R80 G/S heads with big bore from Siebenrock

bernardofeio

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hello

does any one know if I can use R80 G/S heads (1987) with big bore from Siebenrock?

I have some heads in an old bike that eventually I will try to use on the already existing kit. The engine was working ok with R100 heads.

I don't want to take the heads out before knowing if they will work. It has 32 Bings

thks
 
I believe the definitive answer is on Seibenrocks website??

If you mean the 1000cc kit (?) then yes - its a plug and play kit, and what I have on my R80 G/S - and all the better for 32mm carbs.
 
You can, but it'll feel even more short geared than it does now. Siebenrock's high fifth gear is a good addition.
 
Seibenrock do two 1000 cc kits,
The 800 to 1000 has a machined piston crown so it will work with the smaller combustion chamber on the g/s cylinder head.
They also do a 1000cc power upgrade which does not have the machined crowns and is for use with 1000 cc heads.
If you already have the 1000cc kit it can still be used ,but the 80 heads will need a small amount of machining to allow for squish.
Pretty much any engineering shop with a lathe will be able to do this for you.
 
Here is a pic of the 800 to 1000,
You can see the machined step at the piston edge,this is to ensure clearance as it moves into the smaller 80 combustion chamber
 

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Seibenrock do two 1000 cc kits,
The 800 to 1000 has a machined piston crown so it will work with the smaller combustion chamber on the g/s cylinder head.
They also do a 1000cc power upgrade which does not have the machined crowns and is for use with 1000 cc heads.
If you already have the 1000cc kit it can still be used ,but the 80 heads will need a small amount of machining to allow for squish.
Pretty much any engineering shop with a lathe will be able to do this for you.

Does the kit come with machining details?o
 
We have fitted a fair few,800 to 1000 conversions,
It won’t make it any faster but it gives a fair bit more midrange torque,at the end of the day it’s still breathing through small(er)valves and 32mm carbs ,so they tend to get a bit breathless up the top end when compared to a 1000 with bigger valves and carbs.
I like the 800/1000 conversion:thumby:
 
We have fitted a fair few,800 to 1000 conversions,
It won’t make it any faster but it gives a fair bit more midrange torque,at the end of the day it’s still breathing through small(er)valves and 32mm carbs ,so they tend to get a bit breathless up the top end when compared to a 1000 with bigger valves and carbs.
I like the 800/1000 conversion:thumby:

Thanks Mikey that’s useful information
 
Seibenrock do two 1000 cc kits,
The 800 to 1000 has a machined piston crown so it will work with the smaller combustion chamber on the g/s cylinder head.
They also do a 1000cc power upgrade which does not have the machined crowns and is for use with 1000 cc heads.
If you already have the 1000cc kit it can still be used ,but the 80 heads will need a small amount of machining to allow for squish.
Pretty much any engineering shop with a lathe will be able to do this for you.

Is the crown thickness standard size on all pistons mike?

Not sure what you mean?

I was just wondering how much you could take off the crown safely.
 
I think Mikey says that you take it off the head, either with a lathe, or perhaps some careful hand work if you are feeling clever.
I like to aim for around 60 thou squish clearance for safety - the old 16g -1/16" copper head gasket let you set piston deck hieght at zero and know you were close, and it worked OK.

IMHO on today's speed restricted roads most airheads are over geared and benefit more from a reduction in gearing rather than increasing it - a 1000 cc R80 G/S on 37/11 gearing will pull strongly from 60 km/hr with a pleasing instant throttle response, in top.
If you increase top gear the most noticeable difference is that it knocks the edge off the throttle response, without noticeably reducing engine revs - you won't notice 200 revs on a well tuned bike - worst bang for the buck you can spend on an airhead.
FWIW I have just changed the final drive on my 900 cc R75/7 from 32/10 to 37/11 and performance wise it is probably the best performance bang for the buck you will get, instant throttle response , less gear changing, better fuel consumption and cruising at the state limit of 110 km/hr I just dont notice and difference in revs.
And cheap too, as no one wants lower geared final drives I only paid $110/50 quid for it!
 
I think Mikey says that you take it off the head, either with a lathe, or perhaps some careful hand work if you are feeling clever.
I like to aim for around 60 thou squish clearance for safety - the old 16g -1/16" copper head gasket let you set piston deck hieght at zero and know you were close, and it worked OK.

IMHO on today's speed restricted roads most airheads are over geared and benefit more from a reduction in gearing rather than increasing it - a 1000 cc R80 G/S on 37/11 gearing will pull strongly from 60 km/hr with a pleasing instant throttle response, in top.
If you increase top gear the most noticeable difference is that it knocks the edge off the throttle response, without noticeably reducing engine revs - you won't notice 200 revs on a well tuned bike - worst bang for the buck you can spend on an airhead.
FWIW I have just changed the final drive on my 900 cc R75/7 from 32/10 to 37/11 and performance wise it is probably the best performance bang for the buck you will get, instant throttle response , less gear changing, better fuel consumption and cruising at the state limit of 110 km/hr I just dont notice and difference in revs.
And cheap too, as no one wants lower geared final drives I only paid $110/50 quid for it!

A large dose of agreement with this - having had a higher 5th fitted to a box on a previous bike, I was really rather underwhelmed by it, especially given the cost and hassle of fitting it. A proper 6th gear is what it really needs!
 
The 800 to 1000 kit is already machined and ready to fit:thumb
If you are happy to remove and refit the heads and barrels jobs a goodn:D
It’s well worthwhile having the bike run on a dyno though as they can run a bit rich after the conversion,so a bit of a rejet might well be needed.
Last one we did needed a size smaller on the main and idle jets and the slide needles dropping one notch.
Machining of the heads is only required if a kit for an existing 1000cc engine is being fitted in conjunction with 80 heads
 
The old way of doing things was to bolt on the head with something on top of the pistons, Plasticine or 120 thou plastigauge, and find out what clearance you have between the head and the piston, and the shape at the perimeter of the combustion chamber.

Once you know that you can decide the best way to proceed. Then you decide what is possible, hand work is slow, so a pro will use a machine tool to cut either the head, which is the safer option, or the piston, which has more potential to cause problems.

Some folks suggest that you want the clearance around 60 thou, either parallel or increasing towards the center of the bore.
You might find that there is sufficient clearance at the perimeter of the new bore and the problem area is where the dome on the new piston meets the edge of the smaller chamber in the head, and you could probably grind that off by hand, but extending / deepening the chamber in the head to match the new bore is probably a job for a machine shop.
You might even find you have too much clearance, in which case you might want to take a little off either the bottom flange of the barell, or by refacing either the head or the top on the barell.
Some suggest shortening the push rods buy the same amount , but for the little you will be taking off it is probably not needed.
The 1000/1000 cc Siebenrock in not needed if your barells are OK, as Motern Israel sell the Wossner pistons separately, and head work is probably not needed if you buy the correct kit, as Mikey has said, it is just reassuring to check that everything is OK so that you get the maximum benefit from what can be an expensive exercise, and your bike may have been modified at some time in the past.
 
A large dose of agreement with this - having had a higher 5th fitted to a box on a previous bike, I was really rather underwhelmed by it, especially given the cost and hassle of fitting it. A proper 6th gear is what it really needs!

True, but that would be significantly more hassle :D

My G/S feels horribly undergeared in modern traffic, revving it's tits off at 70/80mph cruising speeds. I'm not going to change the gearing though as it's generally a pretty standard bike otherwise and it would be a shame to alter it too much.

I did fit a big bore Siebenrock to a friends G/S though, and that felt even more under geared. At a later date, I fitted a Siebenrock high 5th gear that improved the situation a lot, both in mine and the owners opinion. It was also a lot easier to fit than the low 1st he also wanted.
 
My G/S is still the standard 800cc however, Mikeyboy put the higher 5th in it. As Mr Boff says, it's not majorly noticeable, but it does make a bit of difference on longer journeys.
 


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