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850 GT Gilardonis

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abitloopy View Drop Down
Guzzino
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    Posted: 07 Nov 2019 at 08:38
I have an 850 GT project that I am about to start work on. It has stood for many years and I am sure that it will need new barrels.

The price of 950 cc Gilardonis is quite a bit less than the 850 cc variants. Would they fit without any other modification needed? I have read that there may need to be some filing done in the pushrod tunnels and also that later rocker gear may be needed, but some clarification would be helpful.
Would it be necessary to relieve the crankcase mouths to accept the larger barrels?

Also, probably more important, how would the bike feel with a 950 conversion? Would any extra torque also make for a lumpier engine?

Allan.



Allan
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 09:18
I believe you are right about the need for later rocker gear etc.
A friend of mine fitted 950 barrels to his T3 but soon reverted to the original 850's.Apparently vibration was a problem. It may also be of some relevance that the 850GT has no rubber shock absorber in the rear wheel and the smaller U/J, so the extra torque might bring with it some accelerated wear issues.
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

1971 V7 Special. 1972 850GT.
1970 T120 Bonnie. 2009 500 Bullet.
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Chris A View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris A Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 12:18
I did the conversion to a T3 and it did vibrate more ...not that bad though...didn't really notice ant difference in the performance.Ideally i would get the crank re-balanced but that comes at a cost
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ranton_rambler View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 12:39
Your barrels may be OK. My 850GT has done 50,000 miles on its originals.
Ian
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jpc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpc Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 12:55
Ditto Chris A as to a T3 conversion.
I found reducing the initial advance from 2° to zero cured the vibration without loss of perf.
Fitting in the crankcase mouths required just a fraction of a mm skimming of the cyl. spigots.
I found the Gilardonis immensely durable, now 200.000 km, which I credit in part to that
godawful Wink original airbox & filter .
Dave P. knows best about loops, but they do have the gearbox spring shock absorber, I think ?
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 13:48
Hi jpc. you are right about the shock absorber in the gearbox and it seems to work well. But Guzzi saw the need to put another in the rear wheel to extend drive train life and I believe that it does. I think where Loops are concerned extra care to match engine speeds with road speed helps to minimize shock loadings on the transmission.My view is, don't lug them, let them rev' and don't change down at too high a road speed to induce engine braking.I'm sure that other opinions are available.
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

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1970 T120 Bonnie. 2009 500 Bullet.
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Amboman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Amboman Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 14:09
Another thing that hasn't been mentioned is head gaskets, as in, there isn't any made that fit totally correct. If you buy Convert/G5/SP gaskets, the pushrod holes will need to be altered and the resulting distance between the cylinder and pushrod tunnel is quite narrow and more prone to leaking/burning through.

"50,000 miles on it's originals". Have you used a borescope of removed a head for an inspection? If not, the chrome may be degrading and you just don't know it. I hear all the time about how the engine "runs fine and doesn't use any oil" and yet the chrome is flaking.

HMB is Germany sells 88 mm cylinder sets that already have the spigot machined down and the pistons assemblies matched to the 83 mm weight. The problem with buying from HMB is they don't package items for shipment very well and there's a good chance something will arrive damaged. 
Charlie
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abitloopy View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote abitloopy Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 16:29
Lots of food for though there, thanks!

For some time, I had a drum brake rear wheel, with cush drive, that I intended to fit to the GT. Then I thought that I'd never get around to restoring it, so I sold the wheel.......

950 cc cylinders that are machined to fit the GT crankcase and with correct weight pistons should certainly resolve any vibration problems, though.

Presumably, the 950 cc kits sold elsewhere (Gutsibits, for one) and advertised as not needing the crankcase mouths to be opened up should also have the pistons matched in weight with the 850 size. I'll have to phone them.

I've heard a few stories about badly-packaged Gilardoni kits. There was a damaged, new set for sale on Ebay earlier this year - presumably they got in that state for the same reason.

I don't want to be destroying the u/j or driveshaft (or mainshaft, I suppose,) so I'll have to think hard. I have learnt how to change gear sympathetically on Guzzis, though - I bought one new in 1978 and that was my daily transport for several years. That one was sold to buy a car (and then, I got a car with my job......I should stop selling things!)
Allan
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2019 at 16:54
Well, good luck with the project. Keep us informed of progress.....please.
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

1971 V7 Special. 1972 850GT.
1970 T120 Bonnie. 2009 500 Bullet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 09:11
When my LM2 had a piston to valve interface, I couldn't find any new pistons and so fitted a Gilardoni 950 kit.

I got the parts from HMB Guzzi in Germany and they turn down the bottom of the cylinders to fit into the 850 block. Everything lined up nicely and fitted fine using all original head parts etc. 


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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 09:43
That's interesting, did you find any difference in the level of vibration, or did it make no difference?
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

1971 V7 Special. 1972 850GT.
1970 T120 Bonnie. 2009 500 Bullet.
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abitloopy View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote abitloopy Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 10:20
Just what I was going to ask.....
Allan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 13:13
Originally posted by Amboman Amboman wrote:

"50,000 miles on it's originals". Have you used a borescope of removed a head for an inspection? If not, the chrome may be degrading and you just don't know it. I hear all the time about how the engine "runs fine and doesn't use any oil" and yet the chrome is flaking. 
I usually have a look from underneath when the sump is off for a clean out, which I do every other oil change. Perhaps I'll shine a a torch through the plug holes as it doesn't take long. My understanding is that adherence of the chrome plating is at least in part related to manufacturing quality - if they haven't flaked in 47 years.....
Nobody seems to fret about T3's - I think they have chrome bores too up to a certain year, albeit with an oil filter.
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Chris A View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris A Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 14:04
My T 3 had chrome bores...I believe they all did...went south at under 40,000 miles.
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 08 Nov 2019 at 14:25
My 850T had chrome bores,worn through to the alloy at the top at around 65,000 miles.
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

1971 V7 Special. 1972 850GT.
1970 T120 Bonnie. 2009 500 Bullet.
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