Author Topic: Big bore 850 question  (Read 5451 times)

Offline guzzifan

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Big bore 850 question
« on: January 11, 2015, 03:09:09 PM »
Thinking of upgrading the 850 T to 1000cc via Gilardoni kits.  Has anyone done the conversion and what have been the results.  I'm  specifically interested in:

1). Increased vibration...how bad
2). Do you really feel any performance increase?
3). Any carb rejetting?
4). Would you do it again or go for 850cc's next time?

Thanks.
« Last Edit: January 12, 2015, 12:38:42 AM by guzzifan »

crc

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Re: Big bore 850 question
« Reply #1 on: January 11, 2015, 03:45:53 PM »
I did it to a 850t, didn't notice much more vibes, a little more power and it ran sweet with no carb adjustments, vhb30s

Offline Antietam Classic Cycle

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Re: Big bore 850 question
« Reply #2 on: January 11, 2015, 03:59:46 PM »
Thinking of upgrading the 850 T to 1000cc via Gilardoni kits.  Has anyone done the conversion and what have been the results.  I'm  specifically interested in:

1). Increased vibration...how bad
2). Do you really feel any performance increase?
3). Any carb rejetting
4). Would you do it gain or go for 850cc's next time?

Thanks.

1) more vibration, not terrible, sort of like the carbs weren't synced.
2) noticeable amount more low-end torque, but not much more hp without breathing modifications.
3) not on the Eldos I've done.
4) I do whatever the customer pays me to do.  ;)
Charlie
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Online Perazzimx14

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Re: Big bore 850 question
« Reply #3 on: January 11, 2015, 05:52:24 PM »
I've had the choice to add the BB kit on my Eldo, 850T and T3 and went stock. To me unless you are going to commit to spending the money on head work, better carbs, balancing of rotating bits and a more aggressive cam why bother.

Money better spend would be adding a second disc & caliper, lightening of the flywheel, FAC dampers and a set of nice rear shocks.
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Re: Big bore 850 question
« Reply #3 on: January 11, 2015, 05:52:24 PM »

Offline jabberwocky

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Re: Big bore 850 question
« Reply #4 on: January 12, 2015, 05:39:40 AM »
I'll play the other side then. My T3 has a big bore set up (89mm Venolias in iron sleeves). I have never ridden a stock 850 motor, so I can't speak of the relative smoothness or power of the two. I kind of feel like why wouldn't you go to the big bore, IF you're doing the top end anyway. If your current stock 83mm top end is in good order, then it's probably not worth the cost. It doesn't cost much more than keeping the stock bore, and it is a bolt on setup. By all accounts I've heard, you DO get more low end grunt, even if you don't gain at the top end without doing other upgrades. But later on down the road, you can still do these other upgrades and realize more gains, because you've done the groundwork.  My bike, which I built up from someone's parts collection that I bought, is not the smoothest thing going at low revs, but it is not at all objectionable with the stock carbs balanced well. Above 4K though, it is soooooo nice and velvety smooth! Below 4K, my R100 is smoother, above the Guzzi is smoother.I'll also add that while I did take great care to get the two Venolia pistons balanced to within 1 gram, I did not do any balancing work to the crank, so perhaps with some more work, things would smooth out more. I'm totally happy with it, so I'm going to leave  it alone until it needs to come apart for some other reason.

Offline nick949

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Re: Big bore 850 question
« Reply #5 on: January 12, 2015, 06:32:31 AM »
I'll echo what others have said. 

My 1972 949 Eldorado is a bit rough below 3500, but with lots of torque at low revs. 
The 1974 850 California I had was a lot smoother throughout the rev range.  Only slightly less torque (still more than enough) but definitely smoother.
I won't go back to 850 now, but if I had to replace the cylinders for some reason, I'd go for stock.

Nick

Offline steven c

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Re: Big bore 850 question
« Reply #6 on: January 12, 2015, 08:00:11 AM »
 I rode a big bore T for 13 years 973cc from a company out of NYC ,something Machine, early 80's. Nice increase in torque, and never really noticed the increased vibration.
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Offline PeteS

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Re: Big bore 850 question
« Reply #7 on: January 12, 2015, 08:07:47 AM »
A friend had a 1000cc LMIII that made close to 80HP. Along with the big bore it had head work by Manfred Hecht, 40 mm carbs, B10 cam, etc. I rode it and its was every bit as smooth as stock and still got over 50MPG.
How fast do you want to go? How much $$$ is it worth?

Pete

Offline Antietam Classic Cycle

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Re: Big bore 850 question
« Reply #8 on: January 12, 2015, 08:51:33 AM »
I rode a big bore T for 13 years 973cc from a company out of NYC ,something Machine, early 80's. Nice increase in torque, and never really noticed the increased vibration.

Notice the OP said "via Gilardoni kits". Sure, other big-bore set-ups might be smooth, but unless measures are taken to lighten the piston assemblies, the 88 mm Gilardonis won't be.
« Last Edit: January 12, 2015, 09:50:22 AM by Antietam Classic Cycle »
Charlie
http://www.AntietamClassicCycle.com
'69 V700
'69 Ambassador
'71 Ambassador
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Offline bobdar

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Re: Big bore 850 question
« Reply #9 on: January 12, 2015, 08:56:02 AM »
Anyone know the assembled piston /wrist pin / rings weight difference?  Can that difference be milled out of the big bore piston?
bob darcey
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Offline PeteS

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Re: Big bore 850 question
« Reply #10 on: January 12, 2015, 09:17:14 AM »
Anyone know the assembled piston /wrist pin / rings weight difference?  Can that difference be milled out of the big bore piston?

I don't recall the numbers but the 992 kit pistons are lighter than stock. They are a slipper design.

Pete

Offline Gliderjohn

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Re: Big bore 850 question
« Reply #11 on: January 12, 2015, 09:49:41 AM »
My T-3 has more vibration. If I had to do it over again I would probably spend the money for balancing. The additional vibration is actually quite small but it is just right to make my nose want to itch like mad at times. I cannot really comment on the power differences since I changed cams, went to 36mm carbs with a port and polish,etc. It does run very nice and strong. At highway speeds I rarely have to shift down to make a quick pass and that includes when double up.
GliderJohn
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