Gudgeon pin bushes or bearings

C

chris78jota

Senior member
Location
England
All the two stroke engines I've stripped have had needle roller little end bearings, whereas I can only remember seeing four stroke engines with plain/bronze bushed  little ends.

I was wondering if any of our engine experts know if this is set in stone, or if there are any notable exceptions and what the pros and cons are?

Cheers
Chris with too much time on his hands to think about "stuff".
 
Bushes rely on a generous amount of lube to survive.  Lots of bushes in 2-strokes back in the days of 25:1 pre-mix.  Needle bearings live happily on just a drop of oil now and then, which is all you get with 100:1.

4-strokes have literally gallons of oil flying around under the piston, no need for needles.  These would also necessitate specially ground and hardened little end eyes in the conrods.

piet
 
If I remember Nortons well enough ... a tapered roller on the drive end and only a small bronze bushing on the other end and has to do with the sideways torque on the crank. It was always the tapered rollers that failed!
 
Thanks chaps, that's made it clearer.

What set me off wondering was the Massimo Clarke article on the 75 and 100 racers from an old bike magazine. Perhaps you came across this Piet when preparing your 100 for the Mi-Ta?

When detailing the engine work that the factory had done to the racers, it showed the ufficiale engines had conrods with the little end bushes removed and which apparently ran on needle roller bearings.

Chris

 
The Benelli 650 Tornado had needle bearings at the con-rod small end. I campaigned one in the then new "650 production" class in the 70s.

3_650Tornado_600xp.jpg


A super short stroke engine with very different pistons...oddly cast domes, AIRC.

Anyways..the Benelli had needle bearings at the gudgeon pins.  They never had any problems in competition.
 
The BDG250H Triumph I am working on currently has bronce bushes in the small end, too. It runs - as Piet pointed out - officially with 1:20, happily survives 1:30, too, though as I was told (which causes less issues on other points, smoke from the exhaust being one). But then this is a fairly low reving engine (peak power at 3.800).
 
Rusty Spokes said:
The Benelli 650 Tornado had needle bearings at the con-rod small end. I campaigned one in the then new "650 production" class in the 70s.

3_650Tornado_600xp.jpg


A super short stroke engine with very different pistons...oddly cast domes, AIRC.

Anyways..the Benelli had needle bearings at the gudgeon pins.  They never had any problems in competition.
Click to expand...

What's that massive flywheel in between to four crank webs?? Looks like a BSA crank in the middle of a Laverda SF crank! Must have weighed a ton.
 
Piranha Brother 2 said:
What's that massive flywheel in between to four crank webs?? Looks like a BSA crank in the middle of a Laverda SF crank! Must have weighed a ton.
Click to expand...

Possibly not a flywheel, but a retainer for the centre crankshaft bearing?

bazzee
 
I think that lump is the flywheel not a retainer..it has been a few decades. The engine was not fast rev-ing and was an interesting design. 84mm bore and a 58mm stroke. Short push rods and really not very powerful. Very difficult to tune for more power too. Did okay (not great) against other 650 class machines..BSA and Triumphs as many of those DNF'ed.
 
chris78jota said:
Thanks chaps, that's made it clearer.

What set me off wondering was the Massimo Clarke article on the 75 and 100 racers from an old bike magazine. Perhaps you came across this Piet when preparing your 100 for the Mi-Ta?

When detailing the engine work that the factory had done to the racers, it showed the ufficiale engines had conrods with the little end bushes removed and which apparently ran on needle roller bearings.

Chris
Click to expand...

The needle bearings were probably fitted for friction reduction, every little thing adds up when you want to extract the maximum from such a small engine.

No worries with the stock bush in my tiddler.  Just very basic tuning mods on the Mi-Ta 100, proved to be pretty quick!

Guessing the short-stroke Benelli crank simply did not offer enough of the flywheel effect that would  have been expected of such an engine, hence the additional central flywheel.  Italian manufacturers often added external flywheels, mainly to keep crankcases small and crank bearings close together, bit dated by the time the Tornado appeared.  Why the Benelli engineers deemed a needle bearing small end necessary escapes me.

piet
 
Only just seen this. I can add a little to the Benelli info.

I've rebuilt - for racing - A couple of Benelli singles and one 650 twin. The gudgeons on the twin when stripped were badly grooved where the needle rollers ran so new pins and bronze bushes went in. Talking to a guy who'd worked in the Auckland agent's shop, he told me that failure of the needle rollers was quite common to the point where they were replacing them with bronze bushes under warranty. Doing the job so he said with the engine still in the frame.

The crank on the twin does indeed have a central flywheel. At least it made it easy to change the balance factor. Which was badly needed. It shook like a wet dog and shed silencers on the track. At 80% it was fine.
Seeing a single crank alongside the twin, I reckon the end forgings on the twin are the same as the singles. Common short stroke hence the very large bore of the 650.
The outlet from the bypass oil filter comes up directly under the central flywheel....

The singles use rockers which are both 1:1 ratio. The twin uses the same exhaust rocker at 1:1 but the inlet is from memory around 1.3:1. Aermacchi N6 profiles went into the twin and worked very well indeed. It finished up about as quick as a well worked 650 Triumph.

I've personally never struck another fourstroke engine with needle roller small ends.
 
IF I remember correctly, Benelli split into Benelli and MotoBi in the fifties (family dispute between brothers) but both stayed in Pesaro.

MotoBi employed the great Primo Zanzani to develop their engines for racing, which he did very successfully. (bear with me, I'll get to the point eventually  ???)

Eventually, the two brands merged again in the sixties under the Benelli banner.

My (left-field and totally unsupported by fact) hypothesis is; could Primo Zanzani have influenced Benelli engine design culture? 
Primo was a very talented racer and engineer, who raced a Laverda 75 and often beat the factory's own bikes - so much so that he was taken on by Francesco Laverda in the Laverda race workshop to develop the ufficiali racers. That development work transformed the speed and reliability of the Laverda racers, which included adopting the needle roller little ends.

It is credible to believe that, when later working in the Benelli racing department in the early sixties, Primo used some of the tricks learned on the Laverda tiddlers on the Benellis - and is it possible (big leap of faith) that Benelli used needle roller little ends in their high performance bikes as a trickle-down from the racers?

After leaving Benelli, Primo opened his own workshop in Pesaro, making MotoBi race bikes. He again had the foresight to be an early adopter of disc brakes on racing bikes, and developed plasma-sprayed aluminium discs which won 24 world championships...
Sadly Primo isn't with us anymore, but his family still run the family business and are rightly proud of their father's skills and innovation.

:D I've no facts to support the suggestion of course, but its fun to consider such things. I'm sure Primo could have told us the reason, and many other great stories about the fifties and sixties Italian motorcycle industry.
 
There was ceertainly a lot of crossover within the Italian industry.

Someone commented on the odd heads on the 650 twin. When I saw them first, I recognised them as very similar to early Pantah heads. By that time I was very familiar with those bloody things and knew how to make them breathe a bit better.

They've even got the very short valves typical of Ducatis of that period.
 
I dont recall the cylinder heads. I do recall the odd castings for the piston crowns. Looked like a mountains/valleys in Tora Bora. Definitely not a flat top piston. The machinist said to forget about making horsepower..just have fun.

Did not have any problems with the needle bearings in the con rod small ends. The bike was ridden on the street very little so it did not get a lot of miles. The needle bearings were replaced every time the top end was disassembled, a two stroke engine best-practice.

The machine shop did shorten the already short pushrods and removed a equal amount from the rocker arm support platforms. Due to the separation/difference angle vs straight line of the cam to rocker ends..this increased the overall lift of the valves.

Seems like we used some BSA/Triumph performance valve springs and maybe retainers too. Definitely not Benelli valve springs.

I recall the piston squish was ridiculously huge. Tightened up to a performance clearance helped with the power and increased the compression ratio.

At the end of the day the engine was reliable but too heavy a motorcycle to be really competitive long term.

Indeed the engine was an odd ball design. And it was fun too.
 
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