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

[nicrguy1966]

57 minutes ago, johny said:

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... 

Thanks. I'll be having another go on Monday (assuming the skin grows back on the hand I was using to pull the fan belt to turn the engine). 

If I understand you correctly, my tests today confirm that the cam timing is off, and finding the rocking position will tell me how much it's off.

Onwards and upwards!

[johny]

Ouch yes maybe easier without plugs in especially for fine adjustments🙂

[Pete Lewis]

why not put in 4th  jack rear wheel and turn from there  might save the knuckles  or just push the car in gear 

Pete

[nicrguy1966]

19 minutes ago, johny said:

Ouch yes maybe easier without plugs in especially for fine adjustments🙂

I thought I was being clever not risking getting the spark plug leads mixed up, but with hindsight...

I could just have labled the leads!

Edited August 26, 2023 by nicrguy1966

[johny]

If the valve timing is confirmed to be wrong have a think about how to adjust it before starting. Heres my thoughts:

Assuming the sprockets arent marked youre going to have to be careful to keep everything aligned. I would turn (always normal direction of rotation) the engine to TDC and measure the clearances on valves 1 and 2 (having previously set them to 40thou). Then very carefully remove the pulley and cover and, checking you still have the same valve clearances, mark the positions of both sprockets relative to the backplate.

Next is the delicate bit as the crank musnt move while you undo the cam sprocket and remove it along with the chain. Once thats removed, temporarily put the sprocket back on in the same position and use it to turn the cam to its rocking position as indicated by equal valve clearances - again mark its position relative to the backplate. Use the loose chain pulled tight on the right hand side of the sprockets to try to estimate the misalignment of the teeth. I think it could be only a quarter tooth out and if so undo the sprocket again and flip it over before reattaching it. Check the set up again with the chain and confirm that neither crank or cam (clearances equal)  has moved before putting the chain and sprocket back on.

Temporarily install pulley and rotate the engine twice until you get back to the position you marked originally as TDC and check rocking valve clearances. If correct put cover back on (see method for fitting chain tensioner) along with pulley and before bolting up recheck valve timing.

[nicrguy1966]

31 minutes ago, johny said:

If the valve timing is confirmed to be wrong have a think about how to adjust it before starting. Heres my thoughts:

Assuming the sprockets arent marked youre going to have to be careful to keep everything aligned. I would turn (always normal direction of rotation) the engine to TDC and measure the clearances on valves 1 and 2 (having previously set them to 40thou). Then very carefully remove the pulley and cover and, checking you still have the same valve clearances, mark the positions of both sprockets relative to the backplate.

Next is the delicate bit as the crank musnt move while you undo the cam sprocket and remove it along with the chain. Once thats removed, temporarily put the sprocket back on in the same position and use it to turn the cam to its rocking position as indicated by equal valve clearances - again mark its position relative to the backplate. Use the loose chain pulled tight on the right hand side of the sprockets to try to estimate the misalignment of the teeth. I think it could be only a quarter tooth out and if so undo the sprocket again and flip it over before reattaching it. Check the set up again with the chain and confirm that neither crank or cam (clearances equal)  has moved before putting the chain and sprocket back on.

Temporarily install pulley and rotate the engine twice until you get back to the position you marked originally as TDC and check rocking valve clearances. If correct put cover back on (see method for fitting chain tensioner) along with pulley and before bolting up recheck valve timing.

Thanks. That all makes a lot of sense. I was hoping to have another play with the car today, but my fingers haven't recovered from 2 hours of pulling the fan belt to turn the engine on Saturday yet (see photo). I have labelled all my spark plug leads so that next time I do a final check that the cam timing is off, I don't (stupidly) think I'm saving time by not removing the spark plugs.

[johny]

Proudly wear your Triumph wounds😁

[Steve P]

I use a ratchet spanner on the alternator pulley to turn it over without plugs in.

S

[nicrguy1966]

3 hours ago, Steve P said:

I use a ratchet spanner on the alternator pulley to turn it over without plugs in.

S

Great tip, I'll give that try.

[nicrguy1966]

The skin has grown back on my finger and I repeated the whole procedure again, this time taking all the sparkplugs out first!

1) TDC market on the crankshaft pulley appears to be in the correct place (feeling the piston position through #1 sparkplug hole.

2) After widening the gaps on valves 1 & 2 as per the workshop manual, the gaps are definitely not equal at TDC.

3) The part I missed last time, the "balance point" where the gaps on valves 1 & 2 are equal seems to be 6 degrees after TDC.

What have I learnt:

1) It doesn't save time to try doing any work on the engine without removing the sparkplugs. Without the sparkplugs it was far easier to make fine adjustments to the crank position (and I kept the skin on all my fingers).

2) Sadly, I can't turn the engine using the nut on the end of the alternator, the pulley turned, but the fan belt didn't.

3) It's possible that my camshaft has been 6 degrees out for the last 15 years (when a reconditioned engine was fitted), and somehow my ignition needs to be way out in the opposite direction for the engine to run smoothly.

So, I ask the combined triumph hive mind, does a camshaft set 6 degrees After TDC make sense to cause the engine to need ignition set to 20ish degrees Before TDC to run smoothly?

Thanks in advance.

[Pete Lewis]

yes .  no, yes , er   no,   it will be fine,  no it wont ,  

the  answer is  reset the cam sprocket   reset the timing then tell us  !!!

a worn chain will make the cam late but not as much as 6deg  maybe get a chain as a standby

you understand the sprocket holes are indexed so you can get something like 1/4 tooth increments by swapping bolt holes  and you can turn the thing over and 

get more .

 

Pete

 

[johny]

Difficult one to answer definitively but how does this sound: the inlet valve is late closing so some compression of the mixture is lost. A less compressed mixture needs more time to burn so the timing has to be advanced or power is lost because the burn wont be complete until too far after the piston has passed TDC.

This is just a thought but it certainly seems quite possible...

[nicrguy1966]

38 minutes ago, Pete Lewis said:

yes .  no, yes , er   no,   it will be fine,  no it wont ,  

the  answer is  reset the cam sprocket   reset the timing then tell us  !!!

a worn chain will make the cam late but not as much as 6deg  maybe get a chain as a standby

you understand the sprocket holes are indexed so you can get something like 1/4 tooth increments by swapping bolt holes  and you can turn the thing over and 

get more .

 

Pete

 

I've read about how to adjust the cam timing, but I've never done it (or even removed the timing chain cover).

Any idea how much of a tooth 6 degrees is?

[johny]

well as I say by my calculations its about a quarter tooth and you can read in the manual how to achieve this. Just take your time and check and recheck before running but as our engines arent 'interference' design a valve can never hit a piston no matter how wrong the set up is👍 You can even take pictures at each stage for checking on here...

[Ian Foster]

On 02/09/2023 at 13:10, nicrguy1966 said:

Sadly, I can't turn the engine using the nut on the end of the alternator, the pulley turned, but the fan belt didn't.

When I had a standard mechanical fan, I used to use it when turning the engine to check/adjust the tappets. (you might want to wear a glove to protect your hands as the fan blades are quite sharp). Alternatively you could try tightening the fan belt so you can use the alternator pulley as previously suggested. 

Now that I have just and electric fan, I use a spanner on the crank bolt.

Edited September 5, 2023 by Ian Foster
spelling

[Pete Lewis]

1 hour ago, nicrguy1966 said:

Any idea how much of a tooth 6 degrees is?

i make it 42 teeth so thats 8.57deg per tooth so yours is around 3/4 of a tooth out so may need the sprocket turning over and much playing and cursing 

every time the chain falls off   

Pete

[RedRooster]

1 hour ago, johny said:

well as I say by my calculations its about a quarter tooth and you can read in the manual how to achieve this. Just take your time and check and recheck before running but as our engines arent 'interference' design a valve can never hit a piston no matter how wrong the set up is👍 You can even take pictures at each stage for checking on here...

It's a GT6 MK3, domed pistons, it is an interference design. When mine went bang it needed a new block. 

RR

[nicrguy1966]

23 minutes ago, RedRooster said:

It's a GT6 MK3, domed pistons, it is an interference design. When mine went bang it needed a new block. 

RR

Good to know! This is making me think it might be time to give a professional a chance to look at it. Luckily, a neighbour has recommended a 72 year old mechanic that's "seen it all before" and likes playing with classics.

[nicrguy1966]

36 minutes ago, Pete Lewis said:

i make it 42 teeth so thats 8.57deg per tooth so yours is around 3/4 of a tooth out so may need the sprocket turning over and much playing and cursing 

every time the chain falls off   

Pete

Another reason it might be time to let a professional mechanic do the work!

[johny]

48 minutes ago, Pete Lewis said:

i make it 42 teeth so thats 8.57deg per tooth so yours is around 3/4 of a tooth out so may need the sprocket turning over and much playing and cursing 

Hmmm I make it 21 teeth on the crank sprocket so each tooth represents approx 17º so if the crank needs to advance at least 6 degrees its got to be half a tooth which equates 2:1 on the cam to a quarter tooth. Have I got that right?

 

[RedRooster]

38 minutes ago, nicrguy1966 said:

Good to know! This is making me think it might be time to give a professional a chance to look at it. Luckily, a neighbour has recommended a 72 year old mechanic that's "seen it all before" and likes playing with classics.

It's because they changed the head to a TR6 one, so domed pistons to bring the CR back up. 

David Vessey is your man for engines, did a good job on mine. 

https://www.vessey-classic-car-services.co.uk/

[nicrguy1966]

2 minutes ago, RedRooster said:

It's because they changed the head to a TR6 one, so domed pistons to bring the CR back up. 

David Vessey is your man for engines, did a good job on mine. 

https://www.vessey-classic-car-services.co.uk/

I didn't think I had domed pistons, but I've not taken the head off to look (not since I owned a Herald anyway).

[johny]

Dont think all mk3 GT6 had domed pistons only from engine number KE10001...

[nicrguy1966]

4 minutes ago, johny said:

Dont think all mk3 GT6 had domed pistons only from engine number KE10001...

My car has a reconditioned engine (probably when the cam timing was messed up) and the engine number isn't readable (sadly).

[johny]

And you dont think you have enough knowledge now to correct the problem? Not rocket science although you dont want to rush it...