Even more Sereis 3 troubles

Good afternoon.

Sorry to be pestering about this problem, but i am still drawing blanks.

series 3 2.6 litre straight six. i rebuilt carbureutor, put new set of points and condensor and the motor is in excellent mechanical condition. it is getting a good strong spark from each cylinder and the vacuum advance is working. when motor is revved, timing advances by about 10-15 degrees. but the problem remains, the manifold is still glowing red hot after about 10 mins of driving at 80ks an hour on flat.

i have played with timing, tried it from about TDC all the way through to 20 degrees BTDC, played with the mixture, all the way from lean as it will go to just before the setting screw falls out. at settings, the motor runs reasonably smoothly, but still has the glowing manifolds. the motor is still staying within it's normal operating range, which is quite cool.

the one last thing i can think of is fuel. it is built to run on leaded fuel but up til now i have been running it on unleaded without putting any additive into it. i know i'm probably gonna cop a bit of flak for this, but i was under the impression that running it on unleaded would simply accelerate valve wear etc. a friend told me that it can infact cause the valves to get hotter, thus causing the manifold to get hot.

so my question is thus, will running a motor designed for leaded on unleaded cause the exhaust manifold to get extremely hot??

if so, i will fork out the extra 10 cents per litre for the premo unleaded. grumble grumble. but i will putting it on gas soon anyway!!

/thanks in advance.

Sam.

Reply to
Samuel
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Samuel came up with the following;:

Dunno ...

... So why not try that anyway ?

I'd also look at the mixture and any needle jets in the carbs. If the zorsts are glowing ISTM that it's just as likely to be a mixture problem. Make sure the air or fuel flow isn't restricted in any way, and check the back end of the exhaust that there isn't half a ton of concrete, or similar crud, stuck in the tailpipe.

Reply to
Paul - xxx

I just put half a tank of 98 octane premium into it but there was already half a tank of the normal petrol in it. i also chucked a load of the valve-saver stuff in it. i drove this hard up quite a long hill and the manifold seemed to be glowing less, but there wasn't a great deal of time for fuel to mix etc. and judging the "glowing-ness" of an exhaust manifold late at night in the cold and rain when you've just had to turn back from a weekend away because the bloody cars is causing trouble is a little subjective and prone to errors.

the side-draught stromberg 175 cd has only one mixture adjustment screw and i have tried it with mixture set at both extremes with similar results. fuel-pump works well, and air supply seems to be good. i have also checked the exhaust and it all seems to be free of obstruction, no bananas or potatoes up the tail-pipe. i did a lap around the block without the muffler, for "investigative" purposes of course, and boy does it sound Beefy. i love it!! almost tempting to leave it off all the time.

Sam.

Reply to
Samuel

Sam,

If you want to know if the mixture is right take out a plug and look at the deposits on it. You want a nice tan colour. I'm sure if you search there will be pics up somewhere for comparison.

I don't know if you should put premium grade fuel in. I think the engine was designed/tuned for 2 star (low octane) fuel.

It will either be timing or mixture - and you are right to worry - your exhaust valves will be history soon.

choo

Reply to
sneezy

so Samuel was, like...

How are you setting the timing? I'm pretty sure that it should be set to between 6 and 0 degrees BTDC (depending on model, CR, territory etc) if you are using the static method, but ISTR that if you use a strobe and tachometer to set the timing at idle speed (~500rpm) it should be something like 6 degrees ATDC. Prepared to be shot down if I'm wrong on this.

Never heard of this. The action of lead (or an additive) in the petrol is to physically cushion the action of the valves hammering against the seats. It has nothing AFAIK to do with combustion temperature. Again, ICBW.

I doubt it.

HTH

Reply to
Richard Brookman

You know I shall have to take a look at my manifold some time to see if it is doing that as I run on cheapo unleaded only. I have got to sort out my own overheating problem eventually as one day that needle is going to go a little too far over but just have not had the time or the inclination lately

Reply to
Larry

Thinking sideways a bit .... have you verified the accuracy of the timing mark that you are using for TDC? It is possible that someone in the past has reassembled the parts incorrectly - even fitted wrong parts. (They might not have used the marks to set the ignition timing but you wouldn't know that).

Is this a new problem - i.e. did it work before but does no longer? What changed? If I've picked up the right thread, manifold overheating was not the original complaint (perhaps it just wasn't mentioned). It seems that the overheating manifold only appeared after you tried timing adjustments so that must be the most suspect area.

The suggestion to observe the plugs to check the mixture is a good one.

Reply to
Dougal

The lead stops the valve seat burning out. So if unleaded is used and the valve seats are soft the valve sits further into the seat. This then reduces the valve clearance. So when the valve is hot it lengthens, with no valve clearance it never seats, so hot burning gases get into the manifold.

AJH

Reply to
sylva

There must be something wrong with the carburettor if moving the mixture screw either way has no effect. If you want I can e-mail you the manual pages on carburettor settings to check.

Have you checked for air leaks around manifold or servo and are the exhaust valve clearances ok. As others have said, it must be either timing retarded or weak mixture.

Martin

Reply to
Oily

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