850 LeMans MkI Barrels on 850T

[swooshdave]

Friend of mine is restoring a 77 LeMans and is going to put new barrels on it. I asked him what he was going to do with the original barrels and he said either make an art project out of them or put them on the shelf to gather dust.

What would it take to put those on my 850T? I would get the pistons and barrels for a VERY good price. Just bolt on with fresh rings?

Side question: Are the Gilardoni barrels marked on the inside? I recall someone mentioning seeing them stamped.

[Cam3512]

So a "friend" has no use for them other than dust collecting art.  Yet, you have to BUY them from him?

Gilardonis are stamped at the very bottom of the cylinder, facing out.

I do use my old /5 jugs as bookends on a shelf in my garage.

[PeteS]

How many miles on the LeMans? The jugs have iron liners and may need to be bored if worn. Also I think the pistons are different anf may not work with the T heads. Someone else will have to verify that point.
I would want to measure evrything up before dropping any cash.

Pete

[swooshdave]

I guess the Pistons won't work because the LeMans ones are high done?

I said a VERY good price. What is the best price you can think of? ;-)

[Cam3512]

I guess the Pistons won't work because the LeMans ones are high done?

I said a VERY good price. What is the best price you can think of? ;-)

Ahhh, got it.

[swooshdave]

Will the LeMans pistons work with the 850T heads?

[pete roper]

Will the LeMans pistons work with the 850T heads?

No.

[TOMB]

Also take into account that the Valves in the T are a lot smaller in dia than the lemans then you'll need the carbs, and the heads , then you will have to remark the flywheel as the timing marks are in a different location ==== and the list goes on

TOMB

[swooshdave]

Also take into account that the Valves in the T are a lot smaller in dia than the lemans then you'll need the carbs, and the heads , then you will have to remark the flywheel as the timing marks are in a different location ==== and the list goes on

TOMB

For just a barrel swap? Best case is that the 850T pistons fit the LeMans barrels and then isn't it just a ring change?

[guzzista]

Yes, if  your pistons measure within spec of the jugs , it might just need a  light brush hone , new rings and you are good to go.

[pete roper]

Pistons should be cam ground, this will make them under-spec so they will be too small for the barrels.

Or cou could put them in. Have rhem be the wrong shape when hot and either drink copious oil or seize.

[swooshdave]

Pistons should be cam ground, this will make them under-spec so they will be too small for the barrels.

Or cou could put them in. Have rhem be the wrong shape when hot and either drink copious oil or seize.

Are you saying that the 850T pistons are a different shape (circumference) than the LeMans ones?

How exactly would one put the iron barrels on an 850T? New pistions and rings to match a freshly bored barrel?

[pete roper]

Pistons aren't *round*. They're put simply, oval. They are designed this way to deal with thermal expansion and are machined, (Cam ground.) to the required shape.. They also wear in to *Match* the bores they run in.

While you may get lucky and everything may work it will be less than optimum and there is the possibility for seizure or poor sealing as I alluded in the earlier reply.

You can certainly use the barrels, what you would need is oversize pistons so the barrels can be bored. Charlie or one of the other guys may know of a source but since most of the 850's used chrome or Nicasil bores, (The LeMans were an exception. Who knows why?) o/Pistons for small valve heads are not something I know of as being available. Remember though, I haven't been doing much 'Older Stuff' work for ten years or so so I may not be up to snuff on what's available. From memory the walls of the sleve are thick enough to take 88mm pistons, (We used 90mm Wisecos on one iteration of the racebike but that was mid valve heads?) with what I think we're stock LeMans barrels. By the time you've bought prisons and rings, gudgeons and clips etc. though and paid for the reborn you'd have to be close to the cost of a set of Gillardonis?

Pete

[swooshdave]

By the time you've bought prisons and rings, gudgeons and clips etc. though and paid for the reborn you'd have to be close to the cost of a set of Gillardonis?

Pete

That is the wisdom I'm trying to ascertain, is this even feasible? Replating with Nikasal seems more cost effective at $400/or vs. $800/pr for the Gillardonis.

[pete roper]

Sorry, you probably don't need a prison, let alone a pair!

[jacksonracingcomau]

Back in the day was quite common, le mans got big bore nikasil kit. T3 had chrome fall off, barrels got used. Do measure pistons, cast iron needs a little more clearance than nikasil or chrome. Get local engine place to measure if you can't,  hone should be enough, old school engineer will tell you
New rings advisory but seen old work for years, do as budget allows, is only a ditchpump

[Antietam Classic Cycle]

Charlie or one of the other guys may know of a source but since most of the 850's used chrome or Nicasil bores, (The LeMans were an exception. Who knows why?) o/Pistons for small valve heads are not something I know of as being available.

Mark @ Moto Guzzi Classics had pistons made to spec. for both Ambo and Eldos (which would work in a T as well). However, last I saw some for sale they were $600 a pair, totally negating any cost benefit to replating vs. Gilardonis. I know of V700, Ambassador, V7 Sport and 850 Le Mans NOS pistons for sale, but no Eldo/T/T3 pistons.

[jacksonracingcomau]

Mark @ Moto Guzzi Classics had pistons made to spec. for both Ambo and Eldos (which would work in a T as well). However, last I saw some for sale they were $600 a pair, totally negating any cost benefit to replating vs. Gilardonis. I know of V700, Ambassador, V7 Sport and 850 Le Mans NOS pistons for sale, but no Eldo/T/T3 pistons.

Guess I'm missing something here, do we have any reason not to use op's original pistons?

I'd measure them and cast iron lm barrels, then make call,

[swooshdave]

Guess I'm missing something here, do we have any reason not to use op's original pistons?

I'd measure them and cast iron lm barrels, then make call,

That would be option one.

Pretty sure you can't use the rings intended for chrome with the iron bores. So best case is pistons fit and new rings are all that are needed.

[jacksonracingcomau]

That would be option one.

Pretty sure you can't use the rings intended for chrome with the iron bores. So best case is pistons fit and new rings are all that are needed.

Budget/wear on rings only decides this
If you use chrome top ring (cast iron barrel use) on nikasil damage will result
Other way round no issues, soft rings will still seal on cast
New rings better, I recently rebuilt a T3 with cast iron barrels, local bloke matched up some rings along with half a leftover set I'd had for 20 years, seal perfectly but if orig rngs for chrome all I could get, wouldn't sweat, done it many times