Not Starting

[fastharry]

Is there any way of testing the red pickup on a 350s. I have a spark but its redish colour. I have changed the stator plate for one with a rewound coil thats giving 220 ohms. 188 ohms on the old one,
I have not got a spare red pickup. only black one, i have the transducers to match it on another bike so eventually i will swap them all over, i noticed the ignition coil was in a different position on the plate, but i doubt that should effect anything? I have now worn my right knee out trying to start it. any ideas chaps,

[72degrees]

Is the rotor still well magnetised?

Worth swapping the black pickup in and just one later transducer jury-rigged to see if that improves the spark? Or perhaps try one of the cheap 'Vespa' transducers on offer on Ebay.

Check the earths on the transducers and that there is a dedicated earth cable from the crankcase to the frame. On a 250 it is easy to make that connect on the same point as both transducers. May be possible on a 350 with a longer cable.

So the ignition winding on the stator is in a different position to the one you removed? The yellow ignition winding is usually at about 3 o'clock. Is it significantly different to that? I can't see it making a huge difference but evguru will probably be a long in a while.

[fastharry]

Thank you for the reply 72, What i forgot to mention is that i had gone down to a 40 pilot, Someone once said 7/10 's of ignition problems are down to the carburetor , I happened to find a previous right up on jetting, and he mentioned not to forget to turn the mixture screw out to compensate for the smaller jet. 3/4 of a turn later and bingo she fires right up, several hours wasted plus a right knee like a cabbage, + plus a quick email to cancel my cancellation to the race organiser, and im feeling a bit silly, So there you have it , an idiots guide to fault finding,

[72degrees]

Glad to hear it's cooperating now. I think sometimes a combination of things leads to poor starting. If the spark is tip top a slight carburation problem won't matter. If the mixture is spot on a less than perfect spark won't matter.

[fastharry]

Ive worked on a lot of bikes, but Morinis seem to have a few isms. I have started on a 507 engine from a custom excaliber i think its called, i am about to fit a needle roller main bearing instead of the bush. Would you recommend any particular cam suitable for dirttrack racing, perhaps similar power to a hill climber would be about right, Also i noticed a lot of people knocking the 501 engine, is the 507 much of an improvement? I do not want to spend to much time on it if not, I converted the 350 into 400 with polo pistons + a bit of gas flow, and open pipes, i have to say im very impressed with its turn of speed, considering it has standard valves, i was thinking of changing the heads to improve things further, any thoughts on that?

[72degrees]

I have no experience of any of the 500 engines so can't comment. As to cams, by far the best of those I have tried on 350s has been the L5. I may go so far as to swap the 350 top end on to the 375 with L5 for next season (to stay legal in the 251-350 class). None to be had for love nor money though.

Apparently 500 heads can be fitted on a 350 if you relieve the cylinder liner to clear the bigger valves so in theory you ought to be able to get them on to your Polo piston 400 perhaps. The 501/507 thing confuses me as I thought the '501' was actually 507cc. No idea if you could graft the heads from the Excalibur on to the 400 but might worth "offering up" one.

I have a spare pair of good 350 heads (better the the ones currently fitted) that I may spend some time optimising to fit as part of the winter fettling and swapping.

[MickeyMoto]

The 501 and 507 are probably the same thing. Possibly a trademark issue? Nikasil barrels, earlier ones came with Ducati ignition later with Kokusan and different electric start out front. Probably other changes a rivet counter could explain.

Cams were different in Camel and Excalibur I believe. Probably want a Camel cam. The Excalibur has good low end. I believe the valves were further apart in the 501 head so careful on an earlier barrel.

[harrymuffin]

I see you used Polo pistons on your 350, has the engine stayed together? Are the gudgeon pins desax on the Polo as people in the past have tried using pistons on the 500's from other engines with central gudgeon pins to increase the size and could not understand why the big ends would last less than a thousand miles.
If you need grunt as opposed to screaming power revs as on the JAP and Jawa engines, then I would recommend the sport camshaft for the 500 as it has a not too big an overlap, has longer duration opening and a higher lift and with 28mm carbs the gas speed will be high as the engines were originally designed for torque and the maxim 'high gas speed equals high torque'. Anything bigger then the engine will bog down and only start pulling above 5500-6500 with a narrow power band. The 500s achilles heel is the big ends as they are at about the limit for size and loading as standard and especially so if you constantly use a lot of revs. When you build the engine, see if you can get a set of big end shells from the FIAT Multipla from the sixties as these are slightly wider than the Morini shells so reducing the loading on the bearings, plus if you can get Glacier ones then they are much better quality than those made at present. You also get four sets for the price on one half shell from NLM.

[fastharry]

What do's desax mean? I used Nural pistons. They have held together ok after a good ragging in 2nd or 3rd gear on Uk speedway tracks, The performance for a 400 has surprised me, I had a sprint race on dirt against a 400 maico crosser at the Malle Mile event, out of the gate he had me, but i got her into 3rd and i blew his doors off! But i would like to give the 507 a try for next season. I think the longer stroke will suit the loose tracks better, I have what is described as an L5 cam, Bought from Paul Compton at Stafford a few years back, I heard later that they where still under developement when i bought it so i will have to get it checked. I will put an add up for a Sport cam, I have to say the 400 with the sport cam pulls from nothing once you get the carbs set up right, I dare say the 400 could be developed further with some 500 heads and bigger carbs, but i will try the 507 first, I bought some shells from Nlm as i just could not find any Fiat ones anywhere else at the time.Have anyone got an alternative source? They are the wider ones that they had bought from a dealer who had a load of New old stock ones, I am also doing the main bearing conversion to roller bearing. One of my biggest stumbling blocks at the moment is what ignition to use, i have a Kokusan one but they need a battery and im not keen on using them when racing. I am going to try and get it into a 250 frame with a bit tweaking possibly , Any further performance / longevity tips are always welcome.

[harrymuffin]

De sax means that the gudgeon pins are not in line with the crankshaft, so if you look at the side of, in this case, any of the Morini pistons the gudgeon pin is off set from the centre. I think it is 8mm and was done so that the camshaft would fit in the vee by moving the cylinders outwards - like 'man spreading', rather than have the camshaft as on a JAP or Harley Davidson or a Vincent. If you use a piston without the offset in a bore with the the cylinders not inline with the crank, then it puts undue load on the pistons and big end, the offset gudgeon pins will be inline with the crank and so the loads will be directly inline with the crank and not to one side. Some engines other than Morini have been designed to have the cylinders offset from the crankshaft for various reasons, Sunbeam cars on their Coupe del 'Auto GP cars of 1913 had off set cylinders and so did the engines fitted to Land Rovers, but no idea which engines they were. I only know this because a chap I know has the works Sunbeam and was stuck for pistons and only discovered the Land Rover piston had the right amount of offset, plus they are made of aluminium rather than cast iron of the originals. I have offset conrods on one of my engines so have to go in the right way or the crank itself will break up once the corned has snapped. Omega Pistons of Blackheath made oversize pistons for the 350s in the seventies for The Tamworth Morini dealers Devimead (they moved out to Aberystwyth) but the racer was plagued with big end failures. They still had the dies when I got them to make a load of 500 pistons for myself and others in the club, with narrower rings and no split skirts.
The problem with taking a strada camshaft and regrinding to give more lift and opening is that a) you do not know how deep the hardening is and b) the bottom radius is reduced giving a a much more violent initial lift which causes a greater load on the valve gear. With camshafts from car engines or most engines designed way back, they had relatively, to Morini camshafts, large base circles so you could regrind without too much worry.
If you have decided to fit the roller bearing which incidentally was dreamt up by Ade Crimp and me - he did all the work I just found the right bearing to use - then unless you are striving for the last once of power it is not worth the bother. 1 to 11/2 bhp would be your estimated gain, but if you really go down that route then don't bother with grinding as you can turn the journal down now quite easily with special tips in the lathe which are designed to cut hardened metals, I know this because a mate of mine is the rep for Mitshibishi cutting tools and he gave me one to try. Ade did his conversion at work with a normal cutting tool, it just takes longer but quicker than grinding and if you are any good at turning then you should be able to turn to within 1/2 a thou or less.
Having been on the dirt track fringe in my youth then you certainly do not want a screamer, the people I knew then tended to use at the most three gears, ok they only had four, but the engines were all built for bags of torque through to the rev limit rather than all or nothing narrow power bands. I would have thought with the 507 engine with cleaned up ports narrow or radiuses valve seats, long induction tracts with K&Ns, short open pipes, it would go like shit off a shovel. I thought that the engine you have has a wild cam in as standard anyway, but I would still go for the sport cam. I have a 507 top end on a five speed bottom end and deliberately kept the 500 cam in and it developes it's urge at about 5000 and keeps pulling up to my own imposed rev limit of 8000, so did not bother stripping it to put the sport cam I have and was going to fit. I but it so that I would not have to play the organ with a narrow power band every time I had to knock off a bit a speed in a bend but could just open the throttle and she would recover quickly. The engine will fit into the 250 frame as all the crankcases came out of the same die molds, you will have to cut and move back the return tubes that loop under the engine, I did this on the 350 frame so I can get the rear head off if need be. Personally, I would build up your 507 engine and try it in the bike you have now, gear it for 8000 on the long tracks using 3rd, 4th, and 5th and try then assess your next moves.

[fastharry]

The offset pin is a bit concerning, (i was hoping to build a tarmac racer if the 507 proved to be ok). When i posted about this conversion nobody said a thing about it, at least the 507 pistons are original. Do you have any thoughts on ignitions? as i prefer not to use a battery as you have to with the Kokusan that came with it. I have a J cam which is not as good as the sport looking at the numbers, but not far behind it, Do you no if they ever got to the bottom of the bigend problem at devimead? The so called L cam i have do,s not appear to have been ground off at the base. it looks to be from a j profile from what i can make out from whats left of the letter, The crank has been ground by a mate of mine so that is sorted, Do you consider the plain bush good enough to race with? Thanks for all the tips and info so far,

[72degrees]

I find the NLM module used with XV250 coils and an OEM type 2 red pickup works well (no battery required). When I next get to a dry hill climb event I'll be able to tell better whether their 'performance' pickup adds anything to make up for the higher kickstart speed required to start.

[harrymuffin]

Regarding the off set pin, the force on the piston owing to combustion is resolved into two forces, one down the conrod and the other into a side thrust. If you remember back in your school days and the topic Vectors and Space diagrams then you will get a triangle of forces so that you have the top of the piston force, force down the conrod and the force between the piston and the cylinder wall known as the side thrust. This side thrust does no work and detracts from the force down the conrod which causes the turning force and hence power. As already explained why the Morini cylinders are off set from the crankshaft, this offset has to be compensated by moving the gudgeon pins back in line with the crank shaft hence they are not in the middle of the piston. If the gudgeon pin is left in the middle, as in your engine, then the thrust force is increased putting extra load on the piston and reducing the force down to the crankshaft and hence premature failure. I am interested in how you maintained the squish band and combustion chamber in the piston. If flat then then you have a large area for the flame to travel and negating the small combustion chamber as designed. Even diesel engines have combustion chambers in the piston with the gas being squished into a small area and so a quicker burn. What theoretical compression are you achieving as the sort has 11.5:1 and with a different piston it is going to alter and with your centre line gudgeon pin the actual will be lower I surmise.?
I made two models yesterday one with the Morini set up and an exaggerated one with the gudgeon much more out of line. It shows that the piston is well down the bore before it starts to do any real work without having to do any calculations, and the system of 'linkages' are obviously at odds with one another even though it works. As happened to the chap who built the 550cc engine, I think he used Guzzi pistons which even if they had a offset gudgeon pin unlikely to be that of the Morrini engine the forces were too great and it failed.
If you are thinking of fitting the 500 heads to the 350, I would suggest that you check the overall distance from the outside of the valves as it maybe more than the 64mm of the cylinder. This was discussed way back and it was a problem then. With 'big bore' engines now 372cc the valves may go down the cylinder but I think the Darts had 400cc barrels so they may solve your problem.
The Devimead project engine crankshaft was never resolved even when a built up crankshaft was designed and made. On hindsight, I think the problem was that the crank pin was not big enough (432cc?) and so overloaded hence the 35mm diameter on the 500's which I personally think is just about on the limit for higher power outputs with longevity in mind. I rebuilt more 500 engines than 350 engines with failed big ends even as standard.
The Benjy Straw racer I had, was bought off a chap who was in the Forgotten Era championships, bored out to 372cc and went like shit. I could lift the front wheel without having to pull on the bars when the power came in with a bang at around 6000 and would rev up to 10000rpm but he was always out classed with the full 400cc Jap crap available plus the Yamaha 2-strokes. No idea what the power output was, but probably put out more than a 350 Beart Aermacchi I had in period. The difference was that the Aermacchi was quicker per lap at Cadwell on the only track day I did with it, sold it to a plumber in Norfolk for track days.
The plain bearing issue, ask yourself why? The plain bearing is perfectly ok even if you intend to thrash it, plenty of bearing surface, well supported journal perhaps saps a bhp or a half over a roller, palaver of turning the journal down. Unless you are in a 500 GP, the journal is worn and you need to extract every little bit of power then build up you first engine as it is and perhaps get another crank and convert that one at leisure i.e.; don't make work for yourself as a lot of people seem to do on the forum. If it ain't broke don't fix which brings me onto the ignition. If you can find the thread on ignition you will see that I made up a copy of ignition transducers to use MZ 6V coils. It was at a time when spares were getting hard to come by and was for insurance to keep the bike going. I have let a chap in France have three pairs of circuit boards to continue with the project with the suggestion to substitute the fixed resistors -56ohm and 270ohm -to a variable resistor so you can fine tune the ignition curve. Hopefully he will report his endeavours on the forum.Now, I have 350 transducers on my 507 bike and have also had correct 500 ones on too, to see if I can tell the difference. As long as the 350 ones have the same advance at 6000rpm on the road I cannot tell the difference. Perhaps if on an engine dynamonitor and tested properly you will see a marginal difference, but trying to measure on the road is not easy. I do remember afternoons spent on the Meriden bypass with the Police watching and chatting, setting up the ignition and carburettion upon a cammy Velo where you could tell if there was any difference especially when with a friend on another bike that was not being fiddled with. I see nothing wrong with the standard ignition system and see all these comments and queries and regard that people are just trying to find something wrong with it. If the same systems are fitted to Rotax twin cylinder engines that power microlights then if passed for flight then they must be good enough for a cooking Morini engine. There was at one time probably half a dozen different after market ignition systems for the Morini, I still have some of the adverts but again my mantra - don't fix what ain't broken. Why make work or invent problems that do not exist . I admire you endeavours, as what you are doing, it not only develops the mind but also expands it, but don't get bogged down with the minutiae such as 'what tyre should I use?' or what plugs are best? they are all personal preferences adopted through experience I only wish that I still had the motivation to keep on solving problems that you have , but having been there seen it and others making cockups, now prefer to potter and lose my temper when things that should not go wrong do. If you can get your hands on the club magazine form the start, then a lot of the current topics have all been covered before, unfortunately I sold all my stuff off not very long ago; I am sure one of the geriatic members still have all their copies and may let you read them on the forthcoming long winter nights.

[72degrees]

I had my roller bearing conversion done while NLM were getting the crank reground (plus new rods) as the plain bearing was fubar anyway. I wish now I'd also gone for their cunning 'circlip' mod to allow easy cam changes without splitting the cases. On a direct, back to back, comparison with each engine in the same machine (the 1980 road 2C) last October, running the same ignition system (NLM module and 'scooter coils), exhaust system (NLM 2:1) and carbs (PHBH28) the difference between the '375'/L5 and 350/?L regrind was very significant. Not all down to the 22 extra cc I reckon. I'm pretty sure I got the mystery cam in the project engine timed as best I could using the vernier pinion, but it doesn't rev out like the 375, even now the carburation is pretty good, at least WFO. The ultimate test may be performed next season by switching the top ends to make a 350/L5.

There was nothing wrong with the standard ignition system when the components were new. After getting on for 40 years it's not surprising some don't perform brilliantly now. With all new replacement parts to the same specification it would be fine. I'd really like to find a supplier of replicas of the OEM type 2 red pickup as I'm not convinced the independent timing feature of some replacement types is as significant as claimed. What I have done, is run the same machine on an NLM box/conventional HT coils and then OEM transducers back to back. The transducers history is unclear but despite spending years in a barn - it was a probably fairly dry Spanish one. The NLM setup definitely starts more easily and a lower consistent idle can be obtained in my experience.

The variable resistor idea sounds cool. A bit like the 'mapping switch' on KTM 2T CDI's that just switches in different resistances to alter the curve. I used it at a very wet and muddy Wiscombe track on Sunday to tame the KTM250 down from 'wild' to 'mild' - then I probably should have also swapped the power valve spring for much more effect

As so often has been stated, the heart of the ignition system is the stator winding and rotor. I'd always advise anyone to spend their cash on a rewind and rotor re-magnetisation before anything else unless it they are absolutely 'known good'.

If I remember correctly Benjy Straw ran 500 heads on a racer but as I think evguru still has them presumably not on the 372 version you acquired. It was Paul that mentioned relieving the bores to accommodate the bigger valves.