Big Bore kit for the BMW DOHC engines

[NZHP2]

Originally Posted by shreddr

Hi Scott, you can run the stock rods as long as the wrist pin holes are in the same location relative to the piston deck (top). Wossner had made a high performance “kit” that utilized 3mm longer rods (128mm c-c) to slow down piston speed, and reduce forces towards the cylinder walls. If you have the pistons with the relocated wrist pins you will need the longer rods.


Sent from my iPhone using Tapatalk

Thanks Shreddr.

[shreddr]

I should also mention that you should get the 103mm head gaskets before you do anything, because they are hard to get, and mandatory to the modification. No head gaskets, no go!


Sent from my iPhone using Tapatalk

[NZHP2]

Originally Posted by shreddr

I should also mention that you should get the 103mm head gaskets before you do anything, because they are hard to get, and mandatory to the modification. No head gaskets, no go!


Sent from my iPhone using Tapatalk

Hi Shreddr,

Thank you for the heads-up, have you any suggestions on where I might look for a 103 gasket kit?

[shreddr]

Mine were a gift from Fralind, the patron saint of boxer motor modification I do recall they came in a Wosner package, so you may start with them. If you can’t get them from Wosner, Cometic makes custom gaskets, but they won’t be cheap.


Sent from my iPhone using Tapatalk

[NZHP2]

Originally Posted by shreddr

Mine were a gift from Fralind, the patron saint of boxer motor modification I do recall they came in a Wosner package, so you may start with them. If you can’t get them from Wosner, Cometic makes custom gaskets, but they won’t be cheap.


Sent from my iPhone using Tapatalk

Hi Shreddr,

The mechanic has come back with concerns over the width of the cylinder lining, particularly with boring it out to 102.96mm.

In your experience has there been any problems with the Wossner modification I am about to make making the lining too thin?

[shreddr]

I just realized you are talking about the R12S, I thought we were talking HP2S. Your mechanic is right, the R12S can’t be bored to 103mm. I forget what the diameter is, but if you do a search on the forum you can find it. In reality you can make huge improvements just by swapping pistons and rods for the Wossner hi compression kit, I think the combined weight savings was almost a pound of rotating mass, combined with a performance full exhaust (cat free header) and a good ECU tune will unlock lots of power without the need to do the bore job.


Sent from my iPhone using Tapatalk

[NZHP2]

Originally Posted by shreddr

I just realized you are talking about the R12S, I thought we were talking HP2S. Your mechanic is right, the R12S can’t be bored to 103mm. I forget what the diameter is, but if you do a search on the forum you can find it. In reality you can make huge improvements just by swapping pistons and rods for the Wossner hi compression kit, I think the combined weight savings was almost a pound of rotating mass, combined with a performance full exhaust (cat free header) and a good ECU tune will unlock lots of power without the need to do the bore job.


Sent from my iPhone using Tapatalk

Yikes, I was told it was doable - I'll see if I can cancel the order.

[NZHP2]

Originally Posted by shreddr

I just realized you are talking about the R12S, I thought we were talking HP2S. Your mechanic is right, the R12S can’t be bored to 103mm. I forget what the diameter is, but if you do a search on the forum you can find it. In reality you can make huge improvements just by swapping pistons and rods for the Wossner hi compression kit, I think the combined weight savings was almost a pound of rotating mass, combined with a performance full exhaust (cat free header) and a good ECU tune will unlock lots of power without the need to do the bore job.


Sent from my iPhone using Tapatalk

Hi Shreddr,

To your knowledge - Is there a high compression piston kit available that runs on the standard length Con Rods (125mm) as I don't think they make the 128mm rods anymore.

I have heard the HP2 rods which are 128 fit the high compression pistons??

Thanks for your help.

[shreddr]

Originally Posted by NZHP2

Hi Shreddr,

To your knowledge - Is there a high compression piston kit available that runs on the standard length Con Rods (125mm) as I don't think they make the 128mm rods anymore.

I have heard the HP2 rods which are 128 fit the high compression pistons??

Thanks for your help.

Hi Scott, I modified my R12S quite a while ago and at the time I got everything straight from Wosner. I don’t know where you are located (New Zealand?) but if I were trying to do the same thing again, I would tear down the R12S and send the stock pistons and rods to CP-Carillo and have them custom make a high performance set. IMHO you can’t do much better.


Sent from my iPhone using Tapatalk

[shreddr]

I just read through this thread again, the R12S is capable of being bored to 103, the HP2S can be bored to 105. Your pistons will work, I still recommend getting the gaskets first, and if you want to forgo the bore job, the CP-Carillo custom kit is still your best bet.


Sent from my iPhone using Tapatalk

[Droptarotter]

Hey Shreddr, good to see you are still alive and active here!
Hope you are well!

Cheers

[shreddr]

Originally Posted by Droptarotter

Hey Shreddr, good to see you are still alive and active here!
Hope you are well!

Cheers

Hi Bryan, how’s things?

I get notifications on my past PP posts, so I drop in every once in a while. I am only motoing on my GS so I spend most of my forum time in ADV but I definitely have a soft spot for the Pelican nest

I really dig the upright riding position of the adventure bikes, and I don’t feel the need to “speed” anymore, which is a good thing.

I have also jumped in with both feet on ebikes after getting both hip joints replaced, and have been raging on my homegrown dualie. Give it a try, it’s a game changer.




Sent from my iPhone using Tapatalk

[milnersXcoupe]

Originally Posted by pmc847

What is the difference between the R1200 and the HP2 cylinders? Are the studs in a different place or is it just the case bores (hp2) are larger to accommodate the 105mm cylinders? If so then I would assume that the R1200 cases could be bored to accomadate the 105mm cylinders. Your thoughts.

Philip

HP2 case stud locations R
spread further apart.

More case material between
bore hole / case stud

R1100 / R1150 cases
tend to crack when involved
in a crash.

Race Bikes Crash

Boring Out Stock Cylinders
is not a good idea

Factory designs in Heat Shedding
& Operating Temp Straightness.

Big Bored Factory Cylinders tend to run Hot

Big Bored Factory Cylinders tend not to run True


If you want a German Road Rocket
install a 3 Stage NOS system

Me-109s & FW-190s had great WOP
success with NOS

[kpolito99]

I purchased the Wossner 103 mm bore kit and have not experienced any overheating issues and it gets pretty damn hot in Tampa, FL.

I did however install the HP2S' larger oil cooler and oil pressure relief spring when I completed my engine upgrades.