Plain bearing big ends

[Lumpy]

I was recently offered a tired old bevel motor. She`s a re-builder and started doing a few sums as to what it would all roughly cost to breath new life into her. While trawling ebay I saw a Darmah for sale that claimed to have Carillo rods in her. I thought thats an option for the big end so I emailed and asked for a price. Was pleasantly surprised with normal rods going at USD$319. Carillo I understand are at the top of their game when it comes to connecting rods. What really got me thinking was that they also make a plain bearing rod for our Duc`s. Cost of USD$378. You suss out a bearing, no doubt cross reference a toyota or similar bearing and Bob`s your mums brother. They may even have a suggestion as to what bearing would suffice. Now I don`t know about the rest of you but give me a plain bearing over this roller buisness anyday. Easy and cheap to replace, robust, simple. A million engine manufacturers can`t be wrong.
My question is to all you Bevelheads out there, has anyone heard of this conversion being done. Obviously the oil pump and bypass valve have to be replaced/modified. Possibly filter assembly. Wonder how all the rest of the oil drillings would take to the change in pressure/volume. I know it`s been done before. In the musty archives of my memory i remember a guy racing a bevel twin who finally cracked the sh*t`s with the fragile big end and converted it over. Who or where he was I can`t remember but do remember the article was very light on in detail. I also remember he was very pleased with the results and the thing was thrashed relentlesly there after without incident. Just a thought...................

[wdietz186]

Lumpy, I think that guy you are refering to is an old bevel racer in California named Kevin Bracken. He has written a series of articles on how he developed his racebike.I think it is on this site somewhere in the archives. The short answer is yes it can be done,the somewhat longer answer is it's a lot of specialist work and nowdays likely to be pretty expensive. OR if you can find one the late Mille engine has it all done for you. A pair of Carrillo rods ,a well assembled crank, and a fresh oil pump should be sufficent to handle the thrashing any well heeled sympathetic owner who pays the bills would dish out.

[machten]

I've got an article from an Australian 1994 Streetbike magazine that describes what was required to fit Mille shell bearings into 74 750 Sport when it was restored in about 1994 by Cafe Racer Motorcycles of Melbourne. Besides what had to be done to the crank and rods (as he wanted to use the Sport's rods to retain the its theoretically perfect 2:1 rod/stroke ratio), they describe using...

"... a modified Mille oil pump (with specially wound springs to incorporate an oil pressure relief valve) providing 90 psi pressure via a 900 oil pump gear. "

and also..

"...Oil flow to the heads has been restricted to allow more oil to the crank"

They did have to tap into an oil way too, but apparently it was exactly what existed in an 860 anyway.

Seems like a lot of work unless you're going to ride big miles each year. PM me if you want a copy of the article.

[Kickaha]

Now I don`t know about the rest of you but give me a plain bearing over this roller buisness anyday. Easy and cheap to replace, robust, simple. A million engine manufacturers can`t be wrong.

I've alway wondered just why Ducati roller bearing bottom ends seem so fragile when the old GSX series Suzuki roller bottom ends used to last for ever (slight exaggeration) and were so popular as drag race engines due to the strong bottom end

[Lumpy]

I know what your saying. Many manufactures have made rock solid roller big ends, unfortunatly the objects of my obsession did`nt. Some of the reasons for the Ducati failures I`ve heard are uneven cooling of the rods after heat treatment due to non uniform thickness around the rod, the one step advance of the Electronica ignition, not being pedantic about your oil changes, using wrong oil that made the rollers slide instead of roll, plugged sludge traps and I`m sure there are a few more out there. If I went that way, and I`m still very dubious as to whether I will, I beleive with a plain brg big end, a decent ignition system and maybe just maybe one of those Vee Two gear boxes, although those little puppies are expensive, I rekon you`d have a Duc motor you could put up against a BMW boxer for reliability and milage and still stand up to p*ss(just kidding all you BMW owners, no hate mail please). Obviously they have to be maintaned a little more fastidiously with Desmo`s but in my humble opinion if there is one thing I`ve learned over my years of ownership, when a bevel goes Ka-bloowee it`s one of those components at the root of it. This motor I may be able to access would be a project and would`nt leave me putting cards on the spokes of my mountain bike to get my Duc fix. It would be long term, I have access to machinery and do all labour myself so it`s all just parts. Added to that I could flog off the original ignition and gear box components to offset some of the cost provided they`re salvagable. Just kicking ideas around, thanks for the responses.

[Craig in France]

I've alway wondered just why Ducati roller bearing bottom ends seem so fragile when the old GSX series Suzuki roller bottom ends used to last for ever (slight exaggeration) and were so popular as drag race engines due to the strong bottom end

I've never heard a truly convincing explanation either (perhaps comparing a V-twin with an in-line 4 isn't quite fair , but even so ... what do Vincents run, for example?)

I understand that the basic mechanical cause is wear in the thrust washers which allows the con rods to tip and the bearing cage to catch the crank pin. But why the thrust washers should fail, and why some engines seem to run for miles and others blow up at a young age, I do not know. It could, of course, be something as basic as the relative quality of the original assembly, one crank against another - which, if true, would defy any attempt at forensic analysis, unfortunately.

Anyone got any better info on this?

Ciao

Craig

P.s. Zané Laverdas also throw big-ends - and, again, the postulated reasons are many, but no-one has yet come up with the definitive answer.

[Vince]

Craig last I heard Piet and the Oct blokes in Germany came to the conclusion that someone left a decimal point out in the bigend spec,re the Zane bikes,some came new with way too much clearance,that was on the Laverdapedia site zane discussion a couple of weeks back,who knows,what with the watch like setup of a bevel maybe there was some Friday after lunch assemble on some bikes.

[Lumpy]

I believe Brook Henry at Vee Two used to remanufacture the Duc big end by inserting hardened sleeves into the rods. I`m not sure if they still go that way or what the sucess rate with them was. That would suggest to me that there was a issue with uniform hardness around the conecting rod eye. I guess the other thing with comparing a GSX with the Duc is the GSX`s were 1000cc divided by 4 so only 250cc punching down on each rod. Added to that a flater torque curve of the Duc`s. I know Harley used to run rollers waaaay back when (had an old WLA motor laying around once) but they don`t spin anywhere near as hard although do have an impressive torque curve. Does anyone out there know of a Bosch ignition Duc big end failure?? Just wondering if the more progressive ignition advance curve of the Bosch helped out at all. I certainly know they seem to pull a lot smoother through the rev range. All big end failures I`ve known were on Electronica equiped engines but thats not to say some of the later ones did`nt let go as well. I just have`nt heard of them. It`s also worth noting that big two stroke outboard motors use rollers and these are lubed by thin as water two stroke oil and very sparingly at that and they seem to go for ever (well...until the oil feed to them stops) with serious horsepower punching down on them. Duc big ends get thick 50 weight oil and plenty of it.

[Craig in France]

I believe Brook Henry at Vee Two used to remanufacture the Duc big end by inserting hardened sleeves into the rods. I`m not sure if they still go that way or what the sucess rate with them was. That would suggest to me that there was a issue with uniform hardness around the conecting rod eye..

This repair is done in the UK too, but normally 'cos the rod eyes are cream-crackered when the big end goes. Sometimes works, but I also know of a number of cases when it hasn't. Don't know why.

I guess the other thing with comparing a GSX with the Duc is the GSX`s were 1000cc divided by 4 so only 250cc punching down on each rod. Added to that a flater torque curve of the Duc`s. I know Harley used to run rollers waaaay back when (had an old WLA motor laying around once) but they don`t spin anywhere near as hard although do have an impressive torque curve..

Agree on both scores. Still doesn't explain why Phil Vincent could build a motor that didn't destroy its big ends - assuming they were rollers, of course ...

Does anyone out there know of a Bosch ignition Duc big end failure?? Just wondering if the more progressive ignition advance curve of the Bosch helped out at all. I certainly know they seem to pull a lot smoother through the rev range. All big end failures I`ve known were on Electronica equiped engines but thats not to say some of the later ones did`nt let go as well. ..

Don't know. But also, the Darmah engine had a re-designed big-end, anyways ..

It`s also worth noting that big two stroke outboard motors use rollers and these are lubed by thin as water two stroke oil and very sparingly at that and they seem to go for ever (well...until the oil feed to them stops) with serious horsepower punching down on them. Duc big ends get thick 50 weight oil and plenty of it.

I'm not persuaded it's as simple as an oil weight issue, even if Ducati did change their oil spec to 10-40

Ciao

Craig

[Lumpy]

I guess as far as the oil weight issue goes I`m trying to say that in my mind the Duc big end should be better equiped to handle whats thrown at them due to more lubricant flowing through it and that lube being more viscous, when you look at it against an outboard. I would have thought that a heavier oil would be more protective of the rollers and rods. Interesting about the re-sleeved rods you guys get over there. I never got to hear any feed back regarding the ones Vee Two were doing. I`m not sure on this one but I think the later big-ends benefited from a larger crank pin. Larger crank pin means more rollers and more rollers mean the load is distributed with less load on each roller. But as you and others have pointed out Mr Irving made that delightful big angry Vincent twin that as far as I know could`nt be destroyed with a sledge hammer. Wonder how the helical cut primary drive effects the whole set up. Helical gears will give off a side thrust under load but I`m not sure which way the gears are cut and which way the load goes. I know of a straight cut primary set up available but it`s mega bucks. You`d like to think they would have had the load pulling against the angular contact main bearing thereby not pushing against the crank and causing it to flex. I was sniffing around a Laverda site a ways back and I see they make belt drive primary drive for those..........hmmmm, I wonder.......nah, just getting silly now!!!

[MartinMille BANNED]

Are you guys talking about Needle roller bearing or Ball roller bearings ?

[Kickaha]

I believe Brook Henry at Vee Two used to remanufacture the Duc big end by inserting hardened sleeves into the rods. I`m not sure if they still go that way or what the sucess rate with them was. .

I know I had a Vee Two bottom end fail 11,000km after it was fitted in my Darmah about 1992-93, the report we had done on it suggest insufficent hardening on the crankpin was the cause

They replaced it even though it was outside warranty (10,000km) but I still had the wear the labour cost to have it done over here

XS650 Yamaha is a twin cylinder roller bearing bottom end and they have a reputation for reliability even with the big bore kits fitted for racing

[machten]

The crank modifications made for the Bosch ignition Darmah supposedly significanly improved the situation over the 860's. This was incorporated into the the SS in 78. One of my Darmah's is at 87,000km with no discernable bottom end noise (yet!). On the other hand, I'm at near valve shim limits and need to look at rebuilding the heads. My reading over the years has indicated the following:

1. the aggresive timing advance profile of the ducati electronica ignition was a contributing factor in early crank failure. The Bosch four step advance provided a more gentle change. (But try synching carbs based on vacuum advance at while you try to hold 2800 revs!!)

2. The crank pin increased to 38mm with 23 caged needle bearings (from 36mm).

I have a 78 darmah with 59000km that I've owned since near new. I rebuilt the gearbox at 43,000, but the big end wasn't touched as it didn't seem necessary. It still sounds fine (I may regret saying this!!)

I've always changed my straight 50 weight oil between 1500 and 2000km and my filter every 2 oil changes. It's worked for me, anyway.

Kev

[stanley]

Biggest factor is oil used I have seen, the other is over revving.
Mike Soderlands Darmah ran for a good few seasons on the crank it was fitted with when 1st built, he was gentle on the engine (but real fast- attested to by anyone who watched) & never revved the snot out of it.
Frequent oil changes is also a big bonus to preserving the cranks. I always use either Castrol or Motul 50w, no multi grades.
The later big-ends were a step up from the 36mm big ends but you can fit a stepped 36 to 38mm big end assy. or have your crank shaft bored to suit. You can also have the hole offset bored to give a bigger stroke.

My '75 SS was still running the original big end when I pulled it down due to noisy gearbox issues. We split the crank, all was fine then re-assembled it with new rollers. Cant remember exact km's bit it was well used.
My father in law has a '78 SS that has covered about 360,000km with 3 big-ends being thrown into it over those km's but it has been raced, thrashed, crashed etc. since 1980 with him so not a bad effort.
When I worked at Gowies we had a 900S2 with 230,000km's on the original big end. We pulled it down eventually & just replaced the rollers also as nothing was worn. Lost track of the guy now but I would think he still has it.

Dave Ward
Moto Italia
Aprilia-Ducati-Moto Guzzi
0432 441 985

[wdietz186]

The article I mentioned in an earlier post is on this site. Go to articles index and scroll down to Kevins Bevel Article. It is full of good info about cranks and other stuff.