Motoscrubs.com

Hello Dave,
The original Ducati bearing is 32/39/18 which uses 3.5mm rollers, pin size 27/32/27. Big end cages should ideally be KZK type, standard roller cages (K) are not designed for crankshaft use and from my experience will fail prematurely with cage failure. I don't know who manufactures the silver plated cages Eldert posted, but they look correct. I used some old stock Durkopp bearings sourced in Italy (similar looking) some years ago without issue.
Regards Nigel

IKO and INA have some interesting information on motorcycle specific big end caged roller bearings:

http://www.ikont.com/catalogs/needle-ro ... _KT-EG.pdf

https://www.schaeffler.us/remotemedien/ ... _de_en.pdf

A new pin/bearing/thrust washers set could bring your rod back into radial clearance specification if the big end eye isn’t worn beyond the service limit. The problem with the Ducati rods is that the thrust surfaces on the big end wear excessively (usually only one side) so the axial clearance is beyond the service limit.

Matt

Yea, I expect the damage goes beyond the bearing Eldert. I have a machinist friend who may help me. I was thinking of installing a steel insert at the big end of the old con rod. I understand the bearing clearance is critical, and must be done right. I need to disassemble the crank. Unfortunately it is 400 miles away, and I cannot get to it for awhile.

Thanks for the info about the KZK, Nigel. I see there are several choices for the K32x39x18. The KZK version I'm sure is much scarcer. of course the bike manufacturers can get the size they want in big quantities.

Matt, is the bearing you have a KZK?

I'm wondering what Ducati uses the 27-30-27 crankpin on ebay at the link below. The seller claims it is for narrowcase ducati.


https://www.ebay.com/itm/DUCATI-Narrow- ... 0290.m3507


Dave

Hi Dave

seller is the widow of Joe from eurorods . Joe had some Carrillo rods made that used the Husqvarna 30 / 38 /18 mm bearing
Joe had pins made for these bearings . you could resleeve your rod to 38 mm and use this pin and she is selling the bearing to .

pins are OK . i bought some 27 /32 / 27 pins from her .

Eldert

Dave,
The bearings I use are not KZK. The KZK cages are a sheet metal stamping that are designed to retain the needles. The bearing I use has a machined bronze cage. The needles are loose same as the original Ducati big end bearing but the original mass production cage is made of aluminum.

Matt

KZK bearings cages are machined from steel and hardened and tempered for high strength, unlike standard needle rollers cages that are pressed. KZK cages have retained rollers, although many OE specific rod bearings have loose rollers.

On another note, side thrusting mostly occurs due to poor geometry of components and poor rod design. Using Bronze side shims and a better fit of the shims to the pin helps reduce wear and protects the crank.

Nigel

I didn't know that steel cages are being used for big end bearings.
There was a time when only light alloy was seen for this application.
Can we assume that there is now no advantage to using light alloy instead of steel?

As far as know steel cages have been used since the sixties by many manufactures, possibly earlier. Alloy cages are traditional and as you say are light and have worked well over the years. The issue with alloy cages is strength especially with high rev race use where the cages can fracture and fail. that said for many applications an alloy cage can provide good service. The problem is manufacturing cages in alloy for small batches is expensive and nowadays it makes more sense to go with what's available, be that a std KZK bearing (INA, NTN, KOYO...) or from another available bike manufacturer (Yamaha, Honda....) The only advantage of using an alloy cage in our application is in size as 32/39/18 is not normally a std size, however Elderts picture indicates there is a solution available. I have considered having some alloy cages manufactured, but if there is a source of suitable steel cages then it seems a little pointless. The other issue is that many/most original rods are unserviceable and the situation is only getting worse as time goes by. In the case of manufacturing new rods or sleeving existing rods it makes no sense to use the 32/39/18 bearing as the 30/38/18 size is manufactured and used by so many recent and current manufacturers. I've used the 30/38/18 bearing in 450 based race singles up to 493cc with very good life, one lasting 10 years of racing including 9 Manx Grand Prix/Classic TT's. So in my opinion it is more than adequate for any road single. Larger bearings if used with well toleranced parts in a good engine build should be near indestructible. I have one crank in a race bike with a 34/42/20 yamaha bearing and rod which dates back around 15 years. Ducati made the bearings bigger in latter years, but poor manufacture/inspection, tight clearances and double row rollers saw little or no improvement in life.

Nigel

Thanks for the update, Nigel.

Right, K: stamped sheet metal cages, KZK, machined steel. Lost my bearings for a moment there…

The alloy cages in the standard Ducati rod seem to hold up OK but I’ve seen one or two in very loose rods that broke up.

The Mach 1S crankshaft uses a bronze cage.

It has occurred to me that sleeving a rod has the potential to weaken the rod since the section is thinner in order to accommodate the sleeve. Also, I remember Eldert posting on this site a picture of a Carillo rod where the sleeve had rotated, blocking the oiling relief on the thrust surface of the rod.

I had the occasion to disassemble a Ducati 160/125 crankshaft and a Bronco recently. These two models use the same rod. The big end bearing appeared to be the K type, (stamped sheet metal cage) rather than the alloy cage used in the bigger singles. Perhaps with the lower output of these models a K type bearing is adequate.

Matt