Big Bore kit for a 77 Lemans 850 mk1 ?

[vintage53]

Hello Folks, 

I am considering a 950 big bore kit for my Lemans.  Has anyone had any experience with the modification.
Opinions?  .... or better to just keep as Stock.

Would I also need to upgrade the connecting rods?  Any Fueling issues with the Stock Carbs?


Thanks

[blackcat]

I kept mine stock instead of taking the larger bore route. I believe a European supplier is now making the stock barrels in Nikasil.

[acguzzi]

I ran mine like that for many years, a nice torque bump. final about 20 years later I had to replace it because of small end wear and tear and went back to an 850 for race purposes. I would do it again if I wasn't racing it.

[Antietam Classic Cycle]

I kept mine stock instead of taking the larger bore route. I believe a European supplier is now making the stock barrels in Nikasil.

Any more information on this "European supplier"?

[PeteS]

I believe if you get nikasil cylinders you have open the crankcase bores. I did my own but iI have Bridgeport mill. Fairly simple machining operation in any case other than having to pull the motor and take it apart.

Pete

[Turin]

If you want more grunt, change the camshaft to something a little more aggressive like a B10, P3, X9 or SS2. ( all of those are drop in cams and do not require headwork). if it's tired, consider freshening up the motor. (hone the cylinders, new rings, valve job etc.) The stock components are durable enough to hold up to racing conditions.

[Huzo]

I had a Mk2 and probably should have kept it.
Were I you, I would keep it bone stock if it’s relatively healthy. Modified classics are a retrograde step from original equipment.
If your bike is a bit sick (as in unwell), I’d be tempted to renew the cylinders and pistons with 850 components. Even a fast(er) Guzzi is still slow, you’ll gain 10% and lose 75%…..
Anywayyyy…….

[blackcat]

Any more information on this "European supplier"?

I thought HMB was making their own kit for the 850 LeMans, but I’m wrong.  I wonder if the T-3,etc Nikasil cylinders can be used with the stock LeMans pistons and the correct rings?

[PeteS]

It all depends what you are looking. Just a bit more torque or a significant bump in HP. No substitute for cubic inches.
A riding buddy with a built MKIII and 992 kit, cam, Raceco heads, Tolley exhaust could pull Japanese litre 4 cylinders to 100 and 50-100 roll ons. He would still get better mileage than me on my 850 LM. Lot of ponies hiding in there.

Pete

[John Croucher]

Get a lighter clutch assembly and high compression pistons.  Leave bore stock.  Clean up heads, leave rods, valves stock.  The pistons and crank do not need to be perfect balanced, though it does help.  Drill some aluminum out of the bottom of the pistons to get them with in a few grams of the stock pistons. 

I built my 1100 hydro engine with a mix of parts.  Sport 1100 after market hi-comp pistons.  The two pistons are not a match set, two different manufacturers.  I drilled some aluminum out of the bottom of each piston to lighten and match the weight between the two. I did have to work on the squish band since the stock head combustion chamber is smaller.  This removed some weight from the piston.   The heads are small valve used on most California EV's.  Stock hydro cam and lifters.  Running original FI map.  Exhaust is two into one.  Replaced steel clutch with a Ram aluminum.  The engine revs very quickly, has lots of power and is very fun to ride.  I abuse it intentionally every time I ride it.  If it breaks, I had fun doing it and will repair it. 

[Huzo]

What is the perceived benefit in lightening the flywheel ?

[PeteS]

What is the perceived benefit in lightening the flywheel ?

Engine winds up considerably faster.

Pete

[Huzo]

Engine winds up considerably faster.

Pete

Is that a good thing ?

[Guzzistajohn]

Is that a good thing ?

Some think so, yes.

I personally don't like it on a Guzzi but it made one HELL of a difference on a Yamaha TY250 trials bike I once had. 

[Frenchfrog]

Any more information on this "European supplier"?

 Stein Dinse were selling them but doesn't list them at the moment.
Provenance was from an outfit in Spain but the name escapes me...never heard of them previously either but they have a large modern facility near Barcelona.

[testa_di_formaggio]

Drop in 88mm piston/cylinder sets for 850 LeMans and LeMans II are available at SD, should be Stateside shortly.

TdF

[blackcat]

Stein Dinse were selling them but doesn't list them at the moment.
Provenance was from an outfit in Spain but the name escapes me...never heard of them previously either but they have a large modern facility near Barcelona.

HMB now shows them on their website. I have one in my CX from Ed Milich, I think he wants something like $600 bucks for a lightened flywheel.

[Frenchfrog]

The T3 ones...not Le mans. I dont see why one couldn't change the pistons in the T3 set for LM higher compression ones as long as the right rings are used and the clearance measurements work out right too.But then the LM pistons are virtually inobtanium  as NOS. The Spaniards must have had a source for them and maybe that's used up.Hopefully they would be the same weight as the originals too....

[Turin]

BTW, a set of Carrillo rods will set you back about a thousand $. Here are some parts porn pics from my current project. Carrillos are not necessary, but a good friend of mine gave me a deal on them. I'm building something stupid.






.

[steven c]

 I put a Ram Clutch in my 77 that I just sold,I really liked it,made the bike more playful. Then I would ride the With it's man hole cover fly wheel, great for going slow and just heading down the road.

[Gliderjohn]

For everyday riding I have been very happy with this setup on my T-3.

Big bore kit
36mm round slide carbs
V-7 sport cam.
Heavy duty valve springs
Heads polished and ported to match the carbs
Cheap EMGO mufflers.
 


gif guerra

GliderJohn

[Moparnut72]

What caused the big dip just over 3,000 rpm?
kk

[Gliderjohn]

Intentional by the operator for some reason.

[Stretch]

I abuse it intentionally every time I ride it.  If it breaks, I had fun doing it and will repair it.

That put a grin on my face this morning!   
Definitely the right spirit.....

                                     -Stretch

[Dukedesmo]

I fitted a big bore (950) kit to my LM2 after the pistons hit the exhaust valves and I was unable to source new, 850cc pistons (the cylinders were still perfect).


I got the kit from HMB in Germany with the LeMans spec pistons and it was a drop-in kit with no machining required (I understand some need the cylinders turning down or the crankcases opening up).


Can't really comment on the difference as I had little experience of it as an 850 due to the piston/valve incident happening just 500 miles into my ownership. As I had it all apart, I also replaced the valve guides, recut the seats, replaced a loose rod end bush, fitted new bearing shells etc. and it is a strong, well running engine.

[blackcat]

Guess I better hang on to the two NOS LM pistons in my stash of parts.

[Dukedesmo]

Probably wise (unless you want to sell them to me  )


When I was getting the valve guides replaced, I was advised to tread carefully as the heads might crack whilst bashing the old ones out and replacement LM heads are unobtanium, so I opted for k-lining them which is far less invasive.

[moto-uno]

  The 'K' lining of valve guides is a god send . Installed 90mm Wiseco pistons decades ago on my Le Mans 2 . Had LA sleeve company make me some
thicker sleeves which required boring out the cases and had some copper head and base gaskets made for it also . The improvement in roll on torque was
satisfying . The flywheel was lightened by Rennsport in California at least 3 1/2 decades ago and I loved the near instant throttle response and quicker shifting.
The big bore kit had one small negative side affect and that was vibration that quite literally didn't exist when stock. Installed the B-10 cam originally and
felt it should've been a stock cam ( too mild) , replaced it with Mega Cycle 620 cam ( likes being wound out) , and of course 40mm carbs to keep me screwing
around with jetting . Still have the large bore BUB headers on it . Today I'd consider most of these mods an excuse to spend an inheritance :) . Peter