Hot cylinders 1 & 4

Hi, no cam alignment tool but really I just wanted to check they weren’t 180° out. I think next step will be to have the mixture settings checked at a classic car garage. Fuelling wasn’t high on my list of likely causes, but there doesn’t seem to be much else left !

The alignment tools are pretty cheap. If this engine has been apart and you have the cam covers off already it would be a good time to check. Really tuning these carbs doesn’t take any more skill than what you have already done so far. Just need to follow the manual. Check dashpot oil levels, check float levels, check jet height, balance the aur flows. Don’t know where you live but it might be easier to do yourself than pay someone else to learn how to do it…

Hmm ! It has Triple SU HD8’s. I’d do it on a twin setup, I did my MGB 40 years ago, but I have developed a hatred of multiple carbs after ownership of many Japanese motorcycles. I suspect you may also be correct however, in that who ever I take it to will be learning on the job.

On eBay. Cam tool is $10. Unisyn carb air flow tool. $25. I assume you already have a timing light. All else you need is a service manual and some patience.

Moral support to attempt the black arts ! I know in my heart your are right. :roll_eyes:

I started the procedure detailed in the manual for SU HD8 carbs. It refers to checking pistons fall freely with a clunk ! They do not ! Well perhaps the front one does, but middle and aft are progressively less solid feeling somewhat spongey and loose. Is that just the lifting pin though ?

Not likely, you’re gonna have to maybe swap domes around and or check the fit of the jet and needle to see if something there’s interfering.

It means they should fall easily without the slowing effect of the oil damper inside the piston. Did you remove the damper devices from the domes for the test?

I am now suspecting the quality of the ignition. The coil is not original equipment and I have ordered a new ignition module for the amplifier. Am I correct in thinking even if the other two components of the amplifier were defective ( the capacitors) that shouldn’t really affect the strength of the spark as one is to protect against over current and the other is to cut out radio interference ?

OK, so after I decided I had tried everything possible, I looked for an outside opinion. Took it to a classic car garage and it seems the answer is, there is no answer ! I had the block flushed, new core plugs, timing and carbs set professionally. The car does now drive way better, but the temperature discrepancy is still there. I guess it’s an anomaly I will have to live with !

Interesting that it’s the rearmost cylinder on each exhaust manifold, maybe something to do with the manifold shape.

This may make you feel better about it. This is an IR photo of my manifold. I searched high and low for a cause of the apparently “cold” rear cylinder. I equipped the engine with O2 sensors, and tuned the carbs to within a hair of perfect. But it remains a mystery.

Could be a coolant flow indication

That’s a great photo and yes it does make me feel better thanks :blush:. I had the block flushed too, so I don’t think coolant flow plays a part. I think it’s just the exhaust gas flow and the shape of the manifold and headers.

Could also be due to varying thickness of the casting walls, obviously cooler where its thicker.

I couldn’t give up on it. A new line of enquiry occurred to me. I checked the valve clearances and they are nearly all way too tight. Also the bracket that holds the timing chain sprocket has broken on the exhaust side so it’s only supported at the cam side ! As the Cams have to come out to do the valve clearances, the head will also come off to replace that bracket. :crossed_fingers:I really think this might solve the problem.

Part 18 in this diagram, the upper right has snapped off ( and been removed by a previous owner).

Not a serious problem. It’s only used to hold the sprockets when fitting or removing the cylinder head. It serves no function after the engine is assembled. At that point the sprockets are supported by the cam flanges.

Thankyou ! That means I can just get the valve clearances set properly, which is way much less of a job.

Before I start on the Valve Clearances I have a couple of concerns, mainly about refitting. My manual doesn’t give torque settings for the bolts holding the timing chain sprockets to the cam lobes ( there are two bolts on mine) It just says they should be wire locked. Also the timing chain tension seems wildly different on the inlet and exhaust chains. The inlet is bar taught, but the exhaust I can move about 1/2 cm with a screw driver. The manual doesn’t really stipulate how much tension there should be, and as it’s the same chain looping round both sprockets and there’s only one tensioner, I don’t see how they can be different ?