Topend overhaul

[fayeslane]

The R100GSPD is approaching 100K kms, compression is down to 120 psi and it is using a little bit of oil. Oz winter is also approaching (think UK summer ).

I plan to do a top end overhaul at 100K and chuck in a timing chain. Rings, head job , push rod seals & carb overhaul.

It is running OK but noisier than my Bumblebee which has had a recent top end job.

What else should I replace? The aim is to set it up for another 100K kms and would like to do it properly rather than cheaply. Not looking for extra performance.

I'm wondering about:-
valves (look good thru plug hole)
cam followers
valve guides
push rods
big end bearings

Your thoughts............?

 

[Beemerboff]

If you order all the bits from Motobins up front it is only going to cost the same as one exhaust valve in Oz anyway.

Look carefully at the perimeter of the combustion chamber in the head - any signs of pre ignition and you want to open up the clearance between head and barrel to 90 thou at the perimeter and tapered out into the combustion chamber- not parallel as it probably is now.

Inlet valves and guides probably wont need replacing but they are cheap compared to the exhausts and the head guys like doing the lot.

My big end shells looked perfect at 200,000 km but you wont know until you have them apart - yours might be different.

You will need shims for the rockers , new big end bolts and a degree gage and special driver to tighten them - I am led to believe it is not torx but something special. A torx will get it apart -DAHIK.
You will also need someone who knows how to hone Nikasil barrels - a Porche dealer may be able to help, it is hard to find anything authoritative in the Airhead world. A light wipe with diamond impregnated Scotchbrite type material is how the factory did them.

Remember that all torque values are given clean and dry - if there is oil on the threads reduce values by about a third. The front top barrel studs are known to pull out easily.

Cam followers and push rods shouldn't need doing unless someone has really cooked the motor at some stage.
BMW recommend a 3 angle valve job- the dimensions are out there- try a google on "336 degree cam installation" - this has the head clearance dimensions too.
Have fun!