Restoring LeMans III engine . 850 to 950 and other stuff.

[Max1000sp]

I am sticking my neck out here but would like some opinions and experiences.
I  am currently tearing a well worn LMIII engine apart, planning to give it a new life, unless I stumble across something really bad like cracks in the case.
One of many nescessities will be buying new pistons and cylinders.
Since I will be using the engine in a 1000SP, I per refleks thought of 1000 cylinders = 949ccm.
There are kits with special pistons made for LMIII heads.

But apart from going original, what are the pros and cons of 850 vs 950?

[Max1000sp]

Stripped to the backbone   



No warnings against bigger size?
I’ll go for the bigger bore then, hoping for a nice torque. Also because the bike is occasionally used for touring.
Rosso Mandello clutch should be a good “not too heavy, not too light” fit  I have been happy with it on the SP engine.

[oldbike54]

 Don't think you'll find any resistance to the 949 displacement on WG , sounds like a great project 

 Dusty

[Antietam Classic Cycle]

I'd definitely recommend balancing the crank - the 88 mm pistons are likely heavier than the 83s they replace. Even if they aren't, the factory didn't always balance these engines that well.

[fotoguzzi]

I thought many people say the 850 is a perfectly balance motor and the 950 has more vibration?

[Cdn850T5NT]

Heard that too...

[pete roper]

If they are available I’d try to get a kit for an SPIII. These had mid valve heads same as the MkIII LeMans but a 949 capacity and a slightly lower compression ratio. Balance the crank, rods and piston assemblies and stick with LeMans advance springs and a pair of ‘Lean burn’ 36mm PHF’s and you’ll have one of the sweetest motors money can buy.

[Max1000sp]

Thank you all for your input.
The original question regarding 949ccm vs 844ccm seems solved.

I was leaning towards only balancing the crankshaft assembly in case the new pistons weigh different than the old.
But is it enough to have shaft, rods and pistons assembled (with the used rod-bolts)? How about the flywheel? Which I don’t have a spare of...yet.

Interesting alternative with the SPIII kit, which I take is cylinder-piston with lower compression than the LM.
But I went for a LeMans engine to try that out compared to the SP, and got one with 2 spark plugs/top, almost new coils (Silent Hektik) and external oilfilter. The latter I’ll try out, as I can easily go back.



More project details: I got the 36mm PHFs, DynaIII ignition (and the old point-ignition in reserve), aluminum timing gears (Which looked great at last view) and as mentioned a Rosso Mandello clutch. These parts are currently mounted on the SP. Oh, and a Valeo starter to cope with higher compression.

I am not looking for an all-the-way race bike, but a fun reliable street bike able to do a few longer tours on.


 
And again. Get to try the feeling of a LeMans engine for a longer period of time.

Thanks again for your views. Balancing will be on my list now, if it makes sence with just shaft, rod and pistons.

[stubbie]

I have the big bore kit in my latest Le Mans but I think my 850 had more go in it. I did have 15 years hiatus in between these 2 bikes so my memory of the ride might be distorted and this bike was rebuilt by the previous owner so I'm a bit reluctant to fang it in case something gives way.

[pete roper]

Ditch the timing gears, they're a ticking time bomb.