eye.
But on the road this vibration patch sits around 100mph.
I'll have a chat with the balancing people to see if they can suggest a change in the factor? To move the patch somewhere less intrusive for my 955 motor.

Steve R