Cylinder Head Woes

[henda]

Hello,
Searched the forum couldn't find a similar subject.
I'm after a bit of advice please, my car started missing when accelerating and giving a slight backfire. I have had the car to a garage that I use who has checked the carbs, timing, fuel etc. Everything is spot on, the same as he set it up last year and afterwards it ran like a dream up until now.
He seems to think that it may be a sticky valve or worn valve or valve seat. First question is I'm wondering has anyone else experienced this? What was the outcome? and what would a rough cost be to refurb the cylinder head?
The other dilemma is that he checked the compression in each cylinder and all were very similar however they had a lower compression that expected. I'm just wondering if it is just a case of a head refurb and valve inserts or its an engine out and full engine refurb.

[mgcjag]

You have a S2...the head studs are long and go right through the water jacket of the block....its not uncommon for these studs to snap when trying to remove them.....so it isn't just a guaranteed "lets just pull the head off"....you need to be aware of possible consequences of going down this route....does your garage specialise in classic Jags....I would be looking at electrics very thoroughly first.
Clean and re crimp or solder all the low tension connections and try a new coil, dizzy cap and rotor arm from the distributor Doctor.....Steve

[malcolm]

Not sure how much I’d worry about the compression if they are roughly the same and it ran well before. My compression was lower than “normal” after a head refurb and it went like a train. I’d check much more as per previous post before going the head off route.

[Allrand]

I did you do your compression test when the engine was hot or cold? Does the car smoke? Squirt some oil down the bores and test again. If there's an improvement it could mean some wear on rings or bores but if it's not significant leave well alone.

[abowie]

You need to do a leak down test.

Having said that, I tend to agree with Steve that your problem is electrical. One at a time I would be replacing points if fitted, cap, leads, plug caps if fitted, condenser, coil etc

[chrisc261]

Hi,
I had a similar problem on my 3.8, tried absolutely everything, fuel pump, distributor (123), plugs were about a month old so did not try those. Took it to a specialist garage, and they tried everything I did - compression test etc. It turned out to be a dodgy spark plug, even though they were new and from a reputable supplier. The plugs were NGK. Upon research there seems to be quite a lot of fake NGK plugs about. So I would say check the plugs. If it is backfiring it sounds electrical. I hope you find this helpful.

[malcolm]

What electrical system do you have? Standard dizzie, 123, or standard but with electronic points? (Like Pertronix)
I ask because I had a missing engine under accleration at higher revs, despite all electrical components being new. I had Pertronix - type points. I had standard plug leads which interfere with Pertronix, powerspark etc, and was told to change them for Silicone leads which don't build up a field - problem instantly solved.

[henda]

Morning,
Thanks for all the feedback, the car has a 123 dizzy which was fitted last year, I've replaced the leads with a set from Martin Robey, however they are not silicon, that said they haven't made a difference. Interesting comment about the spark plugs, fingers crossed I will try that today. The garage I use said that it was backfiring through the inlet and exhaust port. I was speaking to a friend the other day and he came up with a great idea of using a small camera to have a look at the valve seats. He also thought that it may be a broken valve spring does anyone have any experience or thoughts on this.

[chrisfell]

I’d double double check the timing of the 123. First check the timing pointer is correctly indicating TDC, then I’d use a timing light to check both static and the advance curve. It sounds like the timing might be quite wildly advanced. On S1s this is a pain in the neck as the timing pointer and the marks on the damper are under the car. Dunno if this was improved on the S2.

[henda]

Hello
Unfortunately no its still on the bottom of the engine, however I do have my new lift now which will make things a lot easier.

Many Thanks

Paul.