It the sixpot an interference engine?

[Roger]

15 minutes ago, johny said:

Look at drawing 57 which shows lobe 1 exhaust just about to open and lobe 2 inlet just closed

We interprete this drawing differently. To me it shows the position of the cam lobes (no 1 cylinder) when the exhaust is about to close and inlet is about to open. This happens at TDC at the end of exhaust stroke and the induction stroke begins. Not at TDC before power stroke (after compression).

Edited December 31, 2023 by Roger

[johny]

Drawing 57 is looking at the cam from the front of the car and shows lobe 1 with lobe 2 behind it. Lobe 1 is exhaust and is just about to lift the follower while lobe 2 the inlet has just lowered the other follower as the cam rotates clockwise👍

[Roger]

50 minutes ago, johny said:

Lobe 1 is exhaust and is just about to lift the follower while lobe 2 the inlet has just lowered the other follower as the cam rotates clockwise

I must be daft, but this do not make sense to me for two reasons:

1)     You mention that exhaust valve is just beginning to open. That does not happen with piston at TDC. The exhaust valve opens when the piston is at the bottom (BDC, or actually just before BDC) so that the piston can push out exhaust gases on its way up.

2)     The sequence of events does not make sense to me either. If the inlet has just been closed (inductions stroke just completed) then the piston is also at (or close at) BDC after just completing the induction stroke, and the piston has sucked petrol/air into the cylinder on its way down. The sequence of the strokes are induction-compression-power and exhaust, and I just cant see that happening in that order as you describe it.

Maybe some champagne will make me see the light, this is confusing… Thanks for your patience Johny.

[johny]

Dont forget that these drawings are only representative not actual. Also the lobes start to operate the followers well before the valve is fully open. From diagram 58 the inlet just closes at 58* after BDC and  exhaust starts to open at 58* before BDC. These figures are of course where the piston is not the position of the lobes...

[Roger]

2 hours ago, johny said:

Drawing 57 is looking at the cam from the front of the car and shows lobe 1 with lobe 2 behind it

Well, to add some confusion: Drawing 57 seems to be incorrect on page 1.126 in WSM (Alternative, it is a drawing that shows the camshaft looking from behind the car).

The pictures below shows the camshaft looking from the front of the car and the camshaft is here turned so that the point of balance is upwards. On the drawing it looks as lobe #1 (exhaust) is pointing to the left, but in reality it is lobe #2 (inlet) that points to the left. Hence, exhaust is about to be closed and inlet valve is about to open if the camshaft goes CW. Still not convinced.

Edited December 31, 2023 by Roger

[johny]

No I think youve got the cam upside down there Roger. Lobes 1 and 2 should pointing downwards as the drawing is only representative...

[Roger]

Ok, on the picture below I Have turned the camshaft 180 degrees. So if the exhaust is just about to open here, and the inlet is just about to close: Which stroke has just been completed, and which stroke begins at this point? Where is the poston at this point of balance?

[Steve P]

I think you are over thinking this, just time the cam to the correct setting with  a degree wheel and it should be fine.

S

[GrahamB]

To add my understanding, and perhaps more confusion.  With No1 at TDC and the rotor arm pointing away from No1 contact in the distributor cap, the exhaust valve is about to close and the inlet is staring to open.  With normal valve clearances, both valves will be very slightly open so no gaps between rocker and valve stem.  By opening the clearance up to 1 mm for both valves, although the rockers will have started to move, there will still be a measurable gap, which if the cam is timed correctly, will be exactly the same for both the inlet and exhaust valves.  If the gap to the inlet valve is smaller than the gap on the exhaust valve, the timing is advanced.

[johny]

32 minutes ago, Roger said:

Ok, on the picture below I Have turned the camshaft 180 degrees. So if the exhaust is just about to open here, and the inlet is just about to close: Which stroke has just been completed, and which stroke begins at this point? Where is the poston at this point of balance?

This is the position of the cam at TDC explosion. Its the only position on the cam where lobes 1 and 2 are both not operating valves. After this the cam will turn CW until lobe 1 starts to open the exhaust near BDC and then after BDC the second lobe will start to open inlet so its fully open after the next TDC (intake stroke). Dont forget half a turn of cam is one complete turn of crank...

[Roger]

13 minutes ago, GrahamB said:

With No1 at TDC and the rotor arm pointing away from No1 contact in the distributor cap, the exhaust valve is about to close and the inlet is staring to open.  With normal valve clearances, both valves will be very slightly open so no gaps between rocker and valve stem.  By opening the clearance up to 1 mm for both valves, although the rockers will have started to move, there will still be a measurable gap, which if the cam is timed correctly, will be exactly the same for both the inlet and exhaust valves

Thank you Graham, this was vey helpful and correlates with my interpretion of the WSM. I had to go to the garage and test your statement above and for me it seems to be correct when turing my engine. The only thing that does not seems to be correct is the fact that my inlet seems to open too early when doing this.

[johny]

1 hour ago, GrahamB said:

To add my understanding, and perhaps more confusion.  With No1 at TDC and the rotor arm pointing away from No1 contact in the distributor cap, the exhaust valve is about to close and the inlet is staring to open.

So the valve timing is done at TDC exhaust/intake (exhaust valve just closing)? I'll have another look at the manual...

[Roger]

1 hour ago, johny said:

Its the only position on the cam where lobes 1 and 2 are both not operating valves

Unless you increase rocker clearance to 1 mm, then none of the lobes will operating the valves even if you turn the cam 180 degrees. I think this is the point that creates confusion!

[Straightsix]

Here’s a piston stop I made from an old spark plug, which I copied from a YouTube clip. Worked fine. 👍🏻

Edited December 31, 2023 by Straightsix
Photo omitted?

[Roger]

45 minutes ago, Straightsix said:

Here’s a piston stop I made from an old spark plug

Thanks, I have to make one. The endoscope camera works fine as a "sanity check" to see if the mark is way out, but I will need one of those tools when I do the valve timing.

[johny]

1 hour ago, Roger said:

Unless you increase rocker clearance to 1 mm, then none of the lobes will operating the valves even if you turn the cam 180 degrees. I think this is the point that creates confusion!

Ive got to apologise Roger! Looking at the previous thread on this subject we agreed that the valve timing has to be done on exhaust TDC. The manual isnt very clear on this but of course it fits your findings much better as valve 2 inlet is just opening and valve 1 exhaust is just closing👍

[Roger]

25 minutes ago, johny said:

ve got to apologise Roger! Looking at the previous thread on this subject we agreed that the valve timing has to be done on exhaust TDC. The manual isnt very clear on this but of course it fits your findings much better as valve 2 inlet is just opening and valve 1 exhaust is just closing👍

No worries, I learned a lot about valve timing when cranking my engine by hand looking at the lobes, and I'm quite sure that my valve timing is not correct. It will be interesting to start the engine after re-adjusting the valve timing and see if I have found my missing horses!

Edited December 31, 2023 by Roger

[johny]

So your getting different measurements of clearances 1 and 2 when at TDC (exhaust😁) - what are the readings?

[Roger]

11 hours ago, johny said:

what are the readings?

None! The inlet valve opens way before the point of balance at exhaust TDC so there is no clearance to be measured. I would probably have to increase clearance from WSM 1 mm to 3 mm (or more) in order to be able to measure and define the difference which does not make sense. This is what made me so worried that I did something wrong.

Happy new year everyone!

[Roger]

12 hours ago, johny said:

The manual isnt very clear on this

I agree 100%! As Pete said "bit of Triumph daftizum". This is what Triumph engineers forgot to add in WSM on page 1.126 and 1.127:

1) Always turn engine and camshaft clock-wise (looking at engine from the front of the car) during the valve timing.
2) The point of balance is at TDC on the exhaust stroke.
3) The reason for opening up the clearance on rocker 1 & 2 to 1 mm is that these valves would otherwise be slightly open at the point of balance and there is no clearance to be measured. Hence, the balance / imbalance can not be measured with standard 0,25 mm clearance.
4) Drawing 57 on page 1.126 is incorrect. It shows the camshaft lobe 1 & 2 looking from behind the car.

It's of course %&¤# obvious now after cranking the engine 500 turns observing lobes, debating here, looking at (incorrect) drawings etc, but sometimes the information in WSM can be really misleading. We should write a new edition and include all missing info and correct all errors! Might be a new topic for the forum.

[johny]

Well done, yes doesnt look to be any doubt that youll be taking your chain and sprocket off - nice little job to start the new year. Im starting on memory therapy😂

[DanMi]

I use 2 dial gauges rather than measure the gap. So I would close the gap then zero the gauges with the exhaust and inlet fully closed. Then when no1 is at TDC at the end of the exhaust stroke the exhaust will be closing and the inlet opening but at TDC both gauges need to be at exactly the same lift the actual value does not matter. There is quite a bit of adjustment just by moving the sprocket on the cam as the holes are slightly larger than the bolts.

[Roger]

26 minutes ago, DanMi said:

I use 2 dial gauges rather than measure the gap

Thanks Dan, that is my plan. I already bought a second dial gauge a week ago. Doesn't have to be an expensive one since the actual value does not have to be accurate as you mention. I removed the cylinder head not long ago, I really regret not checking this then. Learning the hard way as usual...

[Pete Lewis]

yes remember anticlock will generate all the slack of the non drive side of the chain and put a big error in crank position

Pete

[Roger]

25 minutes ago, Pete Lewis said:

anticlock will generate all the slack of the non drive side of the chain and put a big error in crank position

Another thing that should have been mentioned in WSM on page 1.126!