DRP: Derbi Reactivation Project

[toratora]

I started off making some decent progress installing the Bidalot RF70WR kit today, but I ran into two gotchas. The first one I was able to overcome with some hand tools, but the second one was beyond my local resources.


When fitting a kit there are some basics, like sussing out the squish, checking the ring gap, etc. To check the squish you have to clean things up, select a base gasket, fit the piston onto the rod with the little end bearing, slide on the cylinder, attach the head, and then take a measurement. Easy right? Well it is suppose to be easy.

A note with these photos. The last kit I installed on this engine was one of the Stage6 BR77s. The cases were slightly modified to match, and as can be seen here the Bidalot can accept an even wider transfer. Since the flow is up into the cylinder I was planing on leaving this as it is—which I still might do. There won't be any obstruction of the charge going into the cylinder, but there will be a slight reduction of through put.


The ring gap checked out okay at .2mm, but the wrist pin would not fit. It turned out to be that the piston was such that the bearing did not fit the piston. I was able to deal with this with some carful attention from a hand file, and some sand paper.


Next up was checking the squish, but that wasn’t going to happen tonight due to a complete lack of studliness.


Replacement cylinder studs are illustrated with the advertising for this kit. However, none came with this kit. I figured that on the Euro2 they must not be necessary. Turns out that’s not the case at all. The stock studs are way too short. You can get the head nuts started, but they cannot be torqued even enough to check the squish.


Another issue with the RF70WR is the placement of the head to cylinder attachment bolts. One is placed squarely in the center of the heads water outlet. I kid you not. Imagine losing the washer is this diminutive aluminum maze!


In happier news the paint matched up fairly well. Since it will be a while before I get some proper engine studs the paint should have plenty of time to cure.

[toratora]

I finally had a moment to remove the stock studs in order to get a measure on them. Had to employ the heat gun to loosen them up. Once out I measured them. They are longer than I expected coming in at about 120mm. The studs that came with the newer ProRace kit were 125mm. The silver one in the photo I got from Maxiscoot when I got the BRK kit. At 115.5mm proved to be too short for that project, and again with this one. I might be able to get away with 125mm studs for the RF70WR, but it might be better to get something a bit longer. Maybe even go with 130mm. I will have to check out what Treats has in stock.

[toratora]

I finally made it out to Treats to pick up the proper studs for the Bidalot kit, and tonight I had a moment to assemble the top end.


I had ordered a number of things from the Maxi via Treats, and was able to pick them up on Friday. I also picked up the studs for this project. When installing the studs I applied the permanent thread lock. It can be removed if heated up.


Installing the studs. I have to say the quality of these studs is top notch!


With these studs installed I could finally properly check the squish, which happily was right in the zone.


Once the squish checks out then the top end comes off again, gets slathered up with coper coat, and is then reassembled. I also applied some anti seize to the threads of the head bolts (not the stud nuts).


I then took a mini diversion to install the oil pump plate. I was sad to see that the bling came with a scratch. It is hard to see in most of the photos, but still bling should be bling!


The bling installed.


Since I’m employing the Stage6 reeds for the AM6 I had to apply a good slather of coper coat to ensure to air leakage action.


Things are coming together nicely.

[toratora]

A little more prep was accomplished today. After properly torquing the head it was time to connect the water pump feed. This was an issue because the Bidalot employs a much larger diameter, and creates a bit of a kink in the line.

This is combined with a much smaller spigot on the head which wont fit the standard hose. Additionally, there’s no place for a temp sensor! Lots of little issues to resolve.


And I finished going through the carb, so it is now ready. Here’s an exhaust port comparison with the Stage6 BR88.

[toratora]

It was exciting. The engine was going into the bike today! I got everything setup. Bike in place on the stand. Tools, and matts it place. Everything ready to go. The engine slipped right in. Wiggled it into place, pushed in the bolts, torqued them to spec, and started connecting all the other little bits. Then I saw this dark line that shouldn’t have been there—because I cleaned that area.












It was totally going great, and then it got all pear shaped. I saw a line of grease that shouldn’t have been there.


But it really wasn’t grease, it was another crack. And then I found another, and another. It is as if they were a disease spreading throughout the engine mounts.

[Berkeley]

WOW! thats suck big time.. just when you think it all good shit happens ahhhhh. whats the best way of getting the engine in? i take it you slide it in the side, rest it on the frame then raise a bit up at a time to fit it on the mounts?? was looking sooooo good!

[jkv357]

That does suck! Glad you caught it. Surprising how many mounts have cracked significantly.

I'll have to look my mounts over closely.

[toratora]

It will be quite a while before this bike will be ridable again. I agreed to move out of my place in San Francisco, and while I was in Santa Cruz the land lady dumped all my remaining stuff that was still at the house—which included the many body parts, carb, pipe, and who knows what else. It is devastating.

[Charounosaur]

It's a strange feeling when you search for help on the web, and your posts on how to do things are the closest you find.

I own the same bike as this one, but I didn't knew it had a balance shaft because mine was vibrating a lot. I just checked the workshop manual and indeed, there is one, it even explains step by step on how to set the balance, also the manual states that improperly balanced shaft will cause excess amount of vibration... My question is, would it stop vibrating as much if I set it correctly even though I'm running a 80cc kit with stock crank. Does your Derbi vibrate even though the balance shaft is set correctly?

[al_pritchard]

I have the same engine as well Charounosaur. Once I get it built with the 80cc kit I'll post up my experience with vibration.