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

[nicrguy1966]

40 minutes ago, Ian Foster said:

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

It's a long standing issue that any time anyone has ever tried to set my ignition timing correctly, the car is virtually impossible to drive, until the timing is reset 'by ear'.

It's only recently I've discovered how far from spec. my timing needs to be set to actually go.

I'm looking forward to checking the cam timing. I'm sort of hoping it's wrong, although that will be a fair amount of work to fix.

If it isn't that I'm pretty much out of ideas!

Edited August 21, 2023 by nicrguy1966

[johny]

Oooh could be another 50 horses available😍

[nicrguy1966]

21 hours ago, Ian Foster said:

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

Longstanding, but I only recently discovered just how far from "spec" the ignition needs to be for the car to run smoothly.

I really hope the cam was installed incorrectly, as I'll be expecting a big boost of power once it's fixed (and better MPG)!

Edited August 22, 2023 by nicrguy1966

[johny]

Orrrrr you might have accidently found a set up that boosts power over the standard output😳

[nicrguy1966]

14 minutes ago, johny said:

Orrrrr you might have accidently found a set up that boosts power over the standard output😳

That would be quite upsetting!

Having a car that runs as Triumph intended is nice, but it will be incredibly annoying if after hours of work, it runs less well with the cam in the right position! (assuming it is currently in the wrong position)

[johny]

Youll be able to sell the secret cam position and timing far and wide though....

[Pete Lewis]

do make sure you have tested /measured/cussed and swore to find what you have before you go jumping into untested territory

based on any bright ideas we have posted ,   

Pete

[nicrguy1966]

6 minutes ago, Pete Lewis said:

do make sure you have tested /measured/cussed and swore to find what you have before you go jumping into untested territory

based on any bright ideas we have posted ,   

Pete

Don't worry, I'm very much a "if it ain't broke, don't fix it" type owner, which is one of the reasons this problem has been ignored for so long. I'll be making damm sure the cam is in the wrong position before I start dismantling anything!

[Pete Lewis]

Ha  Thank heavens for that 

Pete

[nicrguy1966]

Ok, the latest chapter of my saga.

I did the check on cam timing using the "rocker method" (as described in the workshop manual), and there might be something wrong. Assuming I did it right, after setting the gaps to 0.04" on 1 & 2, then spinning the crank around to TDC, the gaps were not the same. #1 had no gap, and #2 0.004".

I did it all twice just make sure I didn't just make a mistake setting the gaps to 0.04".

I've reset the gaps to 0.01" on all rockers and put the car back together as I need to use it next week.

Does everyone think the timing chain cover needs to come off?

Any other suggestions before I start such a major project (I assume I'll have to drain the cooling system and remove the radiator before I even start to try and remove the nut on the end of the crankshaft, and do I even have a spanner/socket that size?).

Also, huge thanks to everyone that's offered suggestions so far, it's been a real boost to my confidence.

[johny]

Not sure you got the procedure quite right as of course theres two TDC positions for piston 1. After setting the gaps I would have turned the engine until valves 1 and 2 are in rocking position and then see where your pulley indication is (TDC firing)....

[johny]

Either way (TDC exhaust would have had both valves open) I think theres something wrong with the valve timing so yes drain coolant, rad out, pulley off and then cover. Check chain/sprocket and crank seal ring condition, replace tensioner, gasket and seal? Using manual set valve timing and ensure cover fixings are put back in correct places...  Then drive off into the sunset at max power😁

[nicrguy1966]

Very good point about 2 TDCs.

Now you've put some doubt in my mind if I did it right. If the crank was on the exhaust stroke, the exhaust valve would be wide open at TDC, and I'm pretty sure both were closed. But, before I start taking the engine apart, I'll do the check a 3rd time, maybe the way you describe this time (finding the rocking position, rather than setting to TDC).

The earliest I'll have time is Monday, so another installment will follow!

[JohnD]

johnny, mrnice,

Yes, during the four stroke cycle, the piston comes to TDC twice.      It's better to think of the datum point as TDC on the firing stroke.    It removes confusion. 

Think of the cycle starting at TDC.  The inlet valve starts to open, the piston descends.     It then return to TDC and the spark plug fires - this is the firing stroke, with both valves closed.    At the end of the firing stroke, around Bottom Dead Centre the exhaust valve opens, and as the piston ascends the exhaust valve begins to close.    It isn't completely closed until just after TDC, while the inlet open just before.     This is called "overlap", and is important to promote clearance of the burnt gases and induction of the new charge.

Obviously, at TDC on No.1 on the firing stroke, both valves will be (should be) closed.      Because 1 and 6 move together, but 360 degrees apart in terms of their cycle, at the same point the valves at No.6 will be slightly open, "on the rock" as they overlap at the end of the four stroke cycle.    

Mrnice, 

At NO point in that cycle will the exhaust valve, or the intake, be open at TDC!   

But your findings that at TDC on No.1, having both valves closed, and so on the firing stroke,  then the valves at No.6 were unequally open, indicates that the camshaft is not set correctly.  

 

OMG!   I've just read your post above!  "I did the check on cam timing using the "rocker method" (as described in the workshop manual), and there might be something wrong. Assuming I did it right, after setting the gaps to 0.04" on 1 & 2, then spinning the crank around to TDC, the gaps were not the same. #1 had no gap, and #2 0.004".   My emphasis.   You set the gaps wide on valves 1 and 2?   That are on cylinder no.1?     That would be completely wrong!

Please reread the manual!    Have I suggested that you read my article on 'Equal Lift on Overlap', over on Sideways?   See:  https://sideways-technologies.co.uk/forums/index.php?/topic/7770-equal-lift-on-overlap-the-other-cam-timing-method/#comment-102165 )

That assumes you have two dial gauges, which you may not have, so may I also suggest that you look at a later addition to that article: https://sideways-technologies.co.uk/forums/index.php?/topic/9639-a-new-method-of-cam-timing/#comment-134275   which only requires a 'Combination set square' with  a protractor and spirit level.

You can get one of these for about a tenner. n  Its the centre part that is needed.  The other fittings are useful but not for this!    Meanwhile, there are many videos online about the four stroke cycle and valve overlap.  May I suggest you watch some, to help your understanding?

John

PS Online video, with the legendary Mark Field, and another guy, rebuilding a GT6 engine: 

 

Edited August 26, 2023 by JohnD

[johny]

My emphasis.   You set the gaps wide on valves 1 and 2?   That are on cylinder no.1?     That would be completely wrong!

One of these quotes has to be right....

[nicrguy1966]

25 minutes ago, johny said:

My emphasis.   You set the gaps wide on valves 1 and 2?   That are on cylinder no.1?     That would be completely wrong!

One of these quotes has to be right....

That's the manual I was following. The quote you shared says adjust number 1 (and later number 2) rocker. But you're saying I shouldn't have adjusted rockers 1 & 2.

I'm confused.

[JohnD]

That makes my head spin!

"No.12 push rod at highest point" means that the piston is somewhere below TDC.   I don't understand how that can achieve correct timing.

In contrast, I offer a similar but very different method  from the "Brown Bible" my copy of the original TR6 WSM.    Apart from capacity this engine is identical to 2L GT6 engine, and the method starts with setting the crank to TDC on No.1 on the firing (compression) stroke.

 

You may also wish to consult this page from the Spitfire WSM, Page 12.41.05.  OK, it refers to a four cylinder engine, but the method is as above:

 

Did I suggest above, Mrnice, that you contact your local TSSC Area Group?    As so many students have found in the last few years, teaching online is not as good as face to face learning !

John

 

Edited August 26, 2023 by JohnD

[johny]

The manual is just using the rule of 13 (six cylinder) so you have valve 1 on the back of its cam when valve 12 is fully open. Here though we're then adjusting tappet 1 to 40 thou for the purposes of using the rocking method to set cam timing which, as you know, means valve 1 and 2 cam lobes should be at the same heights at TDC cylinder 1... 

[nicrguy1966]

I'm starting to think we're reaching the "too many chefs" point of the conversation.

I'll take the rocket off and have another play on Monday (hopefully), but I'm just getting more confused what I'm meant to be doing.

Maybe time to drive to a garage with a qualified engineer.

Edited August 26, 2023 by nicrguy1966
Typo

[johny]

Follow the manual, its not perfect - there are some minor errors and easier ways to do things but it'll get you there. You almost did it perfectly first time but then deviated at the last minute😁

[Wagger]

1 hour ago, nicrguy1966 said:

I'm starting to think we're reaching the "too many chefs" point of the conversation.

I'll take the rocket off and have another play on Monday (hopefully), but I'm just getting more confused what I'm meant to be doing.

Maybe time to drive to a garage with a qualified engineer.

These guys have it correct. Qualified and old Engineers. Download the procedure from the workshop manual. Others have posted it before.

[nicrguy1966]

Just to (hopefully) clarify that I'm not a total idiot, this is why I span the crankshaft to TDC after opening the gaps on rockers 1 & 2:

 

[johny]

Yes I think youve demonstrated the problem but by putting the cam in the rocking position you'll be able to see how many degrees away from TDC the crank is. This might even give you an idea of whether youre a tooth, half a tooth or even a quarter of a tooth out on the cam sprocket... 

[johny]

Did you say it had been like this since engine rebuild? In that case new sprockets and chain could have been used which of course come without timing marks so making it easier to get wrong. Then you'll have no option but to use the rocking method to get it correct👍

[johny]

I make it about 34º of crank rotation for each tooth out on the cam sprocket so youre probably going to have to adjust the latter by less than a tooth...