Setting the Ignition timing - BTDC and all that jazz

[WorldClassAccident]

I am trying to get the timing about right before I fire the engine. Right enough to fire without grenading itself at least.

On other Scimitar threads I have seen talk about the W timing marks showing 10 and 14 degrees and also the fact that TDC isn't marked. The first photo's are from another thread describing the timing marks, the last is from my engine.





The picture of my engine is slightly skewed, the TDC mark I have drawn on the pulley and the block are vertically aligned and central to the car.

A - looks like it might be the snapped off remains of the timing W
1-4 are all notches cut into the pulley wheel. It is difficult to tell by looking what angle they might be but 3 is the biggest.

Am I right in thinking that if I point the TDC mark on the pulley at the (broken) timing W and the dizzy rotor arm at the lead for plug 1 I am approximately at 10-14 BTDC?

On some of the YouTube clips the blokes have been starting their engines and then twisting the dizzy a bit to adjust the timing 'until it sounds good'. I guess this is not best practice but would work to a certain extent. If you have any other suggestions for setting the timing please let me know. I am currently just looking to make sure the engine will run after being idle since 1989, not give it the final road tune. I appreciate tuning it properly will be necessay but I have a few other tasks to complete before that point

[Nike55]

Sorry can't help specifically.


(The missing timing block 'W', the corrugations of which line up appropriately with a single mark on the pulley, seems to be another 'sleeping policeman' on the road to your finished build.

You'll know from the threads on the 'other site' that lunching of pistons is highly possible and not being a Scim 'guru' I would suggest if no responses here then a quick plea via the RSSOC (if not done already) to find someone who can either talk you through it or suggest a member who might be able to visit or supply the no. of a local mechanic to you with 'Essex' sympathies to help out.

I guess you could try to find a timing block 'W' and a pulley with a single notch which may ease the sorting of any future timing issues).

Best wishes.

[WorldClassAccident]

Thanks. Just want to see if I can get the engine to fire. Not worried about getting it tuned to perfection.

I am planning on tracking down a friend or friend of friend who knows what they are doing.

Will check my 'spare' engine for notches and Ws

[donnysoutherner]

Am I right in thinking that if I point the TDC mark on the pulley at the (broken) timing W and the dizzy rotor arm at the lead for plug 1 I am approximately at 10-14 BTDC?

no reason why this would be true. if the engine is at TDC as shown, then I would put a mark on the timing chain cover corresponding to the big groove on the pulley. then get a protractor and make a cardboard template on a relevant sized circle for Approx 12 degrees as a starter. Then make a mark next to the other one to show 12 deg. Line the groove up with the new mark and you are at 12 deg btdc. Make sure the mark is on the right side of the original otherwise it won't work!

Get a test bulb and connect between the lead and the plug on 1 to set? When bulb comes on you are there. Worth investing in a strobe from eBay to set accurately once running.

Can you the turn and make it sound right method, but only when running and only if you have a decent ear for it. Bit like tuning twin carbs by ear, which I can't do.

[WorldClassAccident]

ds - makes sense. Just some clarification.

Make sure the mark is on the right side of the original otherwise it won't work! - when you say 'the right side' do you mean anti clockwise from the groove which in the picture is the left side?

Get a test bulb and connect between the lead and the plug on 1 to set - I have been using the buzzer on my multimeter which I guess has the same effect

Worth investing in a strobe - I am thinking of doing this but not sure I would know how to use it. On the 'How to' videos they point the light at the pulley wheel of a small block Chevy and there is a strip of numbers that they read from to get the number of degrees.

On my engine I guess I would have to put that strip of numbers onto the pulley wheel. I assume I would use the protractor method you describe to come up with these numbers but surely the number I see lit up will depend on where I point the light at the pulley wheel. Is there some magic position that I have to stand and a special angle I point the strobe?

[andrewhush]

Useful tool and method for accurately positioning the engine at TDC in this link.

http://www.pembleton.co.uk/ePAG/ePAG30/MGtiming.html

Ignore reference to cylinder 2, this info came from a moto guzzi site (90 degree v twin).

If you measure the distance around your pulley circumference you should be able to work out the number of degrees they are apart and be able to decide which one is TDC (0 degrees) and which is 6, 8, 10, etc. My guess is that no.3 is the TDC one and that 2 and 1 are two out of the 6 to 14 series.

My scimitar handbook lists 10 BTDC as the static setting (or running at slow idle with vacuum pipe disconnected) for 97 octane petrol but you may need to retard the ignition to cope with 95 unleaded.

[Nike55]

Excellent advice, duly bookmarked by me.

I shall now exit - stage left, saddened that I missed mrtowed's comment.

[WorldClassAccident]

Blimey, just had an expected date for the shell. Not next weekend which is good as I am hosting the Big Bike Bash but the weekend after.

Given that I am spending this afternoon decorating the bedroom, tomorrow family and cycling commitments, next week working and preparing for the BBB, the following week clearing up and recovering from the BBB this gives me this morning to fire up the Scimi.

I am off down the garage. Look out for blue smoke over Southampton

[donnysoutherner]

Originally Posted by WorldClassAccident

ds - makes sense. Just some clarification.

Make sure the mark is on the right side of the original otherwise it won't work! - when you say 'the right side' do you mean anti clockwise from the groove which in the picture is the left side?

Get a test bulb and connect between the lead and the plug on 1 to set - I have been using the buzzer on my multimeter which I guess has the same effect

Worth investing in a strobe - I am thinking of doing this but not sure I would know how to use it. On the 'How to' videos they point the light at the pulley wheel of a small block Chevy and there is a strip of numbers that they read from to get the number of degrees.

On my engine I guess I would have to put that strip of numbers onto the pulley wheel. I assume I would use the protractor method you describe to come up with these numbers but surely the number I see lit up will depend on where I point the light at the pulley wheel. Is there some magic position that I have to stand and a special angle I point the strobe?

Yep, buzzer will do same job.

Strobe works only when car is running. When connected at cyl 1 as per buzzer, will 'freeze' the mark on the pulley, allowing dizzy to be turned while running to align marks more accurately than can be done when not running.

when I siad 'right side' above, I meant as in 'correct'. Can put he timing numbers on either the wheel or the pulley, provided they count in the correct direction! On pulley, numbers would go clockwise for BTDC, on cover, numbers would go anti clock for BTDC.

Hope this makes sense, if not give me a call on 017810055920 and I'll talk you through it. Not that I've got mine going yet!

[WorldClassAccident]

All makes sense now thanks. I have even bought a strobe which should help once running. Useful already to confirm there is a spark in all plugs except 4 and then proving when I had fixed that.

Chickened out of adding petrol as wife wanted the bedroon decorating