Timing and Balancing

[Malc]

Richard, You quoted retard as being about 50 degrees, was this the final figure settled on and is the "about" due to variations caused by temperature and voltage?I remember having various retard boxes for air cooled and from memory they would have the amount of retard written on which seemed to vary from about 42 to 50 and even one which was adjustable. none were any good as they were all more trouble than worth. I set one up to run by-passing the retard box but had to wait for confirmation from John Nelson who was service manager at the time before I could let it out for use.The riders response was that it was loads better, not having to have a second grasp at the throttle when pulling away from junctions. From then on all air cooled bikes had the retard by-passed.Then came along the Commanders which were not as bad until they smeared. As the police bikes were behind the privately sold Commanders and F1,s for Moly coating, it was a job to keep them on the road. As top speed was still reasonable and just tickover affected, the blue wire was disconnected to stop the retard kicking in as the engine got hot, and then the tickover was re-set.This was tried on a couple of bikes that had not smeared but the throttle response was not as good as on air cooled models so there was not such an advantage to be gained. Was there any reson for this?Malc

[Malc]

Second Question,Counter balance weights on Commanders have an extra piece of metal welded onto them. Why?I remember watching an air cooled shaft being balanced and the info keyed in was different between the air and water cooled models, again Why?I presume the higher compression ratio rotors are slightly heavier, does this have any effect? Is it to do with the flywheel weight difference between the 2 engines?The 2 engines (air cooled) I have with light flywheels on both had to have Commander counter balance weights fitted to get them to balance up, coincidence or necessity?One of these engines has has a lovely tick-over at 800rpm on full advance. This surprised me as the carb settings were transfered from a not so modified engine with a standard heavy flywheel (aux flywheel removed) which does not like to tick-over so much.Malc

[Richard Negus]

You quoted retard as being about 50 degrees, was this the final figure settled on and is the "about" due to variations caused by temperature and voltage?

Hi Malc,Both Sparkrite retard boxes and Boyer ignition units vary in their retard characteristics due to them being an assembly of discrete electronic components, each having slight variations in values and also having internal adjusters for fine tuing. Its fair to say that no two boxes perform exactly alike. Hence the label and Paddy Ryan's note either of actual retard or retard at the rev. limiter.In a similar way, no two engines are exactly the same; port finishing was done by hand and compression depends on the amount of leakage past the rotor seals.As the Norton rotary has so little dynamic friction, the amount of fuel/air at idle is very small and controlling by the throttle butterfly is not sufficiently accurate, hence the idle air bypass and adjusters. Even so, for a steady idle the ignition needs a huge amount of retard ; idling too fast generates heat and eventually leads to lubrication breakdown. The down-side of huge retard is the difficulty in getting the engine to accelerate immediately the throttle is opened.A bodge on the F1 was a microswitch on the carburettor to kid a hot engine, idling at full retard, that it was actually cold when the throttle was opened and put it at full advance immediately. It worked, providing the switch was adjusted correctly.I agree that Sparkrite retard boxes were more trouble than they're worth, in part due to the lack of weatherproofing. Disconnecting them resulted in a higher idle speed but, more importantly, as much better pick-up.Disconnecting the thermistor on a Commander gives the same result and can compensate for an engine with low compression.Digital boxes have the retard curve programmed into the chip and each one is the same as the next ; unfortunately, not all engines are the same so some variation in idle quality and throttle response from bike to bike is common. Have you looked under the lid of an RX8 to marvel at the electronics and plumbing there ? Spot the engine indeed ! All to get a driveable car and meet emissions regulations.Enough for the moment, I think ! R.

[Richard Negus]

Sorry Malc, second long answerCounter balance weights on Commanders have an extra piece of metal welded onto them. Why?'Cos the balance weight wasn't big enough, with no allowance for production variations !The rotating assembly should be dynamically balanced to a maximum 40 gram.mm at each end to obtain a smooth-running engine. As the shaft eccentricity is 11.6mm, this means that any variation in rotor weight has a significant effect on out-of-balance and the mass of balance weight required to correct it.The original design of balance weight, and the casing around it (primary cover) was done to suit a low compression rotor, possibly 7.5 : 1 ; higher compression rotors are heavier so need more mass at the balance weight to compensate. The casing fits so closely around the weight that any increase is only possible by the welded-on lumps at each end, as you've seen. A new, bigger, weight would have been better, but getting Jim-the-Welder to add a piece when needed was simpler/cheaper.The flywheel end doesn't have the same problem as there's so much more metal to play with in the balancing process.Note that the F1 has a much larger balance weight and doesn't suffer the same problem.I remember watching an air cooled shaft being balanced and the info keyed in was different between the air and water cooled models, again Why?As you suggest, different rotor and flywheel masses.The 2 engines (air cooled) I have with light flywheels on both had to have Commander counter balance weights fitted to get them to balance up, coincidence or necessity?Dynamic balancing the assembly is something of a black art, knowing that any change to one end has an effect on out-of-balance of the other end. It is an iterative process to get both ends within tolerance.One of these engines has has a lovely tick-over at 800rpm on full advance. This surprised me as the carb settings were transfered from a not so modified engine with a standard heavy flywheel (aux flywheel removed) which does not like to tick-over so much.It could be that it has more rotor seal leakage and more internal drag. This would not be significant once the throttle is opened as even a badly scored engine performs well (once you've actually got it running, that is).R.Coffee time already ? And a bun please.

[Malc]

Thanks for your detailed answers Richard, it is good to know the background information on these matters. There was quite a variation on the bikes I used to work on, although they were the same specification. As you know, this combined with the inconsistency of the problems encountered by the different forces that used them caused a bit of a 'headache' back at the factory.One other thing I meant to ask, many years ago, someone in the service dept (could have been Tony S or Brian D) told me that it was possible to change a rotor for a different one without re-balancing if they were near identical in weight. Would you know what a typical tolerance would be to do this?Malc

[Richard Negus]

I must admit that I've never done any practical tests myself to determine what is a maximum acceptable out-of-balance value before engine vibration becomes a problem to the rider (or to the main bearings).Aero engines used to be balanced to a wider tolerance as it was felt that vibration from the prop was far more significant than engine vibration.When Shenstone had its own balancer, a new rotor always meant re-balancing ; later, when balancing had to be sub-contracted, if I could find a rotor within 10 gms., I would use it without checking the balance. It didn't seem to give a noticeable increase in vibration so perhaps a wider balancing tolerance would be ok.I suppose it would be possible to take a heavier rotor, lighten it to the same weight as the one being replaced, whilst keeping it within its own dynamic balance limit.R.

[Malc]

Thanks again for that very useful info.,It might, after weighing, give an option of using a spare rotor that may be a better fit on a shaft. Malc

[Richard Negus]

an option of using a spare rotor that may be a better fit on a shaft. Malc

That's a whole new discussion !Shafts, and particularly air-cooled, tend to grow at the eccentrics during use and reduce the rotor bearing clearance below the accepted norm. The IP2 Manual, I think, used to recommend 30 - 35 microns diametral clearance but I favour more, particularly with a new (ish) shaft in an air-cooled engine.Mid West ran water-cooled aero engines at 45 - 55 microns without any adverse effects although I imagine it would be a bit noisy when cold in a silenced engine.With a shortage of shafts and cost of rotors, I have had rotors re-ground in the bore and used the -1/-3 bearing to get enough clearance.Shenstone used to have a Delapena honing machine but this sometimes produced a lobed, barrel-shaped bore in inexperienced hands. Grinding gives a better result but needs to make a bigger cut (circa 10 microns minimum).R.

[Malc]

The 'growing' of the shafts was something I found at an early stage of stripping air cooled engines. The factory's first line for sticking seals of filling with Red -Ex and allowing to soak very rarely worked, and if the about 1 in 6 chance it did work, the effects were only temporary, Usually by the next 6,000 mile service they had to be strpped and invariably the rotors were tight on the shafts.No problem, the factory would offer to delapane the rotors out to the correct size and supply the new bearings (and seal spring set) while I waited. So another day out while I waited for the rotors and shaft to acclimatize before being measured with the air guages, collect the parts and just home in time for tea! Good job the factory wasn't too far away.Malc

[Richard Negus]

My personal opinion of course, but I think that if synthetic oils such as Comp 2 had been specified for the IP2 from the beginning, then many of the engine problems would have been avoided. Failures due to seal sticking may have been reduced, but there would still have been the whole list of other things, some of which were eventually 'developed out' by the users.The first 'moly' plate that was done was an IP2 l/h which was actually sprayed bronze across the whole face. It went into a police IP2 but never heard of again (at least by me). I wonder where / how that one is now ?Subsequent ones were sprayed with cast iron or stainless steel, until molybdenum was chosen as the preferred metal. They're all out there somewhere.I know all the faults with the IP2, but was the BMW R80 really any better for the job? R.

[Interpol2471]

I know all the faults with the IP2, but was the BMW R80 really any better for the job? R.

I bought a set of IP2 discs of an ex Police rider some time ago and he said to me that the IP2 was the best bike in his oppinion that the Police ever used. His only complaint was the slow running issue on convoy / escort duties and getting hot but other than that he said it made the best flames from the exhaust of any bike he had ever ridden ( I must try that some day )

[Richard Negus]

[quote he said it made the best flames from the exhaust of any bike he had ever ridden ( I must try that some day ) [/quote]30 - 40mph in 5th, operate the kill switch for a few seconds keeping the throttle open, filling the exhaust with unburned fuel, switch on again and ......BANG !R.ps, Paul - one step forward, two steps back.

[Interpol2471]

Ypu shouldn't tell me things like that

[Richard Negus]

Ypu shouldn't tell me things like that

It was actually one of the recognised ways of determining whether an IP2 engine was suffering pre-ignition when used very hard.Firstly, the engine starts to sound harsh, the temperature gauge rises rapidly - and then it doesn't stop when switched off.Carbon deposits on the rotor become incandescent, enough to provide the ignition, and if the throttle is not closed, lead to unscheduled cremation.I've seen quite a lot of police IP2's for repair under warranty where carbon on the rotor flanks has been white/beige, a sign that pre-ignition may have been occuringI don't recall it ever happening with a water-cooled engine, but then they don't run anywhere near as hot.Bob Rowley (Chief Tester, amongst other functions) says he could always induce an IP2 to pre-ignition - but then he could scrape centre stands on wet roundabouts too ! R.PR - YM !

[Malc]

The R80's were definately no better and the only reason Derbyshire changed wholly to Nortons was because they were cheaper to run.The problem was/is that police bikes are abused and thrashed to their limits (and beyond) so it was only when the K100 became available for police use that problems declined, only to increase again with the K1100. (The first K100 were unable to be used as police bikes because when the transmit button on the radio was pressed, it cut out the early jetronic ECU)The R80,s were thrashed hard from cold by some riders and with a top speed of only 105 mph, they were often flat out everywhere exept in towns.Picked one R80 up from Scotch Corner after the rider reported the engine felt tight but it had done approx 90 miles up the M1/A1 on constant full throttle, making good progress as they used to say. This was a nikasil coated bore model so only needed a clean up and new rings and valves and guides. It was common for them to drop valves and wreck pistons. Oil consumption could be almost as high as the total loss system on the Nortons and then were the other problems; Silencers would often need relacing at 2 or 3 year intervals ( never replaced a Norton one), centre stands would break and valve clearances would tighten up by every service. The engines would become so noisy that BMW would supply 'quietning kits', nylon washers for between the rocker posts and rubber inserts for between the fins. A privately owned R80 would be quieter at 50,000 miles than a police one with 20,000 miles. There were also handling problems and rear tyrs had to be changed at 3 mm where as Nortons Pirellis could be changed at 2 mm. Michelin, who also had the contract for car tyres then came up with a tyre that could also be run down to 2mm on the R80 but I cant remember if BMW approved this.Gearboxes did last longer than Norton ones but thats another story!The Nortons certainly made life intersting and I was never short of work, which was a good thing as I was specifically emplyed as a motorcycle mechanic but when things were slack I had to help out on cars, vans or generatorsand while we had Nortons, things were never slack!The Nortons were also abused and revving the engine and flicking the kill switch on and off seemed to be a party trick for some riders. I remember firearms squad being called out because there had been reports of the sound of gun being fired but theonly thing found in the area was a Norton rider.The air cooled driving school bikes did not suffer from sticking seals anything like as much as the bikes used in the cities. All Derbyshire bikes were changed to Silkoline Comp2 simply because Silkoline got the contract to supply all oils for the fleet of vehicles. Comp2 was the only oil Silkoline would recommend even though at this time the oil had not been tested or approved by the factory.Malc

[Malc]

As I have mentioned before, another reason for 'cooked' air cooled bikes was the single battery which could never cope with the demands on it. Riders at an incident requiring lights to be used would wedge the twistgrip open with a lolipop stick to keep the engine at a very fast tickover to keep the lights powered.Malc

[Richard Negus]

Hi Malc,Did you notice any reduction in seal sticking or end plate scoring when Comp 2 was introduced ? The simple smoke test for oils at Shenstone showed that it vaporised at a higher temperature than Rotella and left less of a residue.Mid-West did the same sort of tests and intially only approved Comp 2 for the aero engines. When 99% of their single rotor production (some 400 engines) went to Schleicher in Germany, there were problems for the eventual aircraft owner to get the oil. Later, Bardahl KGR (another expensive synthetic) was approved ; blended in Italy and more generally available - but not in this country.Unburned KGR is even more 'sticky' than Comp 2 and probably better protect the internals of an infrequently-used engine.On the subject of generator / battery capacity, the design brief of the Commander included a doubling of both from the IP2 spec. The generator turned out not to be quite double, but was the biggest permanent-magnet one available at that time. On my own Commander, I've almost tripled the output by having a belt-driven car type alternator of 50A. As a standard automotive part, it includes the regulator and has the facility of a warning light to tell when it's stopped working (= broken belt).My Egli Laverda endurance racer had a similar set-up in 1975 ; the riders had the best lights on the track and no problem with electric starting either.R