Tuesday 26 March 2024

QR50 - a bit of a service

 After three years in the field, the little beast is back. The boys are complaining the bike has no power after ten minutes running and with busy lives, my son and daughter in law have no time to check it out - so it’s back to Grandad’s workshop.

The Square Four is now off the bench to test the kickstart against the clutch, and then close up the clutch, refit the exhaust and test ride it. All went well with that, so the QR can go on the bench:


The first thing to attend to, and rather alarming, is the fact that the fork top threaded inserts are both loose. Now, these had a ring machined into them which allowed them to sit in the top of the fork leg, which I welded into the fork leg. Now, there is no evidence that the ring was anything other than an interference fit around the insert - indeed, there is no evidence that the insert was anything other than an interference fit in the fork leg.

Now, the inserts are retained in the fork leg by two strong plugs welds on each side of the leg:


The lack of power appears to be down to the choke - the choke cable goes into the carburetter through a plastic nut which has broken, allowing the choke cable to come out. When it comes out, it appears to operate the choke such that the mixture is rich all the time, even with the choke knob pushed in. That will certainly lead to a lack of power.


Friday 22 March 2024

Gearbox Done

 After spending the winter rebuilding the gearbox and the clutch, I'm pleased to be finishing the job as the weather warms up.

First job, before finally closing up the gearbox is to fit the kickstart stop rubber that has been waiting on the bench for literally years. I needed to remove the metal part of the stop and reduce the 1/2" OD to about 7/16" to get the rubber to go over it. I mangled one in the process of realising that, which delayed the job by a week:


Next, when the kickstart is on and the gearchange mechanism is timed, I need to fill the gearbox. This is easier said than done as on a SQ4, the filler is hidden behind the oil pipes. Surgeon's forceps are useful to get it out:


Since the Morris K400EP grease is quite fluid, the easiest way to get the grease in is to use a syringe. This is a 250 ml syringe and you need 750 ml. It's got a flexible hose and a rigid copper pipe on the end to get the grease through the filler and into the top of the gearbox. You can fill the syringe by sucking the grease out of the tin:


Next time i do this, I'll do it warmer weather. This was hard work:


In a departure from usual practice, I've measured the oil going into the primary case - 150 ml of engine oil, to determine how much I can get in without it leaking.

I'll road test it, then see if 150 ml is too much or not enough.

Running the engine on the rear stand shows I can select all gears completely silently. It's never been as good as this:



Wednesday 6 March 2024

FH Barrel

 While waiting for the kickstart rubber, I've degreased the FH barrel in the cleaning tank and given it  good scrub and scrape. Removing the rings from the new + 0.060" IMD pistons and testing them for fit reveals a nice 0.004" clearance in both barrels, per the IMD recommendation.

Therefore, it's time for a coat of engine paint. This is the same stuff I used on the W/NG which seems to have survived OK:



Sunday 3 March 2024

New Clutch Plates

Are events coming back to bite us? In this recent post I commented on some intermittent clutch problems - maybe we are now finding the cause.

Three of the four plates are like this, and the colour reveals they have been hot:


This is a new set from AOMCC Gearbox spares, laser cut, a realistic price and flat as a pancake.


We are getting near closing up now. All I need is a kickstart rebound stop, which is coming from Draganfly, and I can refit the kickstart and the gearbox end cover. Then I can test the kickstart and set up the clutch.

Sunday 25 February 2024

Burman Clutch Centre

 Over the last few days I've assembled the primary drive and the clutch, tightening the mainshaft nut in the process.

I've installed the clutch spring studs with Loctite 271, the red thread locker. That won't come loose; originals were peened in place, but it's not 1950.



Fitting the plates revealed some rocking. I pulled them all out again, and found that three of the four plain plates were distorted by up to 2 mm, and discoloured from heat.

Geoff will send some new ones tomorrow.