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MG MGB GT V8 Factory Originals Technical - Pinking like a Maraca.

Gent's can anyone help please?
I have a 1970 Range Rover V8 in my MGB.
It has SD1 heads with 9.75:1 pistons.
I have just rebuilt it with new cam, rocker assy, rings, oil pump, Webber 500 carb, Dual Port manifold, Twin point Mallory, and Low Rider Filter.
It has a SS Block Hugger manifolds with a twin exhaust systen with balance pipe.
She ticks over a treat but under load sounds like there are a 1000 maraca's under the bonnet.
The timing is set to 3 BTDC.
Is this causing the problem, and would retarding the timing stop the noise?
The power is down and I am using quite a bit of oil but have no water loss.
Any help would be appreciated.
Regards
Dave
D M Tetlow

Dave

Firstly the timing marker could be inaccurate, they quite often are. I would check for true TDC on no.1 by taking out the plug and getting the piston to the top of it's stroke, then if necessary mark the pulley with a dot of bright paint and then re time the engine.

3BTDC is by no means over advanced 8-13 is not unusual depending on state of tune so it could be as simple as that. Rover V8's are pretty tolerant to inaccurate timing so if this does not sort the problem it may be worth having a look at the mechanical advance, broken or disconnected spring?

Something simpler do you have the vacuum hose connected to the correct port on the Weber? the correct port is the left hand one looking from the front of the car, if you have it on the other one it will give full vacuum advance from tickover.

Hope this helps,

Kevin.

Kevin Jackson

Thanks Kevin
I have the vacuum connected to the left port, and the distributor is brand new. It could be faulty of course.
I set TDC as carefully as I could so I hope it is indicating correctly.
I will try 13 BTDC to see what happens.
Regards
Dave
D M Tetlow

I wouldn't advance the ignition more without further investigation. If it's already pinking it may be overadvanced as it is and you need to find out whats causing the problem.

Kevin.
Kevin Jackson

Hi Dave,
Sounds too familiar. I had a 73 3.5 Rover engine that I installed 9.75 pistons (RPI)and had the same results. After reviewing the workshop manual, I found there are two types of pistons for different crankshafts in the early Rover engines. It states that they can not be interchanged. I purchased the wrong ones of course. I'm not sure why but I could not get mine to stop making a racket. I gave up after a few tries to make it better and purchased a later 4.0 engine.
All better now!

Kelly
Kelly Combes

Warm up the engine. Set the Idle to 2000. hook up a vacuum guage and turn the dist. until you get the highest vacuun reading. Retard the ignition until vacuun drops 1 to 2 in of mercury. Tighten the Dist.
See if that works.

Good luck
Steve
Steve

Thanks Steve.
I will give it a try.
Before I rebuilt the engine it ran OK. The pistons were as before the rebuild, I only had the crank reground and fitted new standard rings as there was no wear in the bores.
My gauge is in inches of water. Do you know the conversion from Mercury to water?
Regards
Dave
D M Tetlow

Dave,
The problem is that your timing curve doesn't match the needs of the engine. The Mallory dual point can be set to give a range of total mechanical advance and different weights and springs are available to give a steeper or shallower curve. Does it have a vacuum advance dashpot? It is possible to limit the travel of this dashpot to change total vacuum advance and several dashpots should be available, some of which have an allen adjustment through the vacuum spigot.

Your task is to adjust both the mechanical curve and the vacuum curve to match your engine. The mechanical curve should be set to match the engine's needs at WOT. The vacuum curve is set to advance the timing at part throttle for cruise economy.

Suck on the vacuum hose to make sure the mechanism is working properly and to see how much total vacuum advance it is giving you (engine running, timing light). You should have a plastic key which came with the distributor to set the limits for the mechanical advance. Initial timing around 10-15* is fine. I used to have a chart around here somewhere in which I had plotted the curves of a 215 distributor but I can't lay my havds on it at the moment. However, disconnect your vacuum advance and work on your mechanical first. Give it the max limit and road test. Write down the engine speed at which it first begins to ping under full load (WOT). Go back to the shop and connect the timing light. Bring the engine up to the same speed and read the timing. You now have the bottom of your timing curve. The rest gets trickier. You have to determine the the amount of advance the engine will tolerate well up into the powerband and usually somewhere around 2800-3500 rpm will work for this as mechanical advance is usually designed to be all in by this point. A dyno is probably the best tool for this because there is going to be a range where you get the best power and less advance is going to make less power but more advance is not necessarily going to result in any pinging noises that you can hear. And too much advance is going to destroy the engine. So probably the best advice is to work your way up the scale from your starting point. Plot a curve of RPM vs timing advance and locate that point and your initial timing, then read your timing light at different speeds, plot those points and see what your existing timing curve looks like. Then you can change weights and springs to make the curve steeper of shallower. I'm guessing you might need a shallower curve so stronger springs or lighter weights would help. You are trying to lower the curve at the point that pinging occurs but only at that point. Test, readjust, repeat. When you are able to get good power at any speed up to your mechanical advance limit you are ready to start on the vacuum timing.

Jim
Jim Blackwood

I would generally agree with Jim's direction but dyno time is expensive. The dizzy actually has two springs of various tensions. the first one is lighter and advances up "X" rpm. the second one is staged to slightly overlap the first and together both springs control the advance to the preset full advance. Sounds to me like your initial advance spring is to loose for the new engine and advancing the timing to early. Mallory make lots of different advance springs. It could be as easy as changing the initial spring tension.

All the best,

Mark.
M Mallaby

Thanks for your help Guys.
I shall try to access the curve needed.
Regards
Dave
P.S.
When fitting one of the new head gaskets I noticed that the pistons were not all orientated in the the same direction. Two of the pistons had the stamped on info 180deg to the other 2. Do you know if the pistons need to face front? May be this is the reason I am using a lot of oil!!
D M Tetlow

As far as I know the manual does not specify on piston direction but the rods are directional. They will fit the wrong way and will not be centered in the piston. There are arrows or boss on the big ends and they need to point towards each other on the journal. I've seen a few engines put together the wrong way (Rover and AH 3000) that ruined a crankshaft in short order.
Kelly Combes

Thanks Kelly.
As I was renewing the shells and the rings I did not think it was necessary to put the pistons back in the positions from where they were removed. All I did was to ensure the rods were fitted in the correct direction. I assume some rod/pistons from the left bank are now fitted on the right.
Regards
Dave
D M Tetlow

This thread was discussed between 19/09/2006 and 22/09/2006

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