Thursday, February 27, 2014

Which shims go where inside a Derbi Piston Port Engine.

So as I keep rebuilding engines, I have noticed that I have been relying less on manuals and more on just what I see. So I'm doing a rebuild on a Derbi piston port engine for my TAT Derbi. I picked up a trashy yellow 1979 Derbi T.T. (stands for Tough Terrain :D) off Charley from BLK BLK. It's pretty crusty but its actually in better condition than I expected. Plus a little trashy is rad so I wont feel bad if I weld all over it. 

 So we all know what it is like to take an engine apart, leave it sitting for a month and then forgetting where everything goes.... Then looking at the manual and pictures that contradict what you are seeing. I find that engine repair manuals can be confusing and I'm personally a hands on learner.  There is nothing better than an unmolested complete bike to take apart and put back together. So I documented where all the shims go in this engine because I've noticed some discrepancies in the manual. Also this was a FUNNY wrenching session because I recently moved and don't have a work bench yet. Man it brought back early rebuild memories of oblong greasy engines rolling around every time I touched them.Keep in mind this is just to show the shims and Im going to clean everything up a TON. FYI The manual I am using is from 1979 which is the same year of the bike that I am taking apart. 

First lets take a look at a few images from the manual. These look like they were taken with a Logitech Beta webcam and are -2 megapixels, they really dont help at all. 

Oh yea! Let me zoom in there and see that at 300% a shim looks like a lego. 

So I'm here for the boat anchor party.
Not bad inside...
Needle bearing and washer/spacer for the rear varo shaft.
Hard to see but the washer/spacer is tapered and the smaller side goes down into the shaft.
Both in place.
Little rusty.
These 2 washers come off right side of the main gear on the pedal shaft.  One is a bit (~1mm) larger around and 1mm smaller in thickness than the other. The larger one measured 33mm OD x 16.2mm ID x  2mm thick and the other one measured 32.3mm OD x 16.2mm ID x 3mm thick. This is where I noticed one of the discrepancies in the manual.  

As you can see, the two shims I listed above are shown as one shim (#37) and is listed (below) as 32.3mm OD x 16.2mm ID which is the right measurement. Another few weird things with this diagram is that the needle bearings and spacer listed as #34 and #35 are in my engine just one big needle bearing. Lastly if you look a few pictures down from here, there is a photo of the shim on the left of the main gear that rides on the pedal shaft. Its in the above diagram listed as #33 I measured it and it is the exact same as #37 shim (32.3mm OD x 16.2mm ID x 3mm thick) but in the list below, it is listed as 19.2mm x 32.3mm. That doesn't make sense because if it rides on the same shaft as the other bearings it should be listed as a 16.2mm ID and not 19.2mm ID. 

Actually a few pages later in the manual it lists some of the shims from above that measured 25mm OD x 16.2mm ID x 3mm thick as being 26.1mm OD x 19.2mm ID x 1mm. Doest make sense how the manual keeps listing the ID of washers that ride on the 16mm pedal shaft as 19.2mm. 

This is the #33 misprinted "19.2mm ID" shim which is really 16.2mm ID.

These 2 shims are 25mm OD x 16.2mm ID x 1mm thick. Listed in the manual (#26) as 26.1mm OD x 16.2mm ID but hey it's close enough. 
If you have ever rebuilt a Derbi PP engine you know that removing the "shifting dog" is the fun part. LOOK OUT FOR FLYING BBs!
Tap tap tap.

This furthest left shim on the pedal shaft measured 22mm OD x 16.2 ID x 1mm. Below it is listed as #8 the "righthand pedal washer" but once again wrong spec listed as 19.2mm ID. 

One last thing I thought was strange is the poor quality of the main gear in this engine. I mean look at that... Cmon Derbi!!! Everything else looks great though and the crank will probably work just fine one it's cleaned up.

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