Big Healey Timing

- snipped all the bits I don't know anything about -

I wonder if this may be the clue. I don't know much about that particular engine, but on the XK which has some similarities - straight six, two or three SU carbs depending on model, quite a choice of cams - you should never just change the cam(s) alone. It is essential to modify the advance curve to suit, and normally re-jet the carbs. A later (hotter?) cam alone just won't work.

Big Healeys are very popular in classic rallying, so I'm sure there must be engine tuners out there specialising in the models. Probably best to start with the owners' club - there must be one - and look for recommendations. Preferably someone with access to a rolling road and a good history of building successful competition engines. I know it will cost, but it seems to me you've already done all that could be expected from a home enthusiast. You'll probably get the money back in reduced fuel consumption, and certainly in driving pleasure!

Sorry I can't be more help.

Geoff MacK

The message from "Geoff Mackenzie" contains these words:

It is a long time since I had a Big Healey (100/4 in my case) but the early cars were only 2660cc while the BJ8 was the last in the 3000 (2912cc) series. (Memory refreshed on Internet). I would be at all surprised if the later cam required all the modifications above to work properly.

You are both right, the early 6 cyl cars were 2.6, the later ones of 2.9 had the same stroke, with a bigger bore, mine is a 2.6 bored out to 2.7. I have run it with a "works" rally cam but it was too lumpy for road use; I have changed the distributor for a modern one to go with the last of the "fast road" cam so they should match. The carbs are the triple SU set from an MGC proffessionally fitted by John Chatham in Bristol, and plug and exhaust colours are correct. It was OK to begin with, it has gradually got worse over the years. It has been mainly used on the Monte Carlo Challenge, quite succesfully, but each year it runs hotter and hotter. one year I added an oil cooler, one year I changed the Rad for one with a bigger core, now it overheats just idling! I'm going to reassemble it now as it was, I'm thinking that it must be the rocker clearance, as it is the only thing that I can think of that can change itself over time. But I still don't think tight tappets will cause overheating at idle.

The only two tuning causes for overheating I can think of are retarded ignition and/or weak mixture. But overheating at idle would suggest a problem with coolant flow. Is the waterpump ok? Has the system been used with plain water so the water jacket is badly corroded and partially blocked?

FWIW, I reckon unleaded (even 97/8 octane) requires very different static and dynamic ignition timing from the old leaded for best results. And that's before you start altering valve timing with a different camshaft.

I'd say a session on a rolling road is needed. Not that I can suggest where - perhaps others could.

AFAIK the only downside of tight tappets is that you will burn out the valves in due course. The fact that the overheating problem is becoming progressively worse makes me think that the problem could be general sludge in the waterways. It's surprisingly difficult to get all the crap out - for example, my XK engine was rebuilt from bare block in about 1999; a completely unrelated problem necessitated another rebuild in 2005 and the engine man was amazed by the sheer quantity of sludge he blew out. I don't know how difficult this would be on your car - for example, you would need to take all the core plugs out - can you do this with the engine in place? I reckon this would be a good starting point - get the internals completely and utterly clean. Tempted to say "operating theatre" standard, but maybe Big Healeys are succeptible to MRSA so aim for something better!

Good luck, and keep us informed.

Geoff MacK

Were you using a decent quality 'aluminium' antifreeze all year round - or just plain water?

I'd like to say it has always had antifreeze in it, but I know there have been occasions when it hasn't, like when it has had work done and I fill it up with plain water to test it, then fill with antifreeze later - sometimes months later when I remember. As it has an aluminium head, I am aware of the corrossion problem so I'm usually quite quick on it, but not always. I will try to reassemble it this weekend and do a few tests. To me the most strange thing is it needing to be so far advanced to run smoothly; I'd have thought any engine with more than 10 degrees of advance during cranking would try to run backwards ( remembering my Bikes with kickstarts) Yet it starts fine with nearly 30 degrees advance. It makes no sense to me. That was the original reason that made me change the front pulley, in case the markes were wrong, but no change.

Just a thought, you do have the correct valve timing don't you? Not just on the chain wheels but the theory - IOW the BJ8 camshaft didn't use a different set of timing wheels - also are you sure that your distributors mechanical advance isn't broken, such as either weak or broken springs. Also, as (IIRC) Dave mentioned, make sure than the water pump is actually pumping water around the system.

Of course.

Gmack

A blown head gasket will do this... If it's blown between a cylinder and the water jacket...

SteveL

Then there shouldn't be any corrosion of the cast iron block - unless you had to do lots of topping up introducing fresh aerated water.

The Valve timing was my thinking, so I took of the front cover; that was were the first confusion came in, as the w/s manual says"valve timing marking...... adjoining teeth are marked" to me that is similar to the "A" series, where you set both sprockets so that the dots are next to each other. Not on this engine, they never come close to each other! later in the book it shows how to set both cam and crank keyways to vertical and position the dots on the srockets with 14 links between them, and slide them on with a bit of wriggling back and forth. That is how they are positioned; and then by checking the point of valve opening against the marks on the front pulley it is about right as far as I can tell The distributor is new, and with the cap off, I can see flow across the header tank, (once the thermostat has opened)which increases if I blip the throttle. But the Electric Fan never switches off (well, it didn't before I started to investigate) and temperature increases untill I get worried and switch off.

That's not what I asked or suggested, forget the marks or keyways, actually check the crank TDC and the actual valve over-lap timing etc. your timing wheels could be wrong, your keyways could be wrong - check the theory against the spec' (*for the BJ8 camshaft*).

New since the problem or just new?...

and with the cap off, I can see flow across the

Have you had the water pump off to check that all the impellors are capable of doing work, I've seen pumps with corroded / missing blades.

With problems like this don't trust anything, don't assume anything!

I should have added that this is going to have to be measured with a timing protractor and DTI gauge, it doesn't take many degrees for a valve to be cracked open whilst the problem won't be that noticeable to start with but as the valve and seat start to wear or burn...

I tried to explain in an earlier post; To measure the valve timing, I am rotating the crank until the pushrod is just binding; This give a very wrong reading. Later I found in the book it says Rocker clearance for valve timing: .030" So my understanding is: reset the rockers to 30 thou to check valve timing; this gives an almost correct reading, within 5 degrees, so with the inaccuracy of turning the crank 5 degres at a time this is OK.

The distributor is a Mallory twin point system, designed to go with the BJ8 cam, fitted at about the same time. When it was fitted, the car did not overheat, at least for the first 2 years. But if when I get it running again tomorrow it is still overheating, it is easy to re-fit the original one.

The water pump was replaced some time ago; it is off for inspection now( as it is easier to get the bolts out for the timing cover) no signs of impellor damage and block looks free of sludge.

OK, Understood; that will have to wait; I'll run it again to see how it performs then if needed, get hold of a protractor.