timing/pre-ignition

[norseman]

Got an iritating problem with my '87 3.5efi Classic. Despite setting the timing as per the LR w/shop manual the car persists in 'pinking' when the revs climb above around 3000 when accelerating hard (ie during overtaking or during a hill climb). The car has only covered 47k & with only 2 previous owners (one company & one old boy) is unlikely to have been messed with. The manual has various data for the timing (9.35:1) according to the model year & interestingly different requirements for the fuel octane(!) According to the data mine will run on 94 but I've tried a couple of tanks of 97 as well. Am I right in assuming that the dissy has to be removed to check the ser. # is correct for the model year?

 

[wammers]

Ok tried to answer but misread engine size. But. Cannot find in my manuals any tuning data for a 3.5 with 9.35 to1 compression ratio only for 8.13 to 1. Only for 3.9 has 9.35 ratio according to my data. However dynamic timing, Vac disconnected engine at tickover is 5 degrees BTDC on HC 3.9 and 6 degrees BTDC on lower compression 3.5. Checked with a strobe lamp. Have you got the correct plugs in they can cause pinking if they are not the right grade and glow causing pre ingnition.

 

[norseman]

Thanks Wammers but I do have the genuine LR manual. My query is that although I've followed the 'good book' the engine still pinks. As to your suggestion of plug choice the book lists N9YC fpr both '86 & '87 model years but changes to RN12YC for the '88 but I think that these are the only spec. now available & I think that's what is in mine. The timing setting for '88 changed to 6degrees BTDC & 95 octane as opposed to TDC & 94 octane for my '87, seems a big mood swing on LR's part! I'm assuming that the variation in dizzy serials nos. denotes different advance curves, hence the need to check mine.

 

[landowner]

Thanks Wammers but I do have the genuine LR manual. My query is that although I've followed the 'good book' the engine still pinks. As to your suggestion of plug choice the book lists N9YC fpr both '86 & '87 model years but changes to RN12YC for the '88 but I think that these are the only spec. now available & I think that's what is in mine. The timing setting for '88 changed to 6degrees BTDC & 95 octane as opposed to TDC & 94 octane for my '87, seems a big mood swing on LR's part! I'm assuming that the variation in dizzy serials nos. denotes different advance curves, hence the need to check mine.

If it pinks its over advanced no matter what the manual says.

Just retard it back a little till the pinking stops.

Manuals dont allow for wear in the parts and so are only a guide, I just advance until it pinks under load and then drop it back till the pinking stops and that is the best you will achieve for the engine without a rolling road.

 

[wammers]

Thanks Wammers but I do have the genuine LR manual. My query is that although I've followed the 'good book' the engine still pinks. As to your suggestion of plug choice the book lists N9YC fpr both '86 & '87 model years but changes to RN12YC for the '88 but I think that these are the only spec. now available & I think that's what is in mine. The timing setting for '88 changed to 6degrees BTDC & 95 octane as opposed to TDC & 94 octane for my '87, seems a big mood swing on LR's part! I'm assuming that the variation in dizzy serials nos. denotes different advance curves, hence the need to check mine.

For that model i only have NAS manuals. There are differences in model year specs and introduction Etc. Maybe the 3.5 HC engine was not exported to the states. Seems strange that the HC engine has less dynamic advance than the LC engine. So maybe you are right about the dizzy. Maybe it has stronger springs or different bob weights to change the advance curve. But plugs can make a difference, harder grades are less liable to cause pinking than softer ones on HC engines.

 

[wammers]

If it pinks its over advanced no matter what the manual says.

Just retard it back a little till the pinking stops.

Manuals dont allow for wear in the parts and so are only a guide, I just advance until it pinks under load and then drop it back till the pinking stops and that is the best you will achieve for the engine without a rolling road.

Only if the distributor is functioning properly. 5 or 6 degrees dynamic is not a lot for an HC engine, you would expect 6 to 8 at least and upto 12 on some. At 3000 rpm the advance will be 30 degrees or more. So knocking back the dynamic will not change that at all if the dizzy springs have gone weak. It is just adjusting out the problem instead of correcting it, by having a properly functioning distributor. You may indeed have a situation were backing off the advance at 3000 rpm under load to stop pinking may in fact have your static set retarded. And you really do not want that.

 

[Datatek]

If it pinks its over advanced no matter what the manual says.

Just retard it back a little till the pinking stops.

Manuals dont allow for wear in the parts and so are only a guide, I just advance until it pinks under load and then drop it back till the pinking stops and that is the best you will achieve for the engine without a rolling road.

I like your signature pic is that an opposed piston Commer 2 stroke diesel lump or the one that appeared in some Fodens? They were incredibly noisy.

 

[wammers]

I like your signature pic is that an opposed piston Commer 2 stroke diesel lump or the one that appeared in some Fodens? They were incredibly noisy.

It's a supercharged Commer TS3 Keith, dirtiest bloody engine to work on in history. But what a good lump they were.

 

[norseman]

Thanks for the replies so far everyone. To return to my original question, does the dizzy need to come out to read the ser #? I've used the 'road test' method in the past (I'm that age group!) but clear results are not as easy with an autobox.

 

[wammers]

Thanks for the replies so far everyone. To return to my original question, does the dizzy need to come out to read the ser #? I've used the 'road test' method in the past (I'm that age group!) but clear results are not as easy with an autobox.

Only if you can't see the serial plate with a mirror/torch or some other method. Whip the top off and see if the springs have worn the bob weights so they are loose. Or a spring has broken. If the bob weights are rattling about. That could also be your problem.

 

[Datatek]

It's a supercharged Commer TS3 Keith, dirtiest bloody engine to work on in history. But what a good lump they were.

I thought so Tony, although I did not know the type designation. All I really remember is the noise when the dustcart blew a silencer

 

[Diesel Do]

A very helpful chap at RPI told me never to believe the timing marks on them, he advised find a long hill adjust it till it pinks then back it off so it doesn't and that's as good as you'll get on them?!?! Obviously you need a dizzy that's ok too! But that method worked pretty well for me

 

[landowner]

Whip the top off and see if the springs have worn the bob weights so they are loose. Or a spring has broken. If the bob weights are rattling about. That could also be your problem.

As above
The springs sometimes wear a groove in the locating pegs and become loose. You can bend them to take up the slack if that has happened but be careful because one of them is supposed to be a little slacker than the other.
Alternative is to sleeve the pegs with a little tubing to take out the wear.

You can bend unworn pegs on the stiffer spring to hold back the advance if its the wrong spec dizzy.

As long as you dont retard too much because engines like as much advance as you can give them without pinking.

 

[norseman]

Thanks for all the replies folks, I'll get the dizzy checked out in time. Would'nt have thought there would be that much wear at 47k (40k when I first bought the car & noticed the occassional 'ping') but who knows?