Rev counter/ tachometer

[Dave Brand]

Originally posted by Revracing
That is not a problem! Lee spring manufacture torsion springs aswell..

Points don't use torsion springs!

Have you ever seen a set of points?

Originally posted by zefarelly
I have some 350lb strut springs but they wont fit inside the distributor cap

Just cut a hole in the cap & weld the other end of the spring to the inner wing!

I wondered about trashing an old set and using 2 springs together ?

Hmmm.....may be worth a try.You have nothing to lose.

[Revracing]

Yes I have seen a set of points!

However, not for some considerable time as I have been running electronic ignition systems and lately diesels.

I am only attempting to provide an additional source of springs which may or may not be of use to those in need, the manufactureer I mentioned will be more than happy to make a special one off to whatever spec is required (constant force?.

Dave you appear to be an experianced and knowledgeable person, I wonder why you seem to delight in demonstrating what from my point of view is a pendantic and not entirely beneficial area of your persona. Not everyone is anal retentive, not everyone veryfies there posts for technichal correctness, this is a discussion forum not a technical journal.

Ivan

[zefarelly]

several points well pointed out, but pointless bouncing abusive points at each other

[GTV27]

zefarelly, I have the exact same problem with my clubman - and it also has a smiths tacho (in fact, I wouldn't be surprised if it was orginally sourced from a cortina).

I had the tacho tested and it is fine, so the problem is in the ignition system somewhere - the thing is though, it runs electronic ignition, so I can't blame the points (and it may not be your problem either). I'm thinking about trying some diodes in the trigger to the tacho to filter out the unwanted spikes - any thoughts or comments from the collective wisdom of the forum would be greatfully accepted.

[alfasud]

I seem to remember something similar with my old alfasud sprint... could this be a symptom of misfire? It was a while back, but I seem to remember new plugs and/or clean the points made it go away.

Note, I didn't always replace the points, sometimes just cleaned... in which case it doesn't sound like points bounce... isn't that mainly a high RPM problem?

Sometimes, as GTV says, I think they might be a bit too sensitive to spikes.

[zefarelly]

Alfasud/GTV

I think its a spike of some sort, I have new plugs, coil, leads and points, the car runs fine (jst not powerful enough !!!) the rev counter is fine for about a minute after start up then starts going haywire, I'm a mechanical person and know little of electronics, so I'm stuck now. the only spikes I know about hold my tent down !

[Revracing]

This may have already been mentioned, but in the past I have had problems with a coil breaking down, all tested fine on bench (although I wasn't able to perform an insulation test) but after running for a while it would develop misfire problems and cut out at high revs.

Have you tried swapping components with new or or known quantities?

[1200Datto27]

Zef,

Have you tried different brand/temp spark plugs? it might sound strange, but the engine in my racecar only runs properly using heat range 9 NGK plugs, if I try others (even supposedly direct replacements), I lose power, have the rev limiter kick in at 4000 rpm, instead of 8500rpm, the tacho goes nuts, etc. It may just be the when the engine heats up (not sure if you use EFI or not) the temps/fueling are slightly off, and you are getting a very slight misfire that is feeding back through the tacho signal.

[Dave Brand]

Originally posted by zefarelly
I think its a spike of some sort, I have new plugs, coil, leads and points, the car runs fine (jst not powerful enough !!!) the rev counter is fine for about a minute after start up then starts going haywire,

Have you fitted a new capacitor (condenser)?

[zefarelly]

everythings new, including the rev counter, I'm going to try another rev counter next, we've just been on the roilling road and raced fine (aparet from an HT lead falling off !!!)

its old school, std ford Lucus points system, gold coil, NGK BPR7ES plugs and weber twin 40's precrossflow ford 1500

[1200Datto27]

Mines esentially the same engine, only made by Nissan (A15) however I run EFI and throttle bodies.

The engine makes about 100kw at the wheels, so it is not bad for that sort of engine.

I run AvGas (leaded 100 octane fuel) and a 13.1/1 comp ratio, so that may make a bit of difference.

It is possible that the HT lead has a loose connector (hence it falling off) and that is causing the false/missing signals to the tacho. It may even be the the vibrations from the engine running on track where causing it.

[zefarelly]

we've checked and sorted that little problem, and its still the same, until I check with another tacho I'm going to hold fire fiddling as its running fine, and I'm on my 2nd rev counter already !

[GTV27]

update: I've fitted a rev limiter with shift light ('cause my tacho bounces so much that it is effectively useless) and it is cutting in early and causing massive misfiring - which is apparently due to "interference" in the signal from the coil - which could be the same thing that is affecting the tacho (well it makes sense to me anyway).

It only occurs under load (ie it blips beautifully in the pits and for down changes, but won't pull worth a damn).

The diodes didn't help ( ) so I'm now going to try and physically shield the tacho and limiter signal wires (from each other and every thing else).

[big andy]

ive never seen a set of points bounce at 5500??????????

[zefarelly]

apparently its a spike on mine, no idea what to do about it . . . .encase the whole thin gin lead ??? :-)

I'm not convinced mine do at 5500 Andy, but when I was on the rolling road, with a snap on digital gun checking the revs once over 5000 it was reading all over the place . . . .engine sounded as sweet as a nut, but it cant be doing the top end performance any favours.

[1200Datto27]

Have you either tried closing down the gaps on the plugs (I run .6 mm), or trying either 1 heat range hotter and colder plugs. I don't know what plugs cost in the UK, but I play around $A10 for a set, and find that it is a cheap cure for most ignition related faults.

[zefarelly]

I was thinking about trying a cooler plug, but the car seems to run fine as is, and I can hear/feel where I am rev wise (years of riding 2 strokes that never had rev counters I guess) when I can be bothered I will change the counter again and possibly the points . . .. .what causes spikes is what I want to know !

[1200Datto27]

From what the guy that built my engine told me, if the pressure in the cylinder is high enough, the plug cannot discharge the full charge in time, leading it to bounce back through the ignition system, giving it a spike.

[1200Datto27]

Oh,

An engine will feel like it is running fine on different heat range plugs, but can make totally different torque/power curves.

[zefarelly]

ahh . . .now your talking, that makes some sense . . .Ive had similar on an old magneto system, I ran NGK BPR7's . . .when it got hot it conked out . . .cooled down . . .. fired up. when I went to 6's it was fine.

I may try 6's (standard) instead of 7's and see . . . .although I'm happy with the power output (for the engine spec at least) and dont want to risk loosing what I have got

[1200Datto27]

You might find that the 6's give you better power and drivability, give them a try. You might even try and find a set of 5's, and give them a quick try.

Have a look here for more info:
http://www.ngk.com/sparkplug411.asp

[zefarelly]

I had a set of snazzy 4 pronged posh plugs . . .the guy at the rolling road said theyre a waste of money . . on all the TVR race cars they look after they run std NGK's, at £8 a set you can afford to ditch them if theres any doubt!

[1200Datto27]

Yep,

Know the feeling, I bought some "You Beaut" Platnium plugs, and the damn things made no power, and had that much feedback from the restistance in them that the rev limiter kicked in at 2000 rpm, which is goo with a 1800 rpm idle speed.

[zefarelly]

ha ha . . ..a wide power band then