Hitchcocks Forum

The more I try to learn about dealing with my Bullet engine, the less I know. HELP!!!!! I keep being told that with a higher compression piston fitted (in my case, 500 bullet) one must retard the ignition accordingly. Fair enough. But is this a trial and error scenario, ( equally being informed that each bullet engine has its own vacarious needs and wants) or is there a formular--e.g.; 2 degrees. And then,how would that translate to movement on the points backplate? At a certain point, the "retardation " is going to apply the spark after TDC, surely? in which case is this OK?.....................On a different subject, but related to my situation I'm trying to sort out----when a piston starts to "pinch up" on the cylinder wall, precursor to siezing presumably, WHAT NOISE WOULD THAT INCURE? In my case the engine continues running after one of these "attacks" seemingly normally. That's what I'm working on eliminating, with your help..............?

Al, I don't think that the timing will be the problem in this case, as long as it is set to the original settings, more likely it is the fuel mixture that is now weak causing the hot running and the piston nipping, there is no sound that warns you of this you just feel the power decreasing, try raising the needle one or two notches this should make it run cooler.

The bullet motor is no different to any other four stroke motor in that all the principles that apply to any motor apply to them. There is no secret trick but it all sounds confusing and contradictory in one indigestible lump. Timing first: you need to retard the ignition slightly for a higher compression pistion. This relates to the point at which the points open on the compression stroke. So first you need to establish TDC on the compression stroke. A thumb over the plug hole should tell you the compression stroke and a stick down the plug hole will tell you TDC ( top dead centre) the setting for the 500 I would guess is standard somewhere around 1/2" to 7/16" before top dead centre so the place to start seeing as you've raised the compression would be the 7/16" side of the ledger. Get a piece of stick and a sharp tip felt pen and with the plug out establish the highest point of the piston in the bore and mark where the stick touches the side of the plug hole ( any old piece of wood eer a pencil will do) . Then measure with a ruler 7/16" back from that on the stick and mark that point with the pen. Noe you need to turn th.e bike over ( selecting a 4th gear and using the back wheel can work well for this process) turn the motor over soit is on the compression stroke ( thumb over the plug hole) and then stop when the stick reaches the new mark. The points now need to be set at the just opening position with the distributor bob weights in the fully advanced position. I haven't got a battery and coil bullet but I assume if you cut a small wooden wedge you can probably prop the bob weights open. The points need to have been set so they open to a maximum of 12 thou in any position on the cam and then taking the direction of rotation into account the points plate needs to be adjusted so that the points are just opening at the position you have set the piston at. A cigarette paper works ok for this. Clipped between the points you adjust until the paper just starts to slip. A low tension light or a multimeter are other ways of establishing this exact moment when the points begin to open. Once this is done you remove the wedge from the bob weights and put all the covers back on the the plug and lead back on. As for the piston pinching, you can only tell for sure by pulling the head off and checking the condition of the bore. It maybe that you had a slight nip and maybe it was just the leanness of the carb starving the engine to the point of failure. Whatever I'd get it running right and see if it makes smoke or lacks compression before I'd stress to much. A total seizure is something that can't be ignored but a slit nip might not have done too much damage and if it has you'll find out soon enough and you'll need a strip down. Don't stress too much this is all supposed to be fun! S:)

Good advice and descriptive info from Simon. Yes higher CR's requires less ignition advance to avoid pinking. Just to add that to RETARD the ignition....Rotate the points backplate CLOCKWISE....To ADVANCE the ignition: Rotate the backplate ANTI-CLOCKWISE. NB: Every ONE degree of rotation on the plate equates to TWO degrees of crankshaft rotation. As you have been told by others....every engine/ fuel setup is different which means the OPTIMUM ignition timing will vary from one similar engine to another. This can be set by adjusting from the "nominal timing" by ear by setting the timing just BELOW (Retarded)from the point where the engine "Pinks" when under heavy load. Partial siezures are still seizures which means some amount of metal has been abraded away from the piston, caused by actual metal to metal contact between itself and the cylinder wall. Once this happens it is quite common to experience more piston slap noise as the piston clearance has been increased. Cleaning up of the scored piston only increase the clearance even more unfortunately. It is annoying but the only thing you can do is to find a new barrel which is tighter fit to the piston and this can be cheaper than buying a new HC piston if it is an Indian model, otherwise one just has to get used to the extra clatter

Al. Sorry to hear of your seized high comp piston. I put one into my 1996 500 with teh correct clearance.
And seized, and seized and kept on seizing, no matter how carefully I treated it. Later I realised that such a high comp piston (our hosts 8.5:1 forged) didn't like the cast iron barrel so I bought an ally one. Can't say that made any difference because I also changed the piston. Its not the rings seizing, its the piston itself too. In fact it even seized when I had filed off the rough bits, honed the bore and had a clearance of ~12thou!
With regards to the timing, a movement on the circumference of the points plate of 1mm (it turns at at half speed) equals about 2.5degrees true. Not many people know that. Alternatively, get it roughly right and then fiddle. Then go and ride the BMW.
Cheers
ChrisD
Not much help, I';m afraid and I'm stuck here in cold winter (well its below 20degC) with a prolapsed disc.

Hello AL --- To the uninitiated this terminology of "Advanced", "Retarded", "Pinking" "Compression Ratios" can seem daunting at first. But don't worry--well, not too much at any rate because you have 2 major tools or assets at your disposal viz}--1)The combined and varied expertise from the lads on these pages and ---2) GOOGLE !! There's bags of info out there on the wacky, world-wide web. Just be inventive as to how you title your request. I take your point about retarding a timing setting that is almost at TDC anyway ( some high speed diesels have a 2-stage injecton process of before AND after TDC)---however that is the STATIC figure that most people tend to use for setting (0.7mm for the 500cc) whereas the professional will seek to use the DYNAMIC figure ie when the auto-advance, activated by the engine's movement, has altered the setting to the FULL-ADVANCE position that is now required. This is what SIMON is referring to and can be achieved by holding the bob-weights open artificially. Our hosts supply a purpose-made taper ring for this . See}-----HITCHCOCKS
PART No. DESCRIPTION PRICE
49717 AUTO ADVANCE LOCK WASHER TOOL £1.50 ----------------------.This method also takes into account any mechanical wear on the stops etc. If you want REAL stories of piston seizures, piston slap etc have a word with any BSA Bantam owner or the like. Those of you who know Portsdown Hill by Portsmouth, Hampshire will sympathise with a very young ALAN R bringing a 1950's Bantam 125 3-speed ( two-up)up that incline with 2 partial seizures and several "Whiskerings" before we even got to the top !!!!!!!It went like this}---seize up, stop, sit down, smoke a fag, start up,--------seize up, stop, sit down, smoke a fag,start up----etc. I quit smoking years ago(Ex-RN) and, hopefully have quit seized pistons as well. Also---the quality of the fuel in use will have an effect on ambient eng. temp. etc. Have a look for yourself as to the difference between "Pinking" and "Knocking"------------- Be seeing you.

Well lads, this is another 3 pint topic! Once again pleased to meet you all here, thanks for input. As Mr. Mannering would say (to me) --"don't panic". Anyway, I'm set up now for a test session tommorow, plug chopping and timing tinkering. Having studied all the posts and read host's tech page I've confirmed I'm not as ignorant or confused as I thought. There is always the possibility that this engine will get its original piston back and be a reliable Bullet plodder afterall. Kep ya posted and see ya up the road.

Simon - like your description, am intrigued by your max points gap of 12 thou, I always supposed the gap should be 15 thou (2006 Classic 500 iron barrel)...am I out of date? How much difference does it make? Will 12 thou give me better tuning? I ask because I have recently had "issues" determining the maximum gap point of opening on my points, and the gap itself...

Cheers

TimG

Hi TimG, most makers advise a points gap between 12-15 thou, this is by no means critical and is only a guide, the setting will make no difference to the tune of the engine, in fact some people (on Magneto ignition mainly) use the points gap adjustment to fine tune the timing when you have no backplate to adjust. a certain school of thought indicates that increased compression requires the ignition to be retarded, however the difference is very small and in most cases can be ignored as long a pinking is not occurring, the ignition timing on all these older design engines is a bit hit and miss and varies with lots of different factors fuel quality air pressure humidity ETC, it is best set by ear done by someone with years of experience, failing that fall back on the makers norm.

Simon/Al . Do not understand your figure of 7/16 or 1/2". The piston should be at 0.8mm BTDC according to my information for static timing. Any old bit of wood or plastic will do, as long as you don't drop it, which a friend of mine did with the Bullet I sold him. All the messing to get the head off and the timing was spot on anyway. As a cheap and safe method , I would recommend an old coat hanger cut down, with a 90 degree bend about 2" from the end or buy one of Mr H's nice little tool made for the job and you cannot loose it down the hole.
Cheers Trevor.