Cam/Crank timing.

[olonas]

I'll sort some pictures.
I have found something very strange with the crank/cam timing.
With No 1 cyl. at t.d.c. on it's firing stroke, with both valves fully shut, checked clearances, rotor arm at No. 1 cylinder, the "dot" on the camshaft pulley is 180 degrees out.
With the two dots in line together, the rotor arm is at no. 4 cylinder and both those valves closed.
I have checked that the rotor drive is not 180 deg out by fitting another distributor.
The engine has run perfectly which would indicate that the valve timing and ignition timing is fine.
I wonder if the distributor drive gear has been fitted 180 deg out?
I fitted the sprockets and chain some years ago. I know they were fitted with the two dots correctly aligned. I can't remember where the keyways were when I did that. The crank keyway will have been at the top, but can't remember where the cam keyway was when the dots lined up correctly. I possibly didn't check whether it was at 1 o'clock!

[olonas]

timing marks rotor at 4 resize.jpg (100.06 KiB) Viewed 3337 times

cam keyway rotor at 4 resized.jpg (111.2 KiB) Viewed 3337 times

rotor at 4 resize.jpg (80.65 KiB) Viewed 3337 times

These pictures show the timing marks aligned and the rotor arm a no. 4 cylinder. The keyways are at the correct positions, it's just the angle of the picture.

[olonas]

timing marks rotor at 1 resize.jpg (97.16 KiB) Viewed 3336 times

crnk at 12 rotor at 4 resize.jpg (84.26 KiB) Viewed 3336 times

rotor at 1 resize.jpg (108.17 KiB) Viewed 3336 times

These show the timing marks with the rotor arm a no. 1 cyl.
Again the crank keyway is at the top. Camera angle again.
Ignore the middle picture it is one with the rotor at 4.

[Bill_qaz]

So are you saying that, forgetting the distributor, that when the timing marks are aligned the valves on number 1 front cylinder are not both closed?

[philthehill]

If the camshaft has been ground correctly and the dot/mark line up the problem lies elsewhere. I suspect that the distributer drive has been fitted incorrectly.

[Bill_qaz]

If the camshaft has been ground correctly and the dot/mark line up the problem lies elsewhere. I suspect that the distributer drive has been fitted incorrectly.

That's why I don't understand the op statement Phil
"With No 1 cyl. at t.d.c. on it's firing stroke, with both valves fully shut, checked clearances, rotor arm at No. 1 cylinder, the "dot" on the camshaft pulley is 180 degrees out"

[philthehill]

Setting the distributer is secondary to getting the dot/mark aligned.
Once the dot/mark are aligned the OP can then set the distributer drive as per the BMC workshop manual.

[olonas]

When the dots are in line, the crank key at the top and the cam key at 1 o'clock, the rotor arm is at no. 4 cyl. with both valves closed on no. 4 cyl.. (1st picture)
When no. 1 cylinder's valves are both closed and the rotor arm at no. 1 cyl., the dot on the cam sprocket is 180 deg. from the crank sprocket.(1st picture in the further post)
The engine has been running fine for years and after now fitting a new chain and sprockets with the dots aligned and no 4 cyl. at t.d.c. firing stroke it starts and runs as before.
I think, when I fitted the now removed chain etc., years ago, I lined up the dots, crank key at the top, cam key at 1 o'clock and with out moving anything, removed the existing parts and fitted the then new.
Refitting the distributor drive turned through 180 deg. will not work because no 1 cyl. will the be firing with no. 4 cyl. at t.d.c with both valves shut. The correlation between the crank and cam will still be the same.

I did find this.
https://www.youtube.com/watch?v=unlA7pNGUeU

Fast forward to 2 minutes 15 seconds in.

The Workshop Manual, in section AA, only states that the crank key is at the top, cam key at 1 o'clock and the dots together and in line. There's no mention of which cylinder is at t.d.c. firing stroke. i.e. no. 4, not no. 1.

[philthehill]

Forget about the distributer for the moment. Set the alignment marks correctly and then set the distributer drive and distributer as per the manual.
It does not matter regarding the 1 or 4 cylinders because of the position of the lobes on the camshaft remains constant.
You to me are getting too hung up on the distributer end of the process. There is a set sequence for setting up the camshaft sprockets and distributer and if you do not adhere to it the drive setting process will be out of kilter.

[olonas]

Thanks Phil. I am now thinking it's correct. I added a paragraph, re the B.M.C./B.L. workshop manual, to my last post. That must be a similar omission to the M.G. manual.
I, probably mistakenly, thought that with everything aligned, mechanical timing, no. 1 cyl. would be on it's firing sroke. e.g. my first picture. It must be no. 4, as I discovered when removing the distributor cap.
That is contrary to distributor/ignition timing which is set up on no. 1 cyl. firing stroke.

[Bill_qaz]

So the valve timing marks are set with no 4 on its firing stroke. Is this on all A series Phil or just the minor?

[philthehill]

Bill
With the gears aligned as per the manual No: 4 exhaust valve is just starting to open with the inlet valve of No: 4 cylinder just starting to close. The exhaust valve of No: 1 cylinder is just starting to close and the inlet valve of No: 1 cylinder is just starting to open on its induction stroke.
The crank will have to turn 360 degrees to come to TDC on compression stroke so the timing (distributer rotor arm position) is still set on No: 1 cylinder.
It has to be remembered that the camshaft rotates 180 degrees whilst the crankshaft at the same time rotates 360 degrees.
Phil

[Bill_qaz]

Sorry Phil I don't follow,
if timing marks aligned, with crank key at 12 o'clock 1 and 4 are at tdc how can both cylinders have valves on the rock? as one of them must be starting its power stroke so both valves would be closed..
So my question was are timing marks aligned as cylinder 4 is at tdc commencing power stroke ?

[philthehill]

Bill
If the crank/cam marks are aligned the position of the cam lobes are as stated above.
The timing marks and the cam setting marks are two different kettles of fish.
I actually got a camshaft out and checked the position of the lobes against the position of the alignment marks and the above is what I found/determined.
Phil

[Bill_qaz]

So when timing marks aligned are neither 1 or 4 at tdc?

The crank key at 12 o'clock looks to correspond with tdc of the journals.

Screenshot_20240709-232010_Google.jpg (37.17 KiB) Viewed 3120 times

This would make one on tdc compression stroke and the other one on tdc exhaust stroke.
I understand valve overlap on exhaust stroke but wouldn't both valves be fully closed at tdc compression stroke?

[philthehill]

Bill
When the timing marks are aligned and the crankshaft key is at 12:00 and the camshaft key is at 13:00 both No: 1 & No 4 crankshaft journals are at TDC but not both journals are at TDC for the ignition/power stroke.
I can only tell you what I physically find.
Following the BMC wksp manual ref alignment of the crank and camshaft gears and the fitment of the distributer drive it all works as it should.
Both inlet and exhaust valves should be closed when the piston has passed BDC and the piston rises on the compression stroke.
Phil

[Jim McCrae]

Pistons 1 and 4 are both at TDC at the same time but one is at the start of its ignition/power stroke while the other is at the start of its induction stroke. Normally the sprockets are aligned with the dots together and cyl. 1 on its ignition stroke.

If the timing gears are set with the dot on the cam sprocket at the top rather than adjacent to the crank sprocket then the cam will be 180 out and cyl. 4 will be be on its ignition stroke and cyl. 1 on it's induction stroke. This is, I think what the original poster had reported.

If the distributor drive is installed appropriately, the engine will still run normally. The ignition timing marks will be out but I assume that timing can be set with a strobe on the lead for cyl. 4.

As the car is running normally, I don't think it is necessary to change but if the owner wants it to be "correct" by the book then he can realign the sprockets, re-install the distributor drive and reset the ignition timing.

I hope this makes sense and helps clarify things.

Good luck
Jim

[Bill_qaz]

Bill
When the timing marks are aligned and the crankshaft key is at 12:00 and the camshaft key is at 13:00 both No: 1 & No 4 crankshaft journals are at TDC but not both journals are at TDC for the ignition/power stroke.
I can only tell you what I physically find.
Following the BMC wksp manual ref alignment of the crank and camshaft gears and the fitment of the distributer drive it all works as it should.
Both inlet and exhaust valves should be closed when the piston has passed BDC and the piston rises on the compression stroke.
Phil

So that's is what I am saying Phil with the timing gears aligned number 1 and 4 are at tdc.
The OP states at this point number 4 valves are both closed.
So number 4 must be the cylinder at the top of its compression stroke .
So this would be described as an engine valve timed on number 4.
I am not questioning distributor timing which is using number one cylinder
All my original question was, has the 1098 engine and other A series variants always valve timed on number four tdc compression stroke?

[philthehill]

Bill
I have no idea! I just set everything as per the manual and it works.
Phil

[Bill_qaz]