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By tweaks do you mean purely adjustments or replacing the rear suspension unit with something else and changing the front forks damping characteristics? If it’s just adjustments then can I suggest that you make single adjustments to one end then the other after you have tried the bike after each ‘tweak’. On this website you will find many references to suspension set up and the best adjustments tend to be the ones coming from the people that designed the bike in the first place....the manufacturer. If you are set on going it alone then first weigh your self in your normal riding kit. Should you happen to be on the er ( politically correct description...fat b’stard) larger size then that opens up an entirely different approach. We are all different and cope with life in our own ways, but the suspension of a competition machine has been chosen to suit the Mr. Average size....bear this in mind if your bikes bottoming out with little action needed. Static sag, set this first, then get on the bike with normal riding gear and note changes front and rear, you may need a helper here to take measurements...unless of course you have really (politically correct description...arms like an orangutan) long arms. You are looking to pre load the suspension so that your combined weight together with the static settings allows full suspension movement without bottoming out...reaching full compression and banging into the end of travel. If you’ve been riding for a whole year without taking advantage of adjusting the suspension then you have been missing out on transforming both the machine and your abilities. Hope you have some good results from ‘playing’ with the suspension, it can be really rewarding once you get your head around the process.????‍♂️

Never took it off!???‍♂️

Two strokes and it’s gone!!!!!

Your cranks big end might have ‘felt’ alright on the bench but there are a few ways that the bearings can wear from barrelling to tapering depending on main bearings wear to! There was no detectable play in my crank but when taken apart there were some appreciable wear signs on the big end pin. Just replacing the piston will not solve the issue of piston slap, well it might but I doubt and it will be a costly mistake not to have a rebore and correct piston and rings. ?

So you need oversize piston to...if the cost is prohibitive to you then why not consider looking for a complete engine...or with a bit of research you may be able to cross reference the parts to another. You may be surprised to learn that not many bike manufacturers make their own pistons etc but state design needs to a piston manufacturer who then either makes or has a stock item that matches the design brief. This is how a lot of after market stuff gets into the market place. If you can make contact with a engineering company that does rebore work and engine overhauls, they might try to match up your original parts from information they have. If you are making the TLM into a 260 from 220 I think that was the original capacity you may well have to use a piston from another bike. The small/little end bearings are also mass produced and not just made for one specific type of piston, hope you are following this information as it can open up more choices to you, you might even find that costs to you are significantly less than those being bandied about by internet and other sellers. Obviously the aforementioned info applies to the piston rings as well, if not more so.??

You won’t find a new genuine seat, they are like rocking horse poo rare! They are not that complicated and to fabricate some out of metal would not be st all difficult. I got a very good replica (grp) with the right type of cover all complete for about £70 from Yambits they may have the brackets but don’t hold your breath. I took this route as all of the seat/saddle refurb companies that I cantacted either offered indifferent replies or were extremely expensive. Hope you have succcess. By the way the original Yamaha TY seat bases were not well thought out, if the seat cover leaked water into the seat foam there was no escape so it sat on the metal base eventually rotting the metal. Also the metal seat base is very close to the air filter cover inlet, any flexing in the seat base causes the seat base to touch the filter inlet which then bends and retsticts the air flow going into the filter housing; something to watch out for. This seat base flexing also causes cracks to appear if you are a bit heavy so ensure your replacement seat is correctly supported underneath. I’d be wary of any internet offered seats as they will invariably be rusted and welded up increasing weight and hiding nasty filler etc. You can find TY seat covers on the net and offered by some retailers but again be careful in making your choice.??

Strawberry juice clogs yer exhaust when hot and sticky.

Yogurt maybe

??‍♂️???‍♂️??

What no cribbing then either! ??‍??‍??‍??

From having had in my possession an ex ISDT Triumph a long time ago now, I can say that from a conversation that I had with Roy Peplow I learned this. There were 5 bikes specially built, frame number one was EXP 01 and this was the jig original. This stayed by the jig for assembly and fittings to be added or modified, the design buck in other words, it was not for use as a finished machine. EXP 02 was the build frame from which 3 more bikes were produced, EXP 03, 04 and 05. Roy was able to also inform me who had which bike, that they were all 500cc or there abouts and had Police spec exhaust cams. On the road they would all manage 100mph ( brave). He then told me he could remember all of this easily as he had all the details in a little black pocket book. At the time I was more interested in selling the bike having just put the bike through the workshop ( I took it in p/x as a non runner in bits against a new bike) as I was a bike dealer then, even the man himself Sammy Miller had a ride on said EXP 05 the bike in my possession. Having travelled a fair distance with the bike in my pick up all the way to Mr. Millers place in Hants, he confixrmed it as a factory bike but wouldn’t pay the price I was looking for so I returned to my shop and sold it the next week for £1200 (1979 prices). If only I knew where it was now? I add this factual story as an indication as to how a manufacturer might number their ‘specials’ .

My M80 frame number is about 30 numbers before your’s and the reg document states 1972 so we can accept that year as true?

My M80 frame has 4mm thick gusset plates and the frame tube walls are 2 mm thickness. But it’s not gas pipe or water pipe or conduit tubing either. How do I know, because one of the previous owners must have used the bike in a rock breaking trial and flattened the bottom frame tubes, so I cut them off and made replacements using 1.5 mm seamless tube. It’s still a heavy frame though! ??

I’d have said ‘developed rather than devolved because you now can appreciate the finer character in the older bikes. Some one who has and runs a Cub will probably be along to help you. Maybe you could ask the same question in the bike specific section of this website.?

Nearly all bearings and seals carry identification serial numbers eg 6203-56 etc. and possibly you already know this. Although there are many bearing and seal suppliers, Simply Bearings have been excellent in supplying me with all my needs they have an excellent website that allows you to compare and choose from top quality to lower priced components for application needs. Have you not kept the old parts to refer to? Take off the seal carriers and you may be able to identify the seals and bearings, I may be wrong here, either way I’d carry out a bit of a flush through to remove any metal particles if the bearings are seriously worn.?You could try Feetup Trial Sport e-bay store, they may give specs or supply if the prices meet your spending needs.

Well the bike looks good, some engines are quiet and eventually start to make noises. Some Bultaco engines were noisy from the start, luck of the draw on manufacturers accepted tolerances. As you identified over tolerance on the piston to cylinder bore clearance naturally it’s going to ‘rattle’. Your engine could go for some time before mechanical kindness kicks in, bear in mind that excess clearance will affect engine performance and it’ll not do the piston or rings any good in the long run. Better to remedy this sooner rather than later. If the barrel is on its original bore size then a reborn and piston to the next size or two up. Small increase in capacity will be an advantage but not by much. Try for a Mahle piston, not cheap but as original equipment OE depending on Bultaco Factory finances at the time your engine was made.

I’ve had a better look around the headstock, not just at the welds and frame number and guess what? In the same area as that G stamp I have the number 4 stamped in! Was this a way of the factory identifying which worker did what frame or was it an inspection stamp. Either way it’s intriging and now I to want to know what these extra marks are....now where’s that Mr. Miller??

Compression leaking out, or air squealing in or out from main bearing oil seals possibly. Have you only just noticed this sound?Compression leaking past piston rings as piston movement just stops....could be totally normal. In the quiet, ghetto blaster off, Chris Evans muted (gone would be better) talkative by standers asked to multiply 3.789 X 754.89 in there heads, and no calls from the kitchen about things not working...and you will hear all sorts of noises emitted by your faithful steed. If it were my machine and it worked as good as before the noise noticed then ignore and ride on???Your engine running will utilise the compression increase on igniting the fuel and air and this will force the piston towards the cylinder walls increasing the seal. That’s why when the rings are nipped or gummed up power loss is felt. The only other thing that comes to mind is the water pump seal may be squeaking, I’ve had no end of water pumps that make all sorts of noises straight out of the box. The lube contained in the anti freeze usually helps resolve that issue. Do you still run anti freeze in your bike? Any work done and you may have had tap water put in the cooling system. I always recommend using distilled water pre mixed with the best quality anti freeze you can obtain, less chemicals to attack the aluminium. Hope you can either eliminate this sound by finding the cause or satisfying yourself that it’s nothing wrong.??

Duff kill switch, been covered before about a week back. Reconnect ignition switch and confirm everything good. Test kill switch with a torch battery and bulb a simple circuit to confirm kill switch is good or duff. You could use a DVM to test the switch if you have one.

Hey where can I sign up for this Prancercise...that could be me late for the train or bog (no 2) or collecting my new Dizzy Trials (Vertigo) get it? I’ll get me coat shall I?

Ah now there’s a thought, rip out the antiquated chain drive, install a riveted leather belt with oversize rear wheel pulley. Slap an armchair where the saddle fits and a red candle complete with rustic candle holder to the rear ( not too close to the seat...elf an safety) oh and a white candle between the forks. We could all do our own Lundinium to Brighton run, sidecars accepted too. Anyone who owns a Bultaco Cultivator could enter as well obviously they have to accept the fact that they may have to walk there and back! If we ditched the spark plug and used the candle for ignition we could well meet that suggested 3hp?? Bread and gruel stops at the midway point.

No matter what it is the bike looks to be in relatively good shape and as you say you like it, so that’s a good thing. So what if the engine and frame numbers don’t match, it has an engine that works and a frame that is in god shape. I think you have a 158 frame which might have left the factory with a 325 engine in it and at some stage another engine has been put in. But you must bear in mind that around the 60’s and early 70’s it was the done thing for dealers to have two or more bikes of the same type and model, then remove both engines and swap them about. This meant that purchase tax was avoided as the none matching numbers allowed the dealer to declare them a kit form bike. This is just to indicate how you might end up with what you’ve got. The RM letters at the front of your engine number indicate R = 238cc engine capacity M = Motor and then numerals for production quantity. The 158 has a frame just as you have, it was the revised version of the M80 with additional side brace frame tubes. The letter R was introduced about 1973 when Bultaco started changing engine capacities to meet worldly demands etc so there will be engines with different capacities identified by a letter in front of the M. But that doesn’t stop people fitting different length conrod and pistons and barrels to increase or decrease engine cc. So the 1980 part of the engine number is the model and not s year designation, it’s an engine from a 198 whatever. Finish rebuilding/restoring it and enjoy, and as already mentioned earlier contact Dave Renham at Bultaco UK In Motion who will no doubt be able to help or point you at someone who can? Or go to Google and type in identify my Bultaco which should get you to Team Bultaco.

Get a go on another of the same and compare. It may be that there is a adjustment issue or the clutch may need stripping and all the plates checked for warping and rough edges etc. Not sure about the oil, but the manufacturers specification should be used on such a new bike. Maybe you need to go back to dealer and see if there is a warranty or rectification notification on this problem. I’m sure someone will be along soon with the oil type and fix for the clutch. ?

It’s about time a manufacturer got the gearbox output shaft a bit closer to the swing arm pivot, now that would make a real difference to both rear suspension reaction and engine torque reaction on said pivot point. Vertigo looks as though they could be getting close, although Beta may be nearer. Someone a few years back did this on a M/X bike with the swing arm mounted on two separate pivots...one each side and the engine gearbox out put shaft sitting exactly in line with the pivot point. Produced very little difference in chain tension through the full swing arm movement meaning chain tensioner could be virtually done away with, there was also reduced tendency to wheelie under heavy throttle unless the rider wanted to loft the front. One issue was that the frame was slightly wider around the swing arm mounts and more reinforcing was used. Any thoughts trialists???‍?

Better ride it very carefully then....or enter easy trials.