XJ900 YAMAHA/MGB-GT TRIKE

Construction Diary

Ok so I'm a bit late in starting this diary so ill put a quick note with the first piks and then continue from where I am now.

First I got hold of a Yamaha XJ900 which as usual I paid well over the odds for, but enough of that. I also spent some time trying to find an axle with the right kind of ratio in its diff and instead of paying well over the odds for a reliant one I managed to get an MGB-GT one for a fair price. The images below pretty much show what state the bike and axle were in when I got them and the last photo shows the bike with the plastics and useless parts stripped off.

The next task was to cut the back of the original bike off, however before doing this I made a stand I could put some screw-jacks on so I could setup the bike to make sure it was sitting level. Then with the bike on the jacks the rear was all cut away and the suspension was removed. With that done the axle was positioned roughly where I wanted it to go on axle stand. A quick clean and then I removed all of the previous mounts off it and spring cups etc to leave it clean for my mounts. Also a quick browse of eBay successfully scored me 3 cosmic slot-mags in good nick for £7.50 which was a fair bargain along with a trip to BME (Buzzard Motorcycle Engineering) and I got a set of 225/60/r14 cooper cobras fitted, which Ian had lying about spare from another project.

After looking at some of Ian's trikes, which have tubes welded to the axle which you then use to bolt through plates in the frame I thought I would use something similar to this but with machined lugs with an m16 thread in them I could weld to the axle and have the ends of the bolts hidden instead of using nuts to hold the bolts. After turning four mounts up I had to make the two plates which would be welded to the frame. These were made with some scrap 1/4" plate I had lying around. I then clamped the plates together and drilled two clearance holes in them. I did this at home so it involved drilling out at 13mm with my little pillar drill then opening them up with a cone cutter carefully, ok so a bit of a bodge but it worked. Then I bolted the mount lugs to the plate and positioned them on the axle, measured it out and welded each one on. To make the position of the axle plates and axle mounting easier I made four large washer/spacers up at work with the same internal diameter as the outside diameter on the mount lugs. These where slotted over the lugs and the plate bolted in place. Finally I welded the washers on, this should take some of the shear stress off of the mount bolts now and I have also replaced the high tensile galvanised ones with some nice spangly stainless cap-heads

With loads of holiday left to book before Xmas I decided to book off a week in late November and spend it blasting away at the frame and hopefully get it rolling. A quick trip to 'Steel-Fast' just outside of Leighton Buzzard returned fifteen metres of 3mm thick inch and quarter OD tubing for £30 which is plenty good for me. After making a metal rack to hold all this new metal I got to work making the frame. I started by properly aligning the axle with the bike, I have no photos of this so I will try to describe it simply. First check the axle is level by putting a bit of straight wood across the tyres and using a spirit level on it then level it by shimming it up with hardboard or such. Using a bit of tube against the inside of each wheel (must be raised so its touching the front and back of the tyre) on the axle which extends to the front of the bike. then measure the distance from the tube the front wheel perpendicular, doing this enables you to move the bike until the front wheel is central two the rear two. Then check the bike frame and move it so its central as well. finally as a last check measure from a datum point on each side of the rear axle to the head stock this should be equal for each side. After a lot of fiddling about and its in the right place make the frame! This was done using a hydraulic bottle jack type bender which can be found in the machine mart catalogue. I made gradual bends by marking the top of the die and then marking the tube at half inch intervals and using a few pumps of pressure on each mark. After making the frame pieces and making sure they are the same I notched them to fit the bike frame. A quick check the axles still in the right place and I tack welded the lower tubes in place. Then I made the other tubes and tack welded them in quickly checking the axle hadn't moved at regular intervals.

With the axle made it was time to consider getting the prop-shaft made and out of the way. I emailed a company in Luton but they wanted well over £150 and this project is supposed to be on a tightish budget so I concluded I would have to make it. I did this very simply by cutting an MGB prop-shaft in half and fitting the original bike one into it. The 3D render you can see has been cross sectioned so you can see how did it. I turned up two slugs which were both a press fit into the MGB bore and a press fit onto the XJ900 prop-shaft (Note if you want to do this make sure you put two small flats on the outside of the slugs if the prop-shaft you intend to press them into is made from seam welded tube otherwise you will have one hell of a time getting them in). I then welded the spacers to the XJ900 shaft pressed it into the MGB one and welded it up. I also drilled two holes opposite each other in the rear of the shaft so I could weld the spacer inside to the outside of the prop-shaft. Finally I changed the rear trunion and caps as the one in the unit when I got it was a bit lumpy and it was a nice cheap fix.

With it at this stage I wanted to get all of the welds fully welded up and neatened a bit and get all of the mounts off the frame I don't need such as body panel mounts etc. Firstly I took the engine out for its rebuild (more on that later). Then I took the forks off and got most of the rest of the welding with the axle still holding the rear frame true. I had to remove the axle get to a few of the last welds but I got as much as possible done with the axle on to hold it square and true. With the frame welded the axle was removed so I could clean it up a bit better and sort out the rear brakes.

With the engine out of the frame and seeing how it had been standing for such a long time I decided it would need a rebuild. After following the Haynes manual carefully I had the engine stripped enough to realise its going to need a fair bit of tinkering with. The barrels had corrosion at the top and the valve seats were pitted. Anyways after a few trips out for some more specialist engine building tools I now have a valve spring compressor and a cylinder hone. I have probably committed some nasty crimes in engine building but the barrels are now free from the oxide you can see in the photo bellow, and the valves are all lapped in lovely. IMPORTANT: if you intend to strip the head on an engine like this make sure that you carefully store all of the valve gear so the valves, shims, cam followers, springs and camshaft journal caps all go back in the exact same place you take them from otherwise you will find all the tolerances are off and you will need to spend serious time setting stuff up again and if you put the journal caps back in the wrong places you could cause it to seize if they have worn unevenly. Well after another trip to BME I managed to source a fair load of spare engine parts from an xj650 and a 750 to get caps and covers from and the odd pin here and there. The engine is almost complete now minus the electrics. The last photo shows the two carbs I have got round to cleaning up. The other two still need a good scrub. Then I will get to work on the insides but its not looking good as all of the diaphragms are split on them which looks expensive. Well the engine will go back together next week when the new gasket set comes in then I can start grinding on the frame and dressing it up.

Whilst waiting for the engine gasket set to come in I drilled out the broken studs, from the head. This was a job I was a bit reluctant to do as I didn't want to scrap the head but it came out, just had to take my time and be careful and not rush. With that done I fitted a wire brush to my dremel and cleaned the whole of the outside of the head up and then cleaned it out with an airline and gave it a dunk in a solvent tank. Before fitting the head back on the engine I had to fit the valve gear back into it. To make sure the valve guides were free from dirt I pushed a pipe cleaner twisted round through each one. Then I cleaned the valves and springs up as they had gathered a bit of dust from standing whilst I was doing other bits. Finally I fitted each valve back into its respective position in the head. Using a valve spring compressor which I bought at Halfords made the job a doddle which only took about 45mins, the final photo shows the collets being fitted whilst the spring is compressed. I filled some burrs off the valve spring compressor to make sure that if it did touch the side of the cam follower way it wouldn't mark it so easily.

With the head rebuilt and the gasket set in at last it was time to build the engine up. The new cylinder barrel gasket was fitted along with new seals on the oil ways. After feeding the cam-chain through the centre of the barrels, I lowered it on the studs and onto the pistons, carefully pushing it down square and making sure the rings tucked into the lead-in on the bottom of the liners. Once the barrels were sitting on the crankcase I gently tapped it down onto its dowels with a leather mallet. Then the head-gasket was fitted along with new O-rings for the YCIS passage and more o-rings for the oil ways. Then remembering that two of the dowels had been left out of the top of the cylinder block by the previous owner I had to source some replacements. The shagged 650 head I had gave them up, after drilling the bolt holes out so I could get a drift in to punch them out they were fitted to the 900s cylinder block and the head was fitted down onto them and locked down with all of the 12 head bolts and torqued up to the correct setting in the right order.

The camshafts were put through the cam chain and with the engine set to TDC I lined them up in the right orientation and fitted them into their journals fitted the cam caps and double checked the alignment and fitted the cam chain sprockets to the camshafts and torqued everything up (I also fitted the cam chain guides and cam chain tensioner at some point in there). The second photo bellow showed the centre cam caps of which you can see three were cracked around the thread were they had been stripped and heli-coiled in the past. I managed to replace these with some I picked up from BME. Much nicer and as the centre caps don't have cam journals in them its safe to change them without any worry about uneven wear.

Stupid me for not checking earlier but when taking the clutch apart I checked to see if the bike went into each gear nicely. I soon found out that 4th and 5th were missing... bugger, my opinion on the bloke that apparently rebuilt this engine is seriously low. Silicone sealant is NOT our friend and does not need to be used on every gasket surface and "do it an extra turn tight to be safe" is not actually safe, manufacturers give you torque settings for a good reason!

Well the only way for me to find and fix the problem was to pop the crankcase/gearbox apart and take a look. So after removing the 40 odd bolts that hold it together and the other little bits such as the ignition, gear selector mechanism, the rest of the clutch, final drive parts and the oil pump it was separated. Instantly I could see the problem, he had forgotten to or not bothered to make sure the middle selector fork had located into the output drive shaft when joining the halves back together (the stupidity here is not that he did it as its easy to do, but he didn't check he could select every gear when he had put the halves together and then realised) Anyways whilst the halves were apart, I took the opportunity to clean out all of the crap from it and remove all the silicone sealant from the oil ways and check all of the bearings. It was then put back together with a good clean matting surface (stoned down with an oil stone) and a proper gasket jointing compound used very sparingly. The halves fitted perfectly and with the gear selector fork engaged all of the bolts were tightened in the correct order and then I refitted the middle drive shafts and checked and set the shims a bit tighter on them as they were looser than the specs required.

With the crankcase halves together I refitted the gear selector mechanism and checked It hit each gear, which it did perfectly. Then I turned the engine round and cleaned and refitted all of the clutch parts as they were all fine and the friction plates had plenty of meat left on them. The next job was to check all the valve clearances, I managed to get hold of a shim changing tool off eBay for pretty good money which makes the job of changing the shims really quite easy. Firstly I checked all of the clearances with some feeler gauges (this was done with the cam lobes facing away from the followers) and noting the clearance for each valve down on a chart I drew up. Then the ones which were not right (all of the buggers) needed changing. To do this I simply wound the engine round by using a spanner on the ignition timing hub until the follower was pushed down by the cam, then I fitted the tool and wound the cam back round, the tool held the follower down so that I could pop the shim out and check it against the shim size chart and put a different one of the right size to bring the valve clearance to the right gap. With a new shim fitted the cam was wound back onto the follower and the tool removed. NOTE: you must be careful not to wind the cam round into the tool otherwise you may damage the crankshaft or break the side of the head off as the tool fits very closely to the cam. The centre photo shows the tool fitted with the cam follower held down and the new shim ready to fit (after oiling also note the shims should be fitted number side down). Finally before giving up for the night I fitted a new oil filter.

Whilst I'm still trying to find the ancillaries for the engine I've done some basic work on the frame, a bit more grinding and dressing of welds, including removing the centre stand mounts which required delicate hack sawing and filing of the frame. I also replaced the lower frame rails as they were being eaten away by rust and I don't like it when I can poke a screwdriver through the frame. To do this I bolted in the two gearbox halves from an XJ750 I had to hold the frame in the right place then cut out and replaced the rusty section with a new bit of tube.

After a good delay I finally found all the bits I need to get the engine running from a nice chap in Wales. And after exchanging some notes I now have a complete early XJ900 engine with all ancillaries in my possession. Although its an earlier 853cc version not an 891cc like my current engine it does have the earlier loom and TCI which has not got all of the side stand safety bollocks on it etc so after I get it up and running I intend to try and swap the running gear to my engine and see what happens. I just need to check a few things and hopefully will have it running this week.

anyway here are a few photos of it with the manifolds fitted upside-down so they don't hit the bench. (I may get round to adding a video if I get it running this week.

With all of the bits ready and a bit of help from Dan I have a tiny little custom loom to run it and a quick exhaust made from pipe and duct tape we have a runner!!!! anyways see for yourself by downloading this video (right click and save as)

With a running engine my enthusiasm was returned to the project and I spent a whole week of evenings grinding welds so I could get it put back together on my week off. I also managed to get the top yoke milled, as the standard XJ900 top yoke had teeth on it to locate with the handle bars. As I'm going to fit risers I decided it would be best to remove the teeth. Ten minutes on a mill later and we are all sorted.

With the welding and grinding all touched up and nice I decided it was time to put it back together and get it looking like a trike again. I chose to put the spare 853cc engine in so that I could make the exhausts etc and grind near it without worrying about getting dust on my rebuilt clean engine. Plus I need to work out how to get the engine in and out without scuffing on the frame too much. With the axle on, the engine in and the forks on and most of it back together I made up the exhaust system using some 2-1 adapters I made from some mild steel sheet bent around into a cone then flattened at the large end. The original down-pipes were then fitted into the cone and welded in with a cherry bomb fitted to the other end... simple short exhaust system which should sound rather nice when finished.

Finally before packing up for the day I decided to make some heat shields for the cherry bombs out of some drilled brushed stainless sheet I had. The shield is spaced from the silencers by the width of an M6 nut which is welded to the silencer. The shield then fits to the silencer with three counter-sunk Philips drive stainless screws. I will try and replace with ones with Allen heads if I can find some.

After a bit of a break from the trike working on the cb125 and then suddenly noticing how close the sodding deadline is I thought it best that I get working on her again!! so without further ado the action plan was to start working on the fuel tank as it involves a nice bit of fabrication and I haven't done any major fab for a while. First things first were to remove the feet from it which I didn't need. As you have probably guessed it was an air receiver in its previous life! With the feet removed it was a simple round tank. I rotated it so that the most open pipe fitting free space was facing the top with the welded seam facing where I wanted the bottom lip of the lid to sit. I then secured the tank to the frame with tape top stop it rolling off for a second time (good thing its thick steel otherwise it would have dented badly) I marked out the hatch size so that the hatch should open and rest up without having to be held. I found the thinnest cutting discs for my grinder I could and cut the lid out. With the lid out of the way I could clearly see the inside of the tank and what space I would have to work with for the electrical box. I made a mock inside from cardboard which will also work as a template for the real one when I make it. this is as far as I have got.

Today I got the side pieces for the tank done and started work on the battery compartment. Hopefully I can finish up welding the battery box tomorrow and get some more sheet to make the main base.