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Hi All,
Ok, so the cause of the fried stator was the main bearing going west, only reason I can find is the rubber connector between oil pump and clutch cover being knocked off during assembly (it was laying in the bottom of the clutch cover). Amazingly, the big ends were/are still ok and oily. (can only assume enough oil was getting to the big ends, but not enough pressure to flow against centrifugal force to get to the main.) Rebuilding with the crank and generator from my Strada means I’m back on the road and all seems ok so far.
So my question is thus: So that I can rebuild my Strada engine, should I simply grind crank to next undersize and fit another plain bearing or grind the crank further like some have done and fit a ball or roller bearing? (6206 or NJ206)
From the latter option, the way I see it is that a roller would be better as it wouldn’t need the sleeve on the crank to allow for expansion like the series 1 bikes had and If the roller/ball bearing option is really the best way, how have people gone about blanking off the oil drilling in the crank? Is it simply a longer gallery plug in the crank? Welding?
My mind says stay plain – after all, the original bearing lasted over 90,000miles without issues before, but I’m an Engineer so can see benefits with the ball /roller mod. If it is truly beneficial, now is the time to do it while it is in pieces and the crank needs grinding anyway. I should add that the bike isn’t going to be track day’d .
Machining costs are not a consideration as I can get that done for free and the prices of a roller bearing or a plain bearing are very similar.
Your deliberations please.
Thanks,
George.

The way I see it, the plain bearing is a weakness in the engine design, which in itself was chosen as a result of a weakness in the ball bearing of the series 1.

The roller bearing conversion will give you a better oil supply to the big ends as you will have got rid of the plain main. It won't fail like the plain bearing does and so reduces the chance of wrecking a generator. The plain bearings are known to corrode if the engine is left standing for a period (beware anyone who buys a morini which has been dormant for years- check the play in the timing side bearing regularly during the first couple of thousand miles and you may just detect the beginnings of the bearing failing and save an even bigger repair bill)- I don't believe the same failure would happen for the roller mod. The roller bearing might give you more revs (difficult to verify!).

It's not all good news- there is a chance you could introduce problems if the blanked off gallery fails or if the plain bearing/crankcase bolt holes don't seal- but both of these are easily prevented with good engineering. I plugged the gallery in my 501 with an interference fit ally peg which is partially shielded by the roller bearing anyway so shouldn't come out. I had the 3 holes in the crankcase for the plain bearing housing welded up. No issues with mine in a good number of miles of thraping!

To my mind it is a neutral cost update which should improve things and if done properly won't give any problems, so it's well worthwhile. I also took the opportunity to have my 501 crank lightened and balanced while the journal was being ground. Part of my decision to do the timing side bearing on the 501 is that the clutch side bearing in the 500 is a morini-special obsolete bearing which is in very short supply so I wanted to do everything possible to prolong my engine life so I didnt have to source another bearing anytime soon (we'll ignore the life reduction caused by the lightening, camshaft, carbs etc!)

I'm a big beliver in KISS, keep it simple stupid.

I've rebuilt big diesels, like MTU 8V392's. That means that each piston has a displacement of 3.92 litres. They use shell bearings on the big ends with compression ratios that would blow the sides out of a Morini barrel.

I've also read that some Morini big end shells are the same as Mitsubishi cam shells. If so they should be cost effective.

Up to you, grind the crankshaft more than needed but it isn't what I would do. Pros and cons.

Just my take on it but I am a heretic rather than a believer.

Rod

Morizzi wrote:I've rebuilt big diesels, like MTU 8V392's. That means that each piston has a displacement of 3.92 litres. They use shell bearings on the big ends with compression ratios that would blow the sides out of a Morini barrel.

What do big end shells have to do with the timing side main?

I've also read that some Morini big end shells are the same as Mitsubishi cam shells. If so they should be cost effective.

Assuming they're the right dimensions, what is the material? The OEM shells are white metal that is tollerant of dirt (no filter of course). NLM have plenty of shells these days and they're not excessively expensive.

Up to you, grind the crankshaft more than needed but it isn't what I would do. Pros and cons.

Morini went to the plain bearing to solve potential problems (at around 40,000+ miles I believe) with the ball race timing side crank bearing. They used a hardened steel sleeve on the crank that was designed to slide in the bearing to accommodate expansion. That meant that they had to hold a very fine tollerance for the fit of the sleeve on the crank and the fit of the sleeve in the bearing. The sleeves would sometimes fret on the crank, or fail to slide properly in the bearing. The plain main bearing would have been a much cheaper fix than using a roller bearing, so that's what they did. If NLM have an early engine apart, they automatically upgrade the timing side main from a ball race to the roller as it's pretty much a drop in job. Morini never tuned the 500 to even the level of the Strada engine (100bhp per litre) and I think it's probably becuase the plain main bearing that was considered marginal for the increased loadings from the longer stroke 500.

The roller bearing conversion is a well known performance upgrade. You're really only converting the crank back to the early specification although the journal is actually bigger because you don't need the sleeve.

My own 350 is a stock (as far as I know) plain bearing engine and I'm pulling as much as 10,000rpm at Cadwell with no signs of any problems. If I was doing a major rebuild, or tuning an engine I'd probably do the roller conversion as a matter of course.

The plain bearing engine may be a little quieter due to the damping effect of the oil, but unless it's a Gilardoni barreled engine, then you're unlikely to notice.

on the later sport engine what is the size of timing side crank journal from standard, and what is the minimum and max clearance between journal and plain bearing , the later engine uses 3 allen bolts to locate the bearing carrier, inside that is the plain bush , hope iam not confusing you all , in which sits the crank journal , thats the clearance spec iam after, i think ive lost the plot, i dont think it i know it. muller.