Tag Archives: Smart and Brown 1024 VSL

January 2015 – Progress report

Well, we are moving in the right direction (I think) but I’ve a lot of ambitions this year so we’ll see how it works out…

Last weekend I decided to drive up to Leicestershire to see Roger and to help him improve security at his place, following the break in the previous weekend that resulted in the theft of a Yamaha RD 350 LC YPVS F2 (the one I had when I was 18 years old.. 25 years ago). He’d bought lights and I bought an alarm system and over the weekend we fitted it all and made the best of a bad lot.
I love being in the workshop and he’s still pushing forward with improvements to machinery and tooling, the latest being a DRO on the beautifully made Smart and Brown 1024 VSL lathe. You don’t need them, but they do make life easier and quicker.
It’s also good to be surrounded by his Scott engine work and I think we help motivate each other to do the best we can to make sure that our racing Scotts are in good competitive order for riding this year.
Sometime on Sunday morning we had a visit from Eddie Shermer, the editor of ‘Yowl’ (journal of the Scott Owners Club) and a skilled engineer in his own right. He and his wife also put great energy into organising the annual ‘gathering’ of the Scott Owners Club held at Abbotsholme School in Staffordshire.

Eddie Shermer, Roger and Thiel 158 universal jig mill. They were smiling until the photo!
Eddie Shermer, Roger and Thiel 158 universal jig mill. They were smiling until the photo!
Eddie does a lot of Scott transmission work but also takes on complete engine rebuilds too, and came to discuss possible solutions to a particular problem he’d encountered with a crankcase. It was good to see him and always interesting to discuss the engine issues.
In fact, I kept a Scott line going through the weekend because I’d arranged with Alan Noakes in Lincolnshire that I’d take the Silk Scott frame up to him so that he could make a start on the frame connectors. Lincolnshire is hardly on the way back to Devon, in fact around 2 1/2 hours in the opposite direction, but it meant that I could see Alan and chat through some of the details and also see some of the things that he is working on. He had some hardened and ground clutch hub centres as well as pressure plates that he’d made on the bench, and also a very compact roller starter that he’d even cast the rollers for. Very impressive.
Anyway, I couldn’t stay long as I had a 6 1/2 hour drive back home! Just back by midnight.

This last week, I’ve removed the carburettors from the Super Squirrel as I need to make some modifications for the return to petrol. I never had the twin carb set-up developed for methanol anyway (switching back to petrol this year) so it’s not something that I wouldn’t have to do anyway. The two carbs are Amal 276, but are of different bore sizes at the moment. I need to get them bored out to 1 1/16″ and also have some short inlet ‘trumpets’ made. They won’t be very trumpet like, but will just have a better radius for the air flow.
I’ve also got some ‘K-type’ thermocouples which I want to fit to the exhaust, fairly close to the exhaust manifold, to give extra information when I take it to so a dyno setup when the inital carburettor modifications have been done. Petrol will make everything run hotter, and I’ll need to be careful to try to make sure that I do what I can to make sure that I’m not overheating the piston. I may also fit a temperature sensor to a spark plug to read that, as well as coolant temperature to see whether the small radiator is able to shed heat. It’s possible that I could pressurise the radiator to help the situation, but it might not be necessary. I also have a slightly rough, larger radiator that I bought many years ago from the late John Hartshorne, a prominent Scott enthusiast who had some wonderful stories, not least from his work with Wilf Green in bringing East German MZ’s into the UK in the years before the ‘Iron curtain’ came down.
Also on the agenda is crank counter-balancing. A Scott engine, being a 180° twin has reasonable primary balance, and normally they are known as being fairly smooth engines. They have almost no actual balancing on each crank assembly however, as the cranks are too small. The engine relies mainly on the large central flywheel to help dampen out the residual vibrations, which it does reasonably well. Some people have drilled the side on the flywheel on opposite sides to try to counteract the implied rocking couple effect but roger has never been convinced of the efficacy of this process. His own idea was to view each crank assembly in isolation and to work to try to balance at least as much of the big end weight as possible. In his ‘four bearing cranks’ he has two crank ‘discs’ each side, rather than the usual one. His enables him, using tungsten heavy metal (and Titanium rods) to balance the big end if nothing else. Rogers engine is very smooth, much more so than my own, and seems to want to rev more easily. We have ‘slugged’ single sided ‘Moss’ cranks in the past for a couple of people, and one of them cannot praise its smoothness enough. My cranks are not weighted, but I have some heavy metal slugs and I want to fit them. Normally, the holes are put into the cranks prior to heat treatment, as the final specification of the material conforms to around 50 to 53 HRC which is pretty tough stuff to machine. I’ve been looking into using surface coated solid carbide cutters rated up to 60 HRC to machine out for the slugs. I’ll post further information on the calculated % balance. I think it should be interesting!

Anyway, enough for now. things are happening! Even the Triumph head is back although a little more work needed here too.
I’ll try to not leave it so long as we go through the winter.

This weekends engine rebuild

After what must have been the longest Devon to Leicestershire trip I can remember doing, I arrived on Friday night with a view to getting the bottom end of the Scott Super Squirrel racer rebuilt by Sunday afternoon.

I knew that I was going to change the main bearings, as the ones I had were a bit notchy in the case. I also wanted to do some more gas flowing on the crankcase to allow me to use another inlet port that was blanked off by part of the crankcase as my calculations had shown that I was deficient in the inlet gas flow. I also wanted to check the static flywheel balance and the crank assembly end float and alignment.

The first thing I did was my porting as I knew I’d have to clean up the cases before replacing the main bearings.

Opening up the last inlet port.
Opening up the last inlet port.
It’s all so much easier with proper air tools! I’ve been spending hours with a riffler file to do stuff I could do with an air tool in less than half the time. Files are safer though! Easy to make a mistake with an air grinder.

Apart from a little de-burring here it is finished:

Just finished grinding the final inlet port access.
Just finished grinding the final inlet port access.
Scott cases ready and waiting for attention at Mossengineering
Scott cases ready and waiting for attention at Mossengineering
Roger working on a customers engine.
Roger working on a customers engine.

One of the first things we noticed when we looked carefully at the crankshaft assembly was there looked like there had been some movement on a crank taper. Wanting to err on the side of caution we set up a lap on his Thiel 158 jig borer to just make sure that the tapers were good and clean in the flywheel. A bit of gentle lapping and all was fine.

Lap for cleaning up minor surface damage in tapers.
Lap for cleaning up minor surface damage in tapers.

Next, we checked the static flywheel balance before ‘knocking up’ the crankshaft/flywheel assembly for checking the distance between inner control faces on cranks. This, we compare to the bearing face to bearing face measurement of the crankcase to determine the end float as you cannot feel and measure it by simply moving the crank side to side when installed as I used ball races and not rollers as standard.

Static flywheel balance
Static flywheel balance
Drilling flywheel for balancing
Drilling flywheel for balancing

See here Roger’s magnificent Thiel 162 horizontal jig mill. We dug out the floor with a mini digger and filled it with at least 1 meter deep of concrete to create a sturdy foundation for this. Table rotates 360° and flips up to 90°, whilst the whole machining column can move in and out. The spindle then can be moved forward/back and up/down.

Thiel 162 Jig mill
Thiel 162 Jig mill

Tooling
Tooling

The Smart and Brown 1024 VSL lathe is a good place to put up the crank and flywheel assembly between centres (he sells these if anyone’s interested) IMG_4182We measure skip and run-out just to make sure there are no problems.
Checking the crank assembly for run-out
Checking the crank assembly for run-out

I made a new key, using slip gauges to determine the width. You have to be careful to check the height of the key as well as the length in case these prevent the flywheel tapers from safely locating in the flywheel.

Flywheel/ crank timing key. This is to time only and is not for driving purposes.

After all this, and before the assembly, the old bearing were removed and the cases heated to accept the new ones. The 22 tooth drive sprocket was deemed to be too worn and a replacement was bored out to suit the spigot and fitted.

measuring for the new drive sprocket
measuring for the new drive sprocket

After that the new oil seals were fitted to the housing behind the main bearings and then the cranks finally installed and ‘knocked up’. The key doesn’t transmit load, it absolutely is not meant to… the taper has to do that. The crank tapers are driven in by tightening the centre bolt and then (with adequate provision to provide a dead stop on the other side) the centre of each crank is struck using an aluminium mallet, or large diameter drift alternately whilst continuing to tighten the centre bolt. There will come a point where the bolt cannot any longer be easily tightened and this is then considered done.

All in a very successful couple of days and a bottom end that should hopefully last for a while!