Hi All,

So i've been for a spin around the block today to get some petrol ready for the MOT on Wednesday and the engine isn't running that well, its driveable but the timing is definitely off.

I've spent a fair bit of time over the last few days trying to find details of what the timing should be with the engine running as all the books just give static but so far I haven't had any success.

Where I did find references the contradicted each other and it wasn't clear whether the figures quoted were at engine speed or distributor speed which is half engine speed.

The engine is a 3.8 in a MK2 with an 8:1 compression ratio, its completely standard apart from a 20thou rebore.

The reason I want to do it dynamically is the engine had no marks on the front pulley for timing but it did have the pointer on the sump so when I put it together I marked the pulley at TDC on no 1 and no 6. I have access to a timing light which enables me to put in the required timing and then time off zero.

Any ideas on what I should be setting it to for a start?

Also any idea what the mixture should be set to on a CO meter? Answers I have found so far suggest starting at around 5.5%.

I appreciate that the above will be a good starting point and then I might need to make minor adjustments.

 

It's a long time since I had my Mark 2, (sold 1988), so maybe best to have a read here: -

https://jec.org.uk/forums/viewtopic.php?t=8861

 

Hi thanks for this, this is one of threads I read through before I posted and it just ends by saying he set it to 10degrees BTDC but it doesn't say what engine speed he did this at.

Should also have said that my engine has the earlier distributor DMZ6 or somthing like that.

 

Timing is set at idle with the vacuum advance disconnected and blocked off at the carb.
At idle the advance weights are not coming into play and that's what you want.
With out checking idle is 600 to 650 rpm.
Timing procedure is also done on a fully warmed up engine.

 

So if I set it to 10 degrees at idle of around 650-700 that should be a good start?

 

Static timing should be 7deg BTDC, at 650-700 rpm, you should be getting between 2 and 6 degs of centrifugal advance, so 10 deg at 650-700 rpm would be about right.

There is not much info about timing light figures, manual states static timing, you can then use a vacuum gauge and the distributor figures to work out the dynamic figures, but these can vary by a few degrees from one distributor to another.

This quote from JEC is a pretty good description of how to set one up for tune, as todays fuel is more prone to detonation and pinking, any figures states historically are no longer accurate as they should be retarded a deg or 2 anyhow.

Quote from JEC forum:-
"In my experience with carburetted cars it is best to set the timing initially with a vacuum gauge. Disconnect the vacuum advance pipe from the carb and connect the gauge. With the slowest tickover and balanced carbs, slacken the distributor and turn until the highest vacuum reading is achieved. If the tickover rises significantly the slow it down and recheck the vacuum. Then road test for pinking (detonation); if pinking is present due to poor fuel, wrong heat range spark plugs or carbonated valves/chambers, then retard a degree at a time, using a timing light, until it stops."

 

I'd set it statically then just advance the timing in small increments untill it starts pinking then back it off a tad.

 

Homer if there is a timing pointer there are marks on the damper if it is the correct one. They may be difficult to see and you may need to clean and scrub a bit--but they are there.

 

I have the same situation with the damper and a timing pointer. When I rebuilt my engine I was surprised that there were no timing marks on the damper to indicate how far advanced or retarded the engine would be. I put a mark for TDC on the damper, aligned with the pointer and then used a degree wheel to add the necessary marks. I don't know if the damper was poorly marked when manufactured or if they were never put on some dampers.

 

Something fishy here . . . my first reaction was 100% behind George . . . any and EVERY early XK engine (ie the "silver tops" pre XJ6) that I ever worked on (and I guess 50 or more) had notched/marked dampers. TDC brought the pointer into alignment with the tiny notch, while the far less legible BTDC markings would be "spotted" by most shops with a tiny dob of white at the appropriate static setting . . . or, somewhat more advanced as stated, for use of a strobe gun at idle with vac disconnected and plugged.

So, early XKs with TDC pointer but a damper with no markings? Is there any evidence the damper has been replaced . . . perhaps with a later one where flywheel timing marks were used instead of damper marks?

In any event, I would be creating them if they really are absent. Use a dial gauge with an extended pointer to reach the piston via #1 spark plug hole and rotate engine to gain an absolute TDC. Mark damper alignment with pointer, rotate engine so you can file a clean sharp mark, then re-test alignment. Bend pointer to adjust for perfect alignment. Careful maths will reveal the correct BTDC scale.

So, there you go . . . 50+ years spanner twirling and you learn something new . . . or will a more careful inspection of those dampers reveal a tiny notch gummed up with years of accumulated dirt? Very interested in results.

Cheers,

Ken

 

Ken, When I rebuilt my engine, I thoroughly cleaned everything, including the damper and was looking for marks that should have been there. Otherwise, why would there be a pointer. The thought also occurred to me that the damper may have been replaced at some point in time.

 

Yes, Ted, I agree and this was also the combined view of several others here at our local club meet today. One mate (!) pointedly suggested that the vast majority of those I had experienced was back in the day . . . and, drat, he was right. Taking the late 70s - early 80s as an average, I now figure that 30-40 of those 50+ I had worked on were about 35 years ago. Many of those may no longer be alive, but those that are, as is being discussed here, are perhaps 50-60 years old and no doubt, have been candidates for damper replacement.

On that note, I suddenly feel old. Maybe an afternoon nap will help?

Cheers,

Ken