Speed Ceiling

[Guest salty_monk]

 

How does sod off sound!!!

 

Seriously though - really want to get this one nailed... it's doing my head in! If it wasn't such a pig of a job (relatively) I'd put the old diff back in again to make sure... maybe not such a bad idea - I'll get it reconditioned (again!) first...

[Longboarder]

Seriously for a moment, once you are sure that the recent change of diff has not directly caused the problem then you should be back to basics without any preconceived diagnosis.

It's check through the ignition from scratch. i.e. pos supply to coil, neg to dizzy, coil itself (fit a spare), magnecor unit (refit points?), rotor arm, cap, HT leads, plugs and timing (use electrical test meter to check coil, HT leads and volts at the coil pos supply). Then same detail through the fueling. Finish off with mechanicals like compression, cam timing and tappets.

 

Nigel

[Guest salty_monk]

Hi Nigel,

 

Am a little ahead of you on this one as:

 

Had points + condensor & Intermotor coil - Changed for Ignitor kit (magnetronic ignition) & Matched coil.

 

Changed Rotor arm for "Rev limiting model" that I had in the shed (cuts in a bit early actually not the advertised 6,700)

 

Timing was adjusted on the rolling road & cap looks to be in good condition as do leads & plugs.

 

Problem is still there...

 

For what it will cost me I may change the fuel pump, filter, plugs (go for a harder 7 plug rather than the 6 I am currently using), cap & leads in turn to see if it makes any difference - still don't understand why it doesn't affect all gears though - that's the real head ****!

 

Can you give me some hints on what I need to check for on the leads, & + at the coil?? I have a meter so I could give that a go tomorrow...

 

Engine doesn't smoke - ever & never uses any oil so I'm guessing that the rings & seals & thus compression are all pretty good - as for tappets is there some adjustment I can make that would only affect it in high gear? It does sound a little "tappety". (Didn't know you could adjust the tappets on the pinto presumed they were just rockers & followers) I have the Piper 285 cam fitted but no vernier pulley, the RR should have picked up if it was a tooth out though surely??

[Guest Battery Bill]

Dan

Didn't know you could adjust the tappets on the pinto presumed they were just rockers & followers

Well instead of adjusting your tappets adjust your rockers

Can't see why they would cause the top gear problem though, I think it must be the diff

[Guest salty_monk]

Certainly everything seems to point to it - the only other thing I did at about the same time was rewire the fan so that it is activated through a sender - now that I really can't see having an effect!

 

Am making enquiries to having the old diff reconditioned so I can put it back in & see what difference it makes.

 

My trip to China is now postponed so there is now every chance I might make Barkston Heath - I should know by Tuesday so if the answer is yes I hope there's still a place for me... - perhaps we can have a full pit analysis on it after the event!! (certainly be a few more peops whose ears I can tug anyway!! :lol:)

 

Cheers,

 

Dan

[Grim]

maybe the oil in your diff is more viscous

[Guest Battery Bill]

Dan

the only other thing I did at about the same time was rewire the fan so that it is activated through a sender

Perhaps you have wired it wrong and when you get into top gear it runs in reverse thus pushing air forward and slowing your forward motion

See you at Barkston Hopefully

[Guest salty_monk]

at least I can say that the fan is one thing working properly! (After I got over the problem where the final wire from Relay to Fan motor spuriously developed a 7 volt voltage drop from nowhere, just blanked it off & ran a new wire) - is it me or is this car bloody troublesome?? maybe I should Ebay it & get another one! :lol:

 

Better the devil you know as they say

[Peter Bell]

Try going back to the original rotor arm instead of the spring loaded one.

Peter

[Guest salty_monk]

Hi Peter,

 

I'll try that tomorrow but it was doing this before I fitted the spring loaded one with a standard (1,600 mile) old one....

 

Dan

[Longboarder]

Peter's on a similar wavelength to me. If you can Identify drop in performance after making changes try going back to the previous configuration and see if that helps.I would usualy take this approach as opposed to accepting a random unexpected failure or problem because its quicker to check the things you have just changed than do a complete methodical diagnostic. Think back to when you first noticed the speed ceiling and try to think of the configuration of the car at that time. Was it before you fitted the magnecor unit and coil or after. What order did you do the various changes. When did the fault appear relative to which change, etc. When was the car last at 110 mph. How long ago was that. What bits were on it then that have since been changed. Was it deteriorating before you started changing bits and that was why you upgraded.

Don't assume that because you fitted a new magnecor and coil that one of them has not become faulty. Difficult to check the magnecor so refit the old points and coil (not an electronic coil which will destroy the points).

Check you have 12 volts at the pos lead on the coil (To eliminate faulty ignition relay or ignition switch, connector or wire in circuit). HT leads depending on type should have a resistance of about 2-3 ohms per foot.

 

Nigel

[Guest Friar Tuck]

I seem to recall an earlier thread where it was discussing the venting of gearboxes, diffs etc.

 

Have you checked that the replacement diff is not overfilled, and does it have a breather ?

 

I may be miles off, but reading your thread it sounds possible, in theory anyway that this could actually be holding you back, and you are currently looking at the wrong end of the car ???

 

Good luck, whatever the problem turns out to be, it is surely a process of elimination.

 

Cheers

 

The Friar

[Guest salty_monk]

Friar - Certainly seems to be! Will be working on it today... The thought that the diff could be too full crossed my mind too (breather is ok) I used EP90 but unless Comma are telling fibs about container quantities the diff actually took just over 1ltr to come up to the right level (haynes states 0.9ltr). Can't really see that having this much of an effect but I will check the level again & perhaps take some oil out today...

 

Nigel - The problem started when I had made only 2 changes:

 

1. the diff

2. the fan & sender unit (from a switched unit, re-wired & rejigged the relay).

 

As far as I can recall there was no "speed ceiling" before these changes.

 

Looking at that statement all I can say is that it can only be the diff, the voltage to the coil (perhaps I disturbed something when I rewired the fan) or deterioration of something (perhaps plugs or leads) due to heat (but a dodgy plug or lead should show up in all gears & produce a misfire or something surely!).

 

All other changes were upgrades I already had planned & were not done specifically to overcome the problem (although I had put the speed ceiling down to badly closed up points in the first instance). The problem has remained through the replacement of the ignition components & the RR tune - I think Friar may be right, perhaps I should be looking at Diff or box. Will certainly get quotes to re-con old diff to think about putting that back in...

[Guest salty_monk]

Ok - been testing today. All the playing with fuel has made no difference.

It cannot be fuel starvation as if I:

 

1. Hold it at 4k or so on the drive the filter does not empty out

2. Hold it at 5k in 3rd gear power does not drop off.

 

This & the power curve from the rolling road (2 days ago) has convinced me it is not electric or fuel...

 

So - back to the diff then - everything points here, be interesting to hear what Big Jim has to say when he re-surfaces perhaps he can shed some light.

 

What do you think - do I put the old diff back in as it is as a pure "test" or do I get it re-conditioned first & then try it??

 

I can't believe it is just coincidence!

[Big Jim]

It's not the diff! a diff will either work or scream abuse if it doesn't want to!

It's somewhere on your engine set up. Now you know my feelings on points!

you've got a cocked up set up there, I would suggest that your timing isn't correct (& I don't care what your RR man say's!)

 

Get a proper timing light, check out Dave Andrew's web site about ignition timing, and set it up to that. Ie. you work backwards, you set it up at "full advance" which should be there at 3500rpm (if your dizzy is correct) no later, then check that it's no more than 20ºBTDC at idle (1000rpm with a lumpy cam)