CB Engine Woes

If you and your mechanic take it apart and after measuring the case all that's wrong is the thrust is pounded out, someone with a line boring bar (for cutting the case for oversized bearings) can re-cut the thrust surface. Bearings are available in all sizes (standard to I think 3rd oversize od) for wider thrust cuts. While a VW engine needing a thrust cut at rebuild time is not unusual, the thrust being pounded out after just 6,000 miles is.

Hope this helps. Al

What weight pressure plate is in it? Do you pop it into neutral and take your foot off the clutch pedal at stop lights and periods of idling or leave it in gear andjust keep your foot on the pedal?

Thanks Al, Not to sure about the weight of the pressure plate, seem pretty much standard. I usually leave the clutch in at stop sign or signals UNLESS it is a long light in which case I take it out of gear. I can't speak for those 3 previous owners habits though so who knows? I'll check the thrust surfaces though! Thanks!

With 1/4" of movement and the bearing moving as well, the thrust surface in the case will definitely need to be cut. With the expense of stocking so many different bearing sets, some shops only stock the maximum thrust size, machine the thrust surface in the case back to good, and then measure and cut the inside of the surface on the bearing to fit.

And even completely stock engines can get pounded out like that. I've seen cases pounded out so far that the biggest oversize thrust bearing won't fix it. In the late '70's/ early '80's I used to hang out at a friend's VW performance shop a lot (much younger and not yet married, I drank way too much beer there after hours! What can I say- I'm a product of a mis-spent youth), and Don would fix cases with the thrust too far gone with a Triumph piston ring (sorry, never knew and didn't care at the time exactly what it was from) as a spacer. Al

So is it better to put the car in neutral and let out the clutch or sit at the light with my foot on the clutch with the car in gear?

I think the idea is that when your pressing the clutch your straining the system and creating pressure that causes wear. Obviously we all tend to just put in the clutch at a stop sign or quick light but IF your there for a longer time it's better to take the tranny out of gear and let it be in the normal non stressed position!

Pedal in or pedal out at the light is an old, old question, and in VW/Porsche land, the story goes back to the early days when the thrust (throw-out) bearing in the clutch was no bearing at all, but just a ring of graphite.  It was meant for only intermittent (shifting) use.  If you just kept the pedal down, it would wear out a lot faster.  So I always put the car in neutral at a light, even though nowadays I really don't have to.  Old habits, and all of that. Those brilliant but cost obsessed VW German engineers are responsible for this.  Eventually, saner minds prevailed, and actual bearings with balls (or rollers??) were applied to this problem. How excessive clutch depression contributes to the problem described above is way beyond my ken.  Listen to ALB.  Seems as if despite his alcohol fogged misspent youth, he managed to pick up a  thing or two.

If you have a heavier than stock pressure plate, Robert, it's a very good idea to pop it into neutral every chance you get. While most aircooled stuff VW built is somewhat over-engineered and will stand up to the abuses of more power, the thrust surface is barely adequate for a stocker.  Magnesium is not that strong a material, and the case getting pounded out, as I said earlier, is not unusual at all. It's also common practice to line bore the case at rebuild time, again, because even high mileage stock engines will overstress the case. This is why main bearing come in standard and 3 oversize outside diameters (as well as standard and 3 oversize inside diameters for re-ground crankshafts), and I think 3 thrust cut sizes as well.

Drag racers using twice the plate pressure sometimes move the thrust surface to the middle main bearing, where there is room to bolt in a steel plate to absorb the forces of such violent launches. It's a fairly involved procedure, as the crankshaft has to be machined specifically for it as well. 

Kelly- Yeah, I still remember the odd tidbit, so it wasn't a total waste of time!

The thrust getting pounded in the case at 6K miles is a sign of a problem somewhere. Like I had mentioned in our email, make sure the input shaft has not bottomed out in the gland nut. Also, if the clutch was adjusted too tight, it can cause premature wear on the thrust bearing and engine case. Your engine has a stage-1 kennedy clutch, not heavy enough to pound the thrust bearing into the case at 6K miles.

The engine does not need to be replaced nor does the engine case. The case can be bored +.020  and thrust cut . We machine a bearing to fit the newly cut thrust surface of the case, pretty much standard procedure for the last 40 years.

   But, the underlying issue to the problem needs to be found or you will be right back in the same position you are in now.

Thanks Pat we'll do that! Since 3 other owners had the engine prior to me it's pretty hard to determine what happened? 

Which brings up a funny reality. My Buddy Larry Markham is a Porsche specialist and highly skilled engine builder of over 40 years. We've been friends since 1976. He is an old Drag racer and somehow got into 356 Porsches. Like almost ALL other Porsche mechanics he WON'T touch a VW! Same for VW mechanics I've delt with. There seems to be a MUTUAL dislike of the others product even though they came from the SAME Man, the SAME place, and created on the SAME Principals! So when I started coming over to Larry's in my Replica Speedster instead of my 1958 366A Super Coupe Larry was well..not thrilled. Then one day he's looking at my engine and says' Humm you sure have a LOT of movement on that lower pulley!" We did the static test and the crank was moving a LOT! Gulp. Even though he DOESN'T work on VW's and had "NEVER even taken one (a VW engine) out" he agreed to let me pull my engine in his Home garage. I suppose his old Drag Racer self kicked in as we pulled the CB engine out he began to be impressed by the quality of the engine and the high end parts that were coming off. When we finally got the flyweel off (had to get a special 1 1/2" socket since it's not the usual 36 mm) and put a dial on the flywheel it became aperant that things were worse than we thought! The rear main bering was sliding back and forth on the crank. I looked glumly at the unfolding scene in despair. I was looking at an no win situation. I didn't figure Larry would want to rebuild my engine and wasn't sure anything but the externals were worth saving. Despite having a medical proceedure the next day Larry called me and said "Rog you know this ain't Rocket Science, WE CAN rebuild this engine!" I was amazed as he NEVER does ANYTHING related to VW's!Funny I've owned VW's & Porsches and never thought twice about one being anything but the others Brother!

Rocket science?? Did someone say Rocket science??

I guess it's comparable to a Mercedes' mechanic working on a Chevy Cavalier.