Help with identifying

[byron]

Just over 12 months ago I bought an 86 g/s Paris Dakar. I used the bike throughout the summer putting almost 3000 miles on it. The previous owner had only done 100 miles in the past 9 years. Towards the end of the year the bike developed oil leaks from 2 pushrod tube rubbers and the neutral switch, so it is up on the ramp for some tlc. Oh it is a 33k miles from new bike.
First side is stripped and I am checking my gasket set and the head gasket does not match. A bit of investigation tells me that the bore is almost 94 mm.
So my question is do I have a 1000cc upgrade. I am assuming I cannot use the 800cc cylinder head gasket? and should I buy just a 1000 cc head gasket , as I think all the other gaskets and seals match. Also my bike has an external oil cooler mounted on top of the right crash bar, which I have just read is a suitable upgrade for the increase in capacity . I also cannot see any BMW mark's on the barrel, but there are some other
mark's. Seibenrock perhaps ? I struggle with photos on here but will try soon to add some.
PS - the bike spent the first 25 of its life in Austria.

 

[byron]

Just over 12 months ago I bought an 86 g/s Paris Dakar. I used the bike throughout the summer putting almost 3000 miles on it. The previous owner had only done 100 miles in the past 9 years. Towards the end of the year the bike developed oil leaks from 2 pushrod tube rubbers and the neutral switch, so it is up on the ramp for some tlc. Oh it is a 33k miles from new bike.
First side is stripped and I am checking my gasket set and the head gasket does not match. A bit of investigation tells me that the bore is almost 94 mm.
So my question is do I have a 1000cc upgrade. I am assuming I cannot use the 800cc cylinder head gasket? and should I buy just a 1000 cc head gasket , as I think all the other gaskets and seals match. Also my bike has an external oil cooler mounted on top of the right crash bar. I also cannot see any BMW mark's on the barrel, but there are some other
mark's. Seibenrock perhaps ? I struggle with photos on here but will try soon to add some.
PS - the bike spent the first 25 years of its life in Austria.

Top of the barrel with approx size

 

[byron]

A few more pics to help

 

[byron]

Here is the old and new gaskets showing the variation.

 

[DrFarkoff]

That is a standard R100 Piston

94mm is standard bore

All 1000cc models 94.0mm (3.70")
http://www-cdr.stanford.edu/~petrie/bmw/R80ST/engines.html

 

[gog]

R80 barrel bored out to accept r100 pistons? The 80 with an A (800) scored out and restamped C (1000)

wonder if the heads were machined to allow use of the 100 pistons, or replaced with r100 heads

 

[Gelandestrasse]

Replace like with like gaskets - not the R80 ones. This was and still is a popular mod. I had an ST with 1000cc pots and I think they may have been Siebenrock but difficult to tell. If yours are standard R100 pistons then that tends to rule out a Siebenrock power kit. It's likely you have Nicasil bores so a re-bore unlikely. Ride and enjoy!

I looked the carburettor numbers and jet sizes on mine to double-check they were suitable for 1000cc. They were original ST R80 carbs but had different main jets. Haynes manual is good for reference here.

You may wish to let your insurance company know.

 

[byron]

Thanks for the comments, all clear now