Continually retarding...

1396midget

1396midget

Well-Known Member
Hi All

Every 1000 miles or so I need to re-fettle the V8, as it suffers from audible part throttle pinking. I retard it by turning the distributor and testing till the pinking has gone, 1000 miles later it's back and I have to do it all over again. Distributor clamp is done up as tight as seems sensible with an alloy thread. It's a Mallory twin-point distributor, and was fitted at the same time as the engine (according to receipts).

Any Ideas? Is it the twin point being silly?

Thanks 8)
 
i hope not... but i had that happen once upon a time and it was the timing chain... ?

Rich
 
I'm not familiar with the V8 engine, but.......
Is the pinchbolt gripping properly?
I had this problem with a pinchbolt on the throttle balance shaft of my old carb setup. It kept slipping, so I did the bolt up as tight as it would go, but what I didn't realise was that I simply distorting the bolt-retaining hoops, turning the 'pinch' bit into an oval shape that no longer gripped the shaft properly. Grab the dizzy body (ooo, er, missus! :wink: ) and see if it will budge by hand with a good bit of force....

Could be something else entirely, of course! That was just my experience of a pinch-bolt. I'm now conscious to only tighten them up just enough to grip fully, and never go for the 'one-for-luck' extra half turn. I also always put them back to the same tension if I remove them and never slacken them as they may be distorted!

Michael
 
Boo I hope it isn't a timing chain issue. Engine is not that old (around 20K miles), but you never know. Any way of checking that?

I'd come across that issue on the A series Michael, the V8 is a bit different though as it has a sort of claw that pushes the distributor down towards the drive gear to lock it. Though maybe this is slipping around too.
 
Not sure how you check but I know the timing gear is nylon and they aren't the best specced thing in the world..
 
If the chain is stretching or the teeth worn then your valve timing would be retarded too. You could probably check this with the plugs out, valve covers off and the fuel pump out to see the chain.
 
1396midget said:
I'd come across that issue on the A series Michael, the V8 is a bit different though as it has a sort of claw that pushes the distributor down towards the drive gear to lock it. Though maybe this is slipping around too.
Click to expand...

Ahhh, I see. Sorry, I don't know much about that engine. My approach to most issues is always to be methodical, and look at the simple variables first. At least that way you can be sure all the little things all work.... and it helps you to slowly (and at your own pace) face up to the fact that something major might need doing!!

Hope you get it sorted!
Michael
 
1396midget wrote,...
Hi All

Every 1000 miles or so I need to re-fettle the V8, as it suffers from audible part throttle pinking. I retard it by turning the distributor and testing till the pinking has gone, 1000 miles later it's back and I have to do it all over again. Distributor clamp is done up as tight as seems sensible with an alloy thread. It's a Mallory twin-point distributor, and was fitted at the same time as the engine (according to receipts).

Any Ideas? Is it the twin point being silly?
Click to expand...

Hi 1396m,

You can check the timing chain by using a timing light. As you increase the revs whilst watching the timing marks, do they wander slightly back and forth? If so then the timing set is worn in some way, chain loose etc. With a good quality timing set as you perform this test, there should be no wandering at all.

I have no experience with Mallory distributors, but I have heard that some owners have good success whilst others have nothing but problems when using them. Ignition timing from memory will always need adjustment when running points, a very good reason to remove and fit an electronic ignition system.

Ron.
 
i had this problem with mth about 2 years ago and found out it was the dizzy it self so much wear in it so replaced it with a spare 1 i had then had no problems
 
Cheers fellas, some things to try then.

The dissy is also not that old, mileage wise, but is over 10 years in time. I'll check it over with dad's strobe over Christmas, and see if it's being odd. I'll be checking that the timing mark on the pulley is in the right place first though, after a bad experience with the Midget!

Thanks

Rob
 
Presumably you know what you are setting it too? :?

If not and you're just doing it by ear at least mark the dizzy to tell if it's moving on you :wink:

If the points are closing then you will be able to measure the gap or the dwell meter will show you. I'd check here first TBH as this effects the timing anyway and may save you messing with the other stuff you mentioned :)
 
'factory' is 6 degrees BTDC isn''t it, for 100 Octane petrol. Though people seem to set anywhere between this and TDC (seems to be very engine dependent)

Points Gap I can do, the dwell is a bit odd in the twin point as far as I can see, there's a set for starting and a set for ending so presumably the dwell is set between the two sets of points rather than in the normal way.

Can't find anything useful on setting up the Mallory's, though there is a massive chunk of info in the original WS manual :)

Cheers :)
 
Well, the Mallory twin point is meant to be the DB's for the Rover V8 (in fact all V8's), so I'm reluctant to blame the distributor.

I think i might start back at the beginning and try and remember whether there is anything you are doing that might affect fuel quality - using two different filling stations perhaps? Also don't forget that fuel mixture also affects pinking - setting a tad rich always helps. So make sure the carbs aren't drifting - perhaps you have a sticky choke action that sometimes returns the jet fully and sometimes not? Is the cooling system 100%, particularely, have you got all the air out of the top of the engine via the carb tower, so that you don't get any localised hot spots triggering the pinking?

Then we're back to the timing. First verify that the timing really is moving and it's not just you being hypercritical in response to the pinking. Then an exploration of backlash and looseness issues in the timing chain/distributor drive/distributor. Slop sideways in the dissy shaft (worn bearings), slop rotationally at the dissy (worn timing chain/gears). Then do you have fresh points in - Rimmers sell them at least. What about capacitor? A dodgy one might well cause the points to wear over rapidly?

As a hint, you can take the load off a twin point to stop the points wearing by fitting an ignition amplifier. This converts the points into a low currect trigger for the amp, which does the hard work of switching the inductive load of the coil. That way you get the benefit of stable timing and nil maintenance without having to throw away your distributor. I've used the RPi set up which is nice and large and bomb proof, but I'm sure there must be others.

Chris
 
Hi Chris, thanks for the reply :)

chrisyork said:
Well, the Mallory twin point is meant to be the DB's for the Rover V8
Click to expand...

That's what I thought as well, some sources on the net also reckon it drifts its dwell angle, but then you tend to only get reports from the bad ones and I'm not totally ready to believe it is just the dissy.

chrisyork said:
using two different filling stations
Click to expand...

certainly been doing that, but it seems to change over a larger amount of time than just a tank, I go about 200 miles on one tank (to be safe as fuel gauge is not working at the mo) and it pinks on some tanks and not on others, and starts during the same tank full. This'll be the third time I've had to adjust it since I got it, and I've done about 4000 miles in it so far. If I can't find anything else that's odd then I'll stick to one station.

chrisyork said:
fuel mixture also affects pinking
Click to expand...

Yep, Dad's got a colourtune so going to give that a go as well. I know it's running ever so slightly on the lean side by the plug colour, but as it doesn't pink all the time...

chrisyork said:
the carbs
Click to expand...

had the choke stuff all apart as it did stick on previously, but it's in line for a full carb rebuild as part of it's christmas present.

chrisyork said:
Is the cooling system 100%,
Click to expand...

as far as I know, yes, 2K miles ago I had it all apart and flushed it out to make the heater work better. Will check it again though, especially that little thing in the top of the carb tower that plugs up as soon as you look at it.

chrisyork said:
timing
Click to expand...

Thanks, will check all those bits.

chrisyork said:
Ignition amplifier
Click to expand...

Hadn't thought of that, will have a look at them. I don't want to treat a symptom rather than a cure though, so maybe that's a last resort if the points are being silly.

thanks :) :)
 
Interesting snag, this.
If you are having to constantly turn the dizzy the same way to reset it, my money is on the timing gears/chain or both.
I would remove the inlet manifold and valley pan gasket and with the plugs out, turn the engine in the normal direction of rotation until the timing marks come up on the pointer then when it reaches the end of the scale on the pulley, turn the engine back until the cam starts to turn again then stop (You can see the cam in the valley with it opened up). You will have a representation on the timing marks and the pointer to gauge the amount of slack in the timing geartrain that way.

The degrees turned on the pulley before the cam starts to turn should not be very much, I'd guess around 2-4 degrees, maximum. Any more than that and I would say you need to replace the timing gear.
If you have a cam gear handy by, count the number of teeth and calculate the number of degrees lost if it skips a tooth, and use that as a guide to how far you are able to let it slide before it becomes a worry. From a photo of the RV8 timing gear on a website, (http://www.rimmerbros.co.uk/Item--i-GRID010806) I count 42 teeth and that gives roughly 8.5 degrees per tooth, so if you are having geartrain problems, then you could well be approaching the point where tooth wear and chain stretch reach the point where it skips a tooth, leaving you with far more than wandering ignition timing to worry about.

Not trying to scaremonger you, but think about it.....
 
This is what eventually happens to the OEM nylon toothed timing gear as fitted to all P6B engines.

F1000008.jpg


Only two teeth remain intact, all the rest have broken off... :shock: Mind you this was after 203,000 Miles (327,000km). Surprisingly, the engine was still running smoothly and with great luck the chain had not slipped so valves had yet to make contact with a piston or two. Would have been just a matter of time though.....

Ron.
 
If it looks like the chain/cog are giving up the ghost then if you intend to do any engine upgrades - cam etc then i guess this could be the time too...?

Rich
 
I wonder if RPI put a new timing gear set in when they rebuilt the engine or if they re-used the old ones...

I'll do all the checks first to make sure it's not the gears, then if it is, out with the spanners (and the wallet) and on with the thinking cap.

In an idle moment today I came across some really good threads on top end rebuilds, I've got some big valve heads coming (a tenner from eBay) and was planning on doing them at some point, so as said, perhaps now is the time. If it turns out to be the timing gear. *sneaks off to look at cams*

At least I have some other cars to play with while it's in bits, if it comes to that.

Thanks guys, I'll keep you updated on any progress made next week :)
 
Success!

timing was set to about 10 degrees BTDC, and there was no wavering whatsoever on the mark, so assuming timing chain stuff is OK :)

So set it to 6, and spotted that the distributor clamp had been digging a hole in the mallory alloy clamp area, making a little slot at 10 degrees, which presumably over time the dizzy will rotate as the clamp 'falls' into the slots.

So I've bent the clamp a bit differently, tidied up the mallory clamp area, and put little cross hatchings into the grippy ends of the clamp. Tightened it up, popped a spring washer on it as well so there's no need for it to be as tight as a badgers whatsit any more, and hey presto there's some stable timing. Done 500 miles in it since and it's still on 6, with no pinking at all.

It now goes like stink as well cos I cut off the rear silencer and replaced it with a straight pipe. Which I then made dad weld another one on so now it has 2 and sounds like the end of the world is happening! :D :D :D :D :D :D :D what a noise! But nice and restrained inside still. And fixed the fuel gauge.

Took a plug out and its a long reach one I think, so i'll be measuring the head threads tomorrow to see if I have SD1 heads, then it's off to get some new plugs to see if I can track down a high speed misfire that's been getting worse for about 3 weeks...

thanks for all your help guys :)
 
You must log in or register to reply here.
Back
Top