alan

As designed, the engine breathes through the cam bush into the outer casing. There is a hole behind the clutch cable entry point to get the pressure out, the oil drains back to the sump through the small hole in the inner case. Most people fit a blind bush on the cam to stop breathing into the case and plug the drain hole ( to stop water getting in when streams etc) . The engine then breathes through a hose fitted into he dizzy blanking plug, ideally with a non return valve to create a vaccum in the crank cases.

i have this one, uses the same 50mm dia filter as the morgo version. Cost me £45.00

Were there many at the pre 65 ? . I walked up to manmore on the saturday, there were quite a few electric mountains bikes.

No it is not mine, afraid i dont have pictures of the other side. I believe it is mostly original. It was bought new in october 68 by Hedley Cockshott, and was then traded in against a Bultaco. It now resides in Lancashire.

Unfortunately some so called experts (usually ones that manufacture parts) dont understand the basics of steering geometry. Making the forks looks steeper is assumed to be a good thing. If it is acheived by merely altering the offset of one of the yokes it increases trail. ( Unless you increase the offset of both yokes to compensate - in which case you end up with tiller like steering and the mass of the forks and front wheel acting on a long lever around the steering head bearings). If it is done by altering the rake angle of the frame it decreases trail. If you dont want to cut the frame the simplest options are to put longer shocks on the rear or drop the stanchions through the yokes.

All you have done by fitting parallel yokes is increase the trail, so it takes more effort to turn now.

420 and 428 are the same pitch so the sprockets will be the same diameter. i think you will struggle to find a 520 front sprocket. i have not come across a twin seal casing, is there enough room to space the sprocket out further without the chain rubbing on the back of the primary chain case ?

Yes, those are the dimensions of the offset sprocket . You will have to reduce the OD of the socket to go inside the recess.

Excellent service from trials bits ... http://www.trialsbits.co.uk/product_info.php?cPath=85_86_99&products_id=687

The standard clutch effectively has 4 plates.. The back of the drum acts as plate, adding another set of plates increases theoretical torque capability by 20 % for the same spring load. This should just about compensate for the increased torque due to the reduced engine sprocket. I havent used a four plate clutch so cant say for sure.

Hoover drive belt ?

You can get the 3 plate clutch to work but you need heavy springs and careful setting up. Without some sort of clutch lightener, you will end up with a heavy clutch lever.

no problem.. the issue is that when you compress rubber you don't change its volume just it's shape. The beauty of an o ring is that it just goes oval, the quad ring and tube have to spread out.. so yes i also use an O ring at the bottom, BS022 25.12 x 1.78 . There are a few choices.. you can trim the rubber tube and use just one, or remove the rubber tube and use up to 3. Do the dry build with the O ring on the top to determine the best way to go. Again you are looking to compress the O rings by around 20% of the cross section diameter .. good luck

i use a BS124 O ring which is 31.42mm ID x 2.62 dia. In a static application you are looking for between 15 to 20% compression of the diameter. That means on your dry build without any thing on top of the push rod tube you are ideally looking for a gap of between 2.0 to 2.2mm when you compress the bottom tube. You can trim the tube to achieve this if necessary. Any decent bearing supplier should have them. Simply bearings here in the UK are good for mail order. http://simplybearings.co.uk/shop/advanced_search_result.php?keywords=bs124 viton is the best material for this application, nitrile is OK, but avoid the epdm as it is not oil resistant.

The push rod tube seals are the same for all cub engines.. and a pretty poor design !!! The triumph design is the black tube at the bottom and a red quad ring at the top. The problem is that there is nothing to stop the top ring popping out if it is over compressed. The "solution" that one supplier has come up with is to use a gasket in place of the quad ring. The gasket should stay in place, but in order to seal it needs to be quite heavily loaded by the compression of the bottom tube when you pull the head down. There is obviously a lot less give in the gasket than the red ring so an element of trial and error is required to get the right set up. Different thickness gaskets are supplied to accomodate the different length barrels and different thickness head gaskets available. I would suggest you need to do a dry build to determine which thickness gasket to use, however I use a 70 shore viton O ring which is a lot less critcal on set up than the gasket, and a lot stronger than the red quad ring.

Go to 3.30 of the attached video. Gives a good demonstration of the advantages of gas pressurised shocks

the inside face of the chain as it goes over the engine sprocket is close to 2" from the centre line of the engine. so, if you have a 4" tyre on the centre line of the frame , the edge of the tyre is 2" from the centre line or pretty much in line with the inside face of the chain, leaving no space for a chain guard, a bit of clearance or any allowance for tyre defection. There are various options, all of which have some degree of compromise, pack out the engine.. but the exhaust and oil pump manifold will hit the frame before you get perfect alignment pack out the rear sprocket... the chain will miss the tyre but will be running out of line. You put more strain on the tapped holes in the hub and you may need to shave the outside diameter of the brake plate as it will rub on the overhanging sprocket if you go too far build more offset into the wheel.. but the wheels are then no longer perfectly in line. (bearing in mind that the frames were never that good that the wheels were perectly in line in the first place, and it would take a rider with the skills of valentino Rossi/Dougie Lampkin to have handling issues with a cub). The spokes on the RHS of the hub will be almost vertical, compromising the strength of the wheel. (hence the desire of wider hubs) so.. there is usually a compromise between any combination of all three which still usually leaves the chain and wheel running slightly out of line.

He borrowed a cub to ride with the Poachers in 2009

Considering that aluminium is 1/3 the density of iron, there is obviously a lot more material in the rickman conical hub compared to the cub cotton reel. i guess they did it to get better brakes. Comparing the similar geometry cub hubs, there is a weight saving for the aluminium version but not as much as you would first imagine as some of the sections especially around the brake drum are thickened up to compensate for the weaker material. Apart from the bling factor of the aluminium version, getting a 40 spoke rim, and finding an unworn, non -oval cast iron cub hub is getting tricky.

Going back to the original question, cast iron hubs are usually worn thin and oval. Alloy hubs are about 1/2 kg ligther I would start with seeing what rims are available. Original hubs are 40 spoke, Alloys are usually 36,(although i hear 32 spoke fronts may be available, it is not possible to drill the rear for 32 spokes). then there is the question of tube or tubeless rear . Personally i think the time will come when tube type tyres will be hard to get hold of. You can put a tube in a tubeless rim if the regs say you have to have a tube.. the only other consideration is the sprocket fixing pattern .. Not all hubs take the standard cub sprocket. Give whitton a ring, or try max heys, his number is on the armac website.

A simple extension of your logic that parts manufactured after 64 should not be used, or are you saying pvl ignition is ok, but you have to use a monoblock . in which case 100's or riders need to replace their carbs it has never been impossible to get a cub to run on a british made carb, being a democratic club, some 20 odd years a group of yorkshire classic cub riders managed to get a proposal passed that allowed cubs to use any carburettor. At that time the carb of choice was a second hand honda tl125 carb .Obviously cheap, and seemingly better wearing and requiring less frequent adjustment than an amal. No other 4 stroke was allowed this concession. As all the major event regs do not allow this concession most of the yorkshire cub riders had to have an amal or villiers carb to compete. interestingly the two top cub riders in the club run on amals all the time. To put all this in perspective , looking down the yorkshire results, there are less than 20 regular cub riders, at least 12 of these riders have ridden in scotland and have a suitable carb.. So less than 10 riders are affected. Only 9 members voted against the change at the agm. If riders choose to stick with foreign carbs they are more than welcome to ride in the specials class..

I assume your user name is a paradox, as you seem to be advocating the use of energy transfer ignition, monoblock carbs, and undamped forks.

Oddly the majority of yorkshire classic cub riders already own an amal so that they can ride in scotland ... Amal arent going to get rich of this rule change .. Maybe the rule change was suggested because an appropriate carb is available .... ??????

As i understand it the aim was not to bring the rules in line with scotland, that is just a consequence. The aim was to bring cubs in line with the club rules that apply to all other 4 stroke machine classes. yorkshire classic were the only pre 65 club to allow cubs to use foreign carbs, the regs for the northern british rounds, the manx the scottish etc do not make any exception for cubs. A years grace was given to allow anyone who has recently invested in a dellorto to at least get some use out of it . The point was made that cub riders in scotland do not seem to suffer from poor running issues .. And that includes dave thorpe on his 199