Chim ignition timing
Discussion
Can anyone help with advice on the timinmg marks. They dont seem to make sense to me.
Just had the distributor out replacing the vacuum advance and ensuring it worked smoothly, now trying to set the ignition timing but the marks on crankshaft pulley dont make sense to me.
I can see the big groove (I presume its TDC) and on the pulley I can see 'AFTER' written and a few very indistinct marks - but can see no marks at all 'BEFORE'.
Advance mechanism certainly moves the timing away from 'BEFORE' and it runs (idles) as good as expected when ignition set up on the big groove. If I advance to the 28-30 degrees BTDC it runs like a dog.
Is my assumption correct that the groove is showing TDC ??
Just had the distributor out replacing the vacuum advance and ensuring it worked smoothly, now trying to set the ignition timing but the marks on crankshaft pulley dont make sense to me.
I can see the big groove (I presume its TDC) and on the pulley I can see 'AFTER' written and a few very indistinct marks - but can see no marks at all 'BEFORE'.
Advance mechanism certainly moves the timing away from 'BEFORE' and it runs (idles) as good as expected when ignition set up on the big groove. If I advance to the 28-30 degrees BTDC it runs like a dog.
Is my assumption correct that the groove is showing TDC ??
Thanks - Im not far out, but why would the pulley have 'AFTER' stamped in it and no 'BEFORE' marks. Cant think of any reason you would need to be after TDC.
I think I'll have to establish if this groove is indeed TDC and then buy one of those timing lights where you can programme the angle.
I dont have a clock gauge that can do this so it will be an estimate but I remember on old 4 cyl engines you established TDC on #1 by looking at the rockers on #4, is there a similar check on the V8?
I think I'll have to establish if this groove is indeed TDC and then buy one of those timing lights where you can programme the angle.
I dont have a clock gauge that can do this so it will be an estimate but I remember on old 4 cyl engines you established TDC on #1 by looking at the rockers on #4, is there a similar check on the V8?
From memory the large notch isn't tdc so that's your issue probably.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Edited by Belle427 on Monday 4th March 18:44
Belle427 said:
From memory the large notch isn't tdc so that's your issue probably.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Ahhh, thats it! https://www.pistonheads.com/gassing/topic.asp?h=0&...
Edited by Belle427 on Monday 4th March 18:44
Perhaps a big assumption on my part that a groove in crankshaft pulley would be TDC. I only cleaned up the groove and either side of it - so never saw the other marks.
Many thanks - back on ot tomorrow
The groove is definitely not TDC, I believe it's a purchase point to rotate the crank?
The marks are exactly as Kris450 shows, but I wouldn't trust them on face value, especially if your engine hasn't been looked at/rebuilt etc.
Forgive me if you know this, but the crank pulley is in three parts, it has a harmonic balance which is a rubber connection between two sections.
I don't know exactly how it works, but am due to find out soon as I'll be checking my timing - a timing light shows it quite advanced, though the engine was rebuilt 7k miles ago including new crank and timing gear/chain, and there's no pinking sound that I've heard - which makes me suspicious that the crank pulley is out of position.
This thread picks up on the pulley, a post from Johnno has some nice clear images - good to understand what you're dealing with.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
But really, to Equus point, it's simple to check.
I am opting to make use of a friend's pit though, so I'm not trying to rotate the engine lying under it on axle stands (it's pretty difficult to get to the crank bolt from above).
That said, I found this video of a guy doing a few bits to his RV8 in an MGB, and he uses a chain wrench quite effectively to rotate the crank from above - access might be quite different on an MG though (from around 6.20" in the vid).
The marks are exactly as Kris450 shows, but I wouldn't trust them on face value, especially if your engine hasn't been looked at/rebuilt etc.
Forgive me if you know this, but the crank pulley is in three parts, it has a harmonic balance which is a rubber connection between two sections.
I don't know exactly how it works, but am due to find out soon as I'll be checking my timing - a timing light shows it quite advanced, though the engine was rebuilt 7k miles ago including new crank and timing gear/chain, and there's no pinking sound that I've heard - which makes me suspicious that the crank pulley is out of position.
This thread picks up on the pulley, a post from Johnno has some nice clear images - good to understand what you're dealing with.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
But really, to Equus point, it's simple to check.
I am opting to make use of a friend's pit though, so I'm not trying to rotate the engine lying under it on axle stands (it's pretty difficult to get to the crank bolt from above).
That said, I found this video of a guy doing a few bits to his RV8 in an MGB, and he uses a chain wrench quite effectively to rotate the crank from above - access might be quite different on an MG though (from around 6.20" in the vid).
What Pablo said. The damper is 2 steel parts bonded together with rubber. In this way the rubber can damp out vibration
However he did not explain fully that the bond of the rubber can fail and allow the outer ring of the damper (with the timing marks) to rotate with respect to the part bolted to the crank. So your timing marks are now in the wrong place. In my time working on TVRs I have seen 2 of these failures.
You need to make yourself a tool.
Take an old sparkplug, break out all of the ceramic and the central electrode. Drill out the centre and tap M8. Cut the head off an M8 bolt and screw it into the spark plug. You may need to experiment with the length.
Removing all the plugs will make life easier but not essential. Check that number 1 piston is not at TDC then fit the tool. Nice and carefully turn the engine clockwise until the piston stops against the tool. Mark the damper (Tipex) at the pointer. Now turn the engine anti- clock until the piston again stops against the tool. Mark the damper again. Remove the tool before you forget.
You can now measure between your 2 marks and TDC will be half way between.
If those marks are a long way apart measuring will be difficult so shorten the end of the tool and try again.
Steve
However he did not explain fully that the bond of the rubber can fail and allow the outer ring of the damper (with the timing marks) to rotate with respect to the part bolted to the crank. So your timing marks are now in the wrong place. In my time working on TVRs I have seen 2 of these failures.
You need to make yourself a tool.
Take an old sparkplug, break out all of the ceramic and the central electrode. Drill out the centre and tap M8. Cut the head off an M8 bolt and screw it into the spark plug. You may need to experiment with the length.
Removing all the plugs will make life easier but not essential. Check that number 1 piston is not at TDC then fit the tool. Nice and carefully turn the engine clockwise until the piston stops against the tool. Mark the damper (Tipex) at the pointer. Now turn the engine anti- clock until the piston again stops against the tool. Mark the damper again. Remove the tool before you forget.
You can now measure between your 2 marks and TDC will be half way between.
If those marks are a long way apart measuring will be difficult so shorten the end of the tool and try again.
Steve
Edited by Steve_D on Friday 8th March 17:23
Edited by Steve_D on Friday 8th March 17:23
That’s the most concise description of that exercise I’ve read to date. Thanks Steve!
Yes I neglected to mention that, though in my head I’d typed it!
Interesting that you’ve only seen two. Gives me hope that mine is in good shape, and I actually just need to adjust the timing, but will follow this method.
What method should be used to turn the crank?
Is it to use the central bolt (I bought a 15/16 socket), or better to use something link a chain wrench on the pulley itself?
Yes I neglected to mention that, though in my head I’d typed it!
Interesting that you’ve only seen two. Gives me hope that mine is in good shape, and I actually just need to adjust the timing, but will follow this method.
What method should be used to turn the crank?
Is it to use the central bolt (I bought a 15/16 socket), or better to use something link a chain wrench on the pulley itself?
The bolt is no issue to get an 1/2" drive bar or long ratchet on with a short extension a 24mm socket will work also even though the bolt is imperial A/F 15/16 , also just a heads up but if anyone's timing marked ring is creeping over the rubber insert (de-laminating) you had better change the pulley
Edited by Sardonicus on Tuesday 12th March 22:20
Sardonicus said:
............ if anyone's timing marked ring is creeping over the rubber insert (de-laminating) you had better change the pulley .....
Yes, if the damper has moved then the whole assembly must be replaced for 2 reasons:-- The whole thing could fall apart and most likely take the radiator with it on departure.
- The damper has had holes drilled in it during balancing of the crankshaft etc. so you cannot just fit another one (new or second hand).
Steve
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