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I wanted to check timing , the car runs fine but very nervous under 2000 rpm. ( for a short drive i could do recently )
I see 41° advance at 1000/1500 rpm without vac connected , i borrowed my brothers timing light , the same result.
I borrowed a prof timing light from a friend, rally cars garage , yep, 41°.
Very strange that it starts without pushing back with that much advance.
Ok, it's a Merlin 540 , so maybe it likes max 38° instead of the normal 36 ° due the bore being bigger. But at that low rpm ?
Will check tomorrow if the pointer/balancer is really TDC ... has a ATI Superdamper and a "aftermarket" pointer. Who says that those are accurate ?
A car "as bought" can have surprizes...
The first thing I would do is to look under the distributor rotor to make sure the centrifugal weight springs are there and that the weights move smoothly and with some spring resistance.
Then I would manually turn the engine to #1 TDC and see where the timing pointer is. There are a number of ways to do that--I usually pull the spark plug and use a screwdriver to determine when the piston stops moving up as someone else slowly turns the engine with a breaker bar.
Yeah, 41 deg at 1500 is too high. All in centrifugal advance should be at 2500 or more, but 2500 is good. 38 is probably a better limit than 41. Depends on the heads. Fast burn modern chambers can sometimes use less max timing, say 32 degrees. The motor will "tell" you what's good for initial timing. Some motors like 16 to 20 degrees static timing.
Check your distributor to be sure the centrifugal advance moves freely under a gentle hand twist, and retracts fully when you release it.
I have a distributor in the 68RS that has 40 degrees of mechanical advance built into the football and weight plate from the factory. If I remember right, it came out of a 275hp 327 for a manual transmission and the initial timing was 2 degrees after TDC (not before TDC as most are. I get a little worried about people telling others to set the initial up to 12 degrees before TDC and slap in soft springs when the OP doesn't know what is built into the distributor from the factory. It becomes a recipe for disaster with detonation.
Your 41 degrees could well be one of these distributors that someone slapped the soft springs in without knowing what they had. The mechanical advance is stamped on the bottom of the weight plate (e.g., 540 or 740 or 530 or etc.) The last two numbers are the mechanical advance from the factory. Also, if the bushing is missing on the pin of the football, that increases the mechanical advance even more.
Just a warning.
i first checked pointer with a TIG rod in #1 .. not accurate but seems OK.
Then i looked at the weights/springs , all is there , but... quite a bit oil at the bottom of the distributor , electronics grease dirty ( somebody was in there ) , the 8 contacts a bit burned in.
As i bought months ago a new HEI distributor ( Dragon Fire ) to carry as spare for our planned long trips , i just switched them. The springs in the new one are "stronger" , but can't measure that nor do i have a color code.
I have now a red cap instead of a black cap , perhaps my engine likes it more
Difference remark : in the old one , the boss for tach is welded in , while the new one is one piece cast/machined. Don't see any brand markings on old one.
Now testing... the same . Engine won't idle with less then 40 ° advance , at least that is what i see . I must say the timing lights ( i tryed 3 ) don't work very well , they shoot not regular. Perhaps there is de "fault"
Plug wire to thick ? No strong sparks ?? ( checked and i do have full voltage at the distributor ) .
same time i plugged in my AFR gauge , that seems OK , poor at idle ( 15..16 ) , a bit gas direct 13...14 , higher rev's 12...13 . But that is not under load of course.
no problem R66 , it was/is indeed a HEI distributor. I do really find those quite interesting , just one wire connection , it is +12V. Good design , a 8 point trigger wheel for each spark.
Of course to big for those that want to keep the ignition shields.
Maybe a silly question, but you do have the timing light sensor on the number 1 spark plug wire and not the number 2 or another one, right?
You described your issue as the engine running "nervous" below 2000 rpm. Can you provide a little more insight into what the problem is with the engine's performance?
Sounds like the first is GM HEI from the 70s and 80s. Is the coil in the cap? It must be either a C3 distributor or and aftermarket.
So you changed to the aftermarket distributor, cap, and rotor and it still runs the same way. I would retrace the wires to the plugs and verify the firing order on the cap. I know you are knowledgeable, but sometimes it happens. Also as Duck 916 suggested, assure you are on number one. Vacuum hose plugged.
I have had a bad new plug, but that doesn't explain the 40 degrees.
i double checked the wires , all is fine. I do measure on #1 , on the short part before the plug that is not shielded.
Wires were numbered on the distributor caps by PO , here you see them on the new one.
I assume that 2006 540 Merlin has the same firing order as a Chevy , it was wired as such.
the old one , which is hand engraved at the bottom with : #45884 and 24°@3000
I was a bit surprized to see the tach boss welded in ...
Maybe a silly question, but you do have the timing light sensor on the number 1 spark plug wire and not the number 2 or another one, right?
You described your issue as the engine running "nervous" below 2000 rpm. Can you provide a little more insight into what the problem is with the engine's performance?
it didn't idle well below +/- 1200 rpm.
Also driving ( the short trip i did with it so far ) i felt it to be not happy below 2000 rpm. According Massevette's post in 2006 there is a aluminium flywheel in it , could be the reason ?
And i didn't daire to test performance due the heavy steering , which is now solved i hope with new PS pump and new hard line on the R&P.
Last edited by belgiumbarry; Apr 14, 2023 at 02:48 AM.
I am afraid you are beyond my basic knowledge. Two distributors, both giving the same results seems to indicate a problem other than the distributor. It seems the Merlin 540 firing order is indeed the same as the standard GM engine. SWCDuke posted a problem with orientation of the driven gear at the camshaft and orientation deviation for factory resulting in poor performance. I don't know how you would verify the correct clocking with aftermarket distributors. I assume both aftermarket distributors have the driven gear clocked the same as GM original design. The original distributors have a dimple on the gear that should align with the rotor tip, I don't know that your units will have the dimple.
Maybe he will pick up on this thread and have some resolution, or you might PM him.
Barry, I think I would question the timing chain installation being off a tooth or timing marks being out of sync with TDC on the pointer. Does the timing advance when the engine is reved up or does it stay at 41 degrees (427Hotrod asked). Is one of your timing lights a dial back type that allows checking of advance at different rpm’s? If so what total timing does it climb to. Have you posted the camshaft specs before or do you know what they are? With all those cubic inches it would take a pretty big cam to run as rough as that up to 2000 rpm’s unless installed out of time. With modern rollers they don’t usually go to those big duration numbers anymore since the faster ramps and lobe width provide the air/exhaust flow.
I would also cross the lightweight flywheel off the list for the same reason of all those cubic inches.
thanks , but one can clock such distributor at any position , as long as the rotor corresponds with timing. If #1 is good and firing order OK, everything follows as it should.
What i want to say , the visual distributor position doesn't say anything . Logic we place the vacuum canister at the pickup side and start from there.
The dimple pointing rotor tip at TDC is just a help , so that at least the engine can be started and timing can be done. And of course you need to have the wires on the cap as factory . That dimple will be #1 i suppose.
Barry, I think I would question the timing chain installation being off a tooth or timing marks being out of sync with TDC on the pointer. Does the timing advance when the engine is reved up or does it stay at 41 degrees (427Hotrod asked). Is one of your timing lights a dial back type that allows checking of advance at different rpm’s? If so what total timing does it climb to. Have you posted the camshaft specs before or do you know what they are? With all those cubic inches it would take a pretty big cam to run as rough as that up to 2000 rpm’s unless installed out of time. With modern rollers they don’t usually go to those big duration numbers anymore since the faster ramps and lobe width provide the air/exhaust flow.
I would also cross the lightweight flywheel off the list for the same reason of all those cubic inches.
I wanted to check that yesterday , as 427Hotrod asked , but we got the neighbors here complaining noise and smell..... omg.
As you know we bought a "small" house last year and sold our "big" one , in the same street .
Must say , the neighbor woman is very sick , terminal cancer.... so i want to respect that as far.... ?
We told them of course this is to time the engine and not representive for the future .
They already complained last year due renovation noise on the house ....that we even asked contractors to dim their radio's etc....
One thought here. Is there any chance your engine got one of those 4-7 cyl firing order swap cams. I don't know how to be sure but some big block guys do.
OK - I guess that noise was with your new quieter exhaust modification too? You may have to get some flexible pipe extensions and a couple big old Cadillac mufflers to temporarily stick on your exhaust outlets just to keep the neighbors happy.
I guess in the meantime you could always play around with getting the #1 cylinder to TDC with a feeler rod or something, at least as close as possible without pulling the timing chain cover. See how well it seems to correlate with the timing marks.
Timing ....
, i borrowed my brothers timing light , the same result. 
