GT6 Mk3 only runs well with VERY advanced timing. Any ideas why?

[Pete Lewis]

you can write a private e mail from the email tab in you profile

pete

[nicrguy1966]

26 minutes ago, JohnD said:

Believe it or not, the Post Office does provide an excellent service, even to those parts of the UK that do not speak 'Received English'.

John

I dread to think how much it would cost to post a GT6, even second class 

[Pete Lewis]

you can send a private e mail from this site  either from your profile  page or the envelope icon on the top blue header 

or click on the members avatar to get the e mail 

Pete

Edited August 17, 2023 by Pete Lewis

[JohnD]

Nicr,

I can't test your entire car. much as I'd like to.  Post me your crank pulley, which weighs 1600 grams and would cost (with less than 400 grams of cardboard) a bit over £6 First Class .

John

[nicrguy1966]

2 hours ago, JohnD said:

Nicr,

I can't test your entire car. much as I'd like to.  Post me your crank pulley, which weighs 1600 grams and would cost (with less than 400 grams of cardboard) a bit over £6 First Class .

John

That makes a lot more sense than my idea!

Hopefully it will not come to that. First I need to inspect the pulley, then try setting the crankshaft to TDC then see what the timing indicator position is.

After that, maybe I'll think about removing the pulley, but it's something I'd prefer to avoid, especially as the car is currently drivable with its weird timing advance setting.

[JohnD]

Indeed! Good plan!

[nicrguy1966]

Update!

I did a few tests this morning. 

1) The timing marks seems fixed firmly to the pulley. No way I could move them in either direction, even with a screwdriver wedged into the TDC marker.

2) With the plug out of cylinder 1, I could easily feel the piston position with a screwdriver and although it doesn't move much at the top of the stroke, I could easily detect movement around 10 degrees before and after the TDC mark. So it seems the TDC mark is in the right place.

3) This time I took a photo of the strobe at idle (a smooth 650rpm). The mark is showing more than 20 degrees BTDC. 

4) When rev'ed to 2000rpm, the timing mark is so far advanced, it's not visible from the angle the photo was taken at, so maybe 40 degrees BTDC! Even when set 'by ear' and running smoothly,I have noticed a lack of power at high revs and open throttle (e.g. accelerating from 50 to 70 in top gear).

5) When removing spark plug 1, I noticed the mixture was a little rich. Nothing too extreme, but worth noting. I would have expected a lean mixture given the K&N air filters.

So that's all the latest news. Any idea what to try next?

Edited August 19, 2023 by nicrguy1966

[Pete Lewis]

cam timing or dodgy strobe  ??

[nicrguy1966]

1 hour ago, Pete Lewis said:

cam timing or dodgy strobe  ??

I don't think it's a dodgy strobe as whenever anyone tries to tune the car with a strobe it ends up awful, not just me.

I assume I'd have to remove the timing chain cover to check the cam timing?

[johny]

You could do it from the cam sprocket marks or the rocking valve method as described in the workshop manual which uses the position of cylinder 1 inlet and outlet rockers at TDC to indicate correct cam timing...

[nicrguy1966]

35 minutes ago, johny said:

You could do it from the cam sprocket marks or the rocking valve method as described in the workshop manual which uses the position of cylinder 1 inlet and outlet rockers at TDC to indicate correct cam timing...

I'll do some research!

[RedRooster]

1 hour ago, johny said:

You could do it from the cam sprocket marks or the rocking valve method as described in the workshop manual which uses the position of cylinder 1 inlet and outlet rockers at TDC to indicate correct cam timing...

What he says. 

RR

[Pete Lewis]

yes can be done from the rockers   no need to strip anything  down 

just need feelers 1/2"af spanner and screwdriver  follow the manual 

or we can spell it out if thats helpfull

Pete

[Pete Lewis]

all this  but why?????       has the car had a long standing problem or has a problem arrived out the blue ????

{Pete

[nicrguy1966]

30 minutes ago, Pete Lewis said:

all this  but why?????       has the car had a long standing problem or has a problem arrived out the blue ????

{Pete

It's been a problem I've been ignoring for years, but something's not right and if I can fix it, I'd like to.

A problem is still a problem even if it's old.

The first job is to work out why the timing is so extreme.

Edit: If I fix it, I'm hoping for better performance or better MPG, or maybe both.

Edited August 19, 2023 by nicrguy1966

[Pete Lewis]

a vacuum  gauge on the inlet manifold gives a good indication of timing and general running needs an idle reading around  18 -21 ins /hg 

doing a simple rocker cam timing test is worth reading up on  as the chain wears the cam timing gets later but that wont upset ign  as you just turn the dizzy to accomodate the changes 

the tensioner is on the slack side of the chain so as the links and pins wear the drive side gets ...longer and cam gets later 

all these things help if performance is diminishing 

Pete

[nicrguy1966]

On 19/08/2023 at 17:35, johny said:

You could do it from the cam sprocket marks or the rocking valve method as described in the workshop manual which uses the position of cylinder 1 inlet and outlet rockers at TDC to indicate correct cam timing...

I only have the Haynes Manual, not the official Workshop Manual, and as far as I can tell, it doesn't contain anything about checking the cam timing using the "rocking valve method". Do you know if a description of this has ever been published online?

[johny]

Ah you need the free to download bible kindly offered at vitessesteve.co.uk

[Pete Lewis]

basic rules are you turn engine so rockers 11 &&12 are on the rock/in balance  (one going down one coming up) 

set rockers  1 &2   tappets to 0.050"   turn engine  to align TDC for no1 on compression   and then measure the tappet gaps on the wide setting   doesnt  matter what the gap is so long as they should both be the same /equal .

any variance needs a bit of chain/sprocket twiddling on another day 

the cam sprocket has 4 holes and the sprocket can be turned over this will give each fixing at 1/4 tooth  adjustments increments.

so with a good pair of glasses and six hands its quite easy and adjustable if its needed 

Pete

[nicrguy1966]

1 hour ago, johny said:

Ah you need the free to download bible kindly offered at vitessesteve.co.uk

Downloaded, and I've found the section on checking the cam timing. 

This will be very useful in the future, not just while I'm scratching my head over timing advance.

Thanks for the link.

[nicrguy1966]

43 minutes ago, Pete Lewis said:

basic rules are you turn engine so rockers 11 &&12 are on the rock/in balance  (one going down one coming up) 

set rockers  1 &2   tappets to 0.050"   turn engine  to align TDC for no1 on compression   and then measure the tappet gaps on the wide setting   doesnt  matter what the gap is so long as they should both be the same /equal .

any variance needs a bit of chain/sprocket twiddling on another day 

the cam sprocket has 4 holes and the sprocket can be turned over this will give each fixing at 1/4 tooth  adjustments increments.

so with a good pair of glasses and six hands its quite easy and adjustable if its needed 

Pete

Another project for next weekend!

Even if this doesn't reveal anything wrong, it's a good excuse to check and adjust the tappets, which haven't been done for a while.

As always, I'll report back once I've done the work and washed my hands!

[Pete Lewis]

general tappet adjustments are use rule of 13  and 0.010"  on a cold engine 

rule 13   1 down  set 12      10 down set 3   etc 

if the rocker pads are worn then feelers will bridge the wear and give a false feel to the feeler fit 

Pete

Edited August 21, 2023 by Pete Lewis

[nicrguy1966]

3 minutes ago, Pete Lewis said:

general tappet adjustments are use rule of 13  and 0.010"  on a cold engine 

rule 13   1 down  set 12      10 down set 3   etc 

if the rocker pads are worn then feelers will bridge the wear and give a false feel to the feeler fit 

Pete

I had a reconditioned engine fitted about 15 years ago (with hardened valve seats for unleaded petrol), so there shouldn't be 50 years of wear to worry about, and those 15 years haven't been high mileage.

I wonder if my timing issues originate from that engine swap? I probably drove it for several years trouble free without ever checking the ignition timing.

[Pete Lewis]

hardened seats only go on the exhaust seats   thats fine  

but has nothing to do with the rocker pad that wears where it rubs the head of the valve stem 

 and makes a groove in the rocker pad this makes a normal feeler a poor fit at judging the real gap

Kickadjust make a ratchet socket and driver but they are fiddly an need an accurate gap in the first to set up the clicks  ...pretty useless but a good idea of sorts 

wire pin gauges are best but  try to find them ....no hope 

have fun   keep on this   one day all will be revealed    ....well  !!!

Pete

[Ian Foster]

2 hours ago, nicrguy1966 said:

I had a reconditioned engine fitted about 15 years ago

It is possible that the cam was installed incorrectly. The check procedure will show if it is out.

Ref Pete's question above, is this a new or longstanding issue?

Ian