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pw50 Engine rebuild

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Hi guys, so I bought a tired old (87) pw50 which I am renovating over the winter for my son. I have resprayed the frame, and generally tidied up the bike changed plastics, tires, grips, cables etc. In general the bike was pretty tatty but being so simple they are a joy to work on. Now I am stripping the drive train and motor down. Originally I planned to just change the piston, on tearing it apart though I see the piston is in bad shape  and so the piston so I will change both of them as well. When you see how scratched the piston and cylinder is its amazing how well it ran:-) That said its clear the bike has done some time with an ineffective air filter so I will tear down the carb and I guess I should take a look inside the crank cases and replace bearings as needed. I have checked inside the transmission side and all looks clean and in good shape, but it looks like it at least needs a clean inside the crank case as it looks a bit mucky when I pear through the con rod exit. My first question is, based on peoples experience is it pretty straight forward to split the cases and replace the crank bearings? 2nd question is I have had one problem when removing the cylinder, one of the cylinder studs un wound out the crank case, and I noticed the threads were knackered (in the crank case). So I cleaned it up and removed the other 3 studs which were all good, and realised the threads dont go to the bottom of the holes for the stud. So in the damaged hole I tapped the threads deeper then the others. Whilst on this bad hole it probably doesn't have as much good thread as original (probably tapped the threads  3-4 mm deeper then the others) it does however seam to grip fine. Does anyone have any experience of dealing with damaged threads in the crank case? Or does anyone see any problem with tapping threads to the bottom of the stud hole? To me it seams to be working although I have not re installed the cylinder and cranked the studs to correct torque. I have just done a quick tapping job and wound the stud in hand tight and it seamed to grip fine, if any one has any comments this will be much appreciated. Cheers in advance for your help, Jim

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Crank bearings aren't difficult to replace. Splitting the cases without being rough is about the most difficult part. As far as the head studs, I can't remember the exact torque spec, but it was only around 10lbs for the pw head. Really it's a judgement call there, but if you do try, at least load up the threads with locktight.

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