The Porsche option
SR owners can improve the performance of their engines, reduce mechanical noise, and claim a relationship with Porsche engineering for less than $100! Here’s how…
Valve clearances for the SR engine are set by simple screw adjusters with lock-nuts. While this system is simple and effective, it has some disadvantages. The contact patch on the adjusters is relatively small, and even with properly set clearances, the top of the valve stem is pounded without mercy in use.
The adjusters used in Porsche engines (p/n 90110537002) have a flexible cap at the end of the adjuster which fills up with oil and and keeps the adjuster in constant contact with the top of the valve stem. This means no tappet noise and minimal hard contact between the adjuster and the valve. Fitting the Porsche adjusters does require a bit of machining work, but no precision is required. You can do it with an angle grinder, a hacksaw and an old school ruler.
The Porsche adjuster is a bit longer than the stock adjuster, so you need to cut the top off it so it’s the same length. Use the same hacksaw to then cut a slot into the top of the adjuster so you can turn it with a screwdriver. You then need to grind about 4 mm off the end of the follower where the adjuster is located. The reason precision isn’t necessary here is that all fine adjustments are made by the adjuster itself when it’s in place.
It’s important to note, though, that unlike the stock item, you need to fit the adjuster to the follower before you put the followers back into the head. The stock items can be screwed in and out with the followers fitted, but the cap on the end of the Porsche adjuster prevents this. It’s no big deal as you had to remove the follower anyway to do the small bit of grinding. In case the amount of metal you take off the follower concerns you, the Club president’s bike ran this modification for many years without complications.
One last thing to consider is the follower itself. The followers fitted to the very late model SR400s from Japan have different oil passageways for lubrication and would seem to offer better protection and lubrication at the camshaft end. While the top end is apart, it might be worth considering a swap.