8BA timing
 

Engine is a 276" 8BA about 2500 miles. Heads surfaced and clearanced just to not touching the pistons w/no gasket. L100, hi-flow valves, TDC set with positive stop method, coincides with dot on pulley. I've been running the converted Chevy distributor at about 18 degrees in by 2000 rpm, and 4 degrees vacuum. Rochester 2GV on a bored Mercury manifold. The engine has always bucked, or surged, on deceleration below 1200 rpm. It has always started fluttering above 2500 rpm with no load but runs fine on the road at any RPM. That has always bothered me. Haven't heard any pinging, etc.

Today I was checking things and decided to decrease initial advance some, and the fluttering above 2500 was better, so I backed it off some more and the fluttering went away. Timing now all in at 12 degrees and about -6 degrees initial. It starts as soon as it turns and I wound it to 4500 today on the test run. The bucking on deceleration is gone. I haven't driven it enough to know if running temps are affected.

On top of all that, my rebuilt clutch from Fort Wayne Clutch was smooth when installed, but gradually began to chatter. Now all the chatter is gone.

Has anyone had an engine that wouldn't take any more than 12 degrees total timing? Should it start that quickly at -6 degrees? I was thinking I someway missed on the TDC mark, but it matches the dot. I'm stumped, I hope someone can explain what is going on.

Re: 8BA timing
 

Doesn't sound right. Is total timing actually 6 + 12 = 18?

Re: 8BA timing
 

Isn't the "bump" on the pulley 2° BTDC? I may be misunderstanding you, but it sounds like yours is TDC. IT's a minor point, but it may be an indicator of something else.

Re: 8BA timing
 

Also, how was TDC determined? Ok, dead stop (I reread OP!).

Re: 8BA timing
 

total timing is 12 (-6 + 18 mech adv). I need to get mech advance down to 10 degrees so I can have 2 degrees initial, I think.

Re: 8BA timing
 

Is your Chev distributor mech advance only or also with a vaccum advance unit. My 8BA is fitted with a Chev distributor along with a vaccum unit. Both can be adjusted courtesy of Charlie NY and it works well.
I understood the bump on the pulley was at 4 degrees BTDC.
Mine has around 8 degrees vacuum and 22 degrees full mech advance.
It runs well at this set up. Previously had too much total advance about 38 degrees and the fitting of mech adjustable advance stop and same at vacuum unit was able to reduce down to 28 to 30 degrees total.
Phil NZ

Re: 8BA timing
 

That was based on the assumption something is off on your readings based on how it is running. No idea what it might be, but would guess that the total advance is closer to what I was suggesting, but that is just a guess.

Re: 8BA timing
 

My experience with flatheads is they seem to run best at factory settings. Stock initial timing
And around 25 total all in.
I'm using a duel point Mallory with a Pertronics
Conversion. Eliminates dwell issues with the points, and it works great.

Re: 8BA timing
 

I use a SBC harmonic balancer, bored and broached to match the TDC timing mark. I use the positive stop method to find TDC. The timing I run is 20 all in by 2K and 8 degs of vacuum . I set the initial for easy starting. I think your TDC zero is off some what.

Re: 8BA timing
 

I appreciate your opinions. I can ignore the TDC mark and try to set it where it runs best. I can't depend on it pinging to tell me I have too much timing. Am I correct in setting the total (initial and mech adv, no vacuum) to where it doesn't miss while sitting still? Is missing under no load (at 2500+ rpm) an indication of too much timing, especially if it smooths out with less. And finally, Is 6 degrees AFTER tdc too low to crank and idle nicely? Answers from those of you with much experience can help me find a happy medium on timing. Thanks for sharing. OH yes, I do have vacuum advance, currently limited to 4 degrees but can adjust. Present TDC mark is just below the dot, where you would expect it to be.

Re: 8BA timing
 

I don't quite understand what -6 is referring to. Advanced means anything "before top dead center" or BTDC. Initial advance is close to TDC so the engine will start easily. If you set initial after top dead center or ATDC, it's going to run like crap and may not want to start at all. The timing dot, mark, or what ever you want to call it on an 8BA crank pulleys are 2* BTDC. One of my mentors in my early years told be to set the timing to where it just started to kick back then advance it again till it quits doing that. This is a general thing but I've found it works relatively well on just about any reciprocating engine large or small.

Re: 8BA timing
 

Actually all flatheads use a initial timing of 0 or TDC with some varitaion of 2-4 BTDC degrees max.

Distributor advance has been 16 to 22 degrees over the years. The engine usually likes these numbers no matter what mods have been done. The advance typically comes all in at 2000-2500 rpm.:D:eek:

Re: 8BA timing
 

Thanks all, Consensus is that it should take more than 12 degrees advance. I need to do some more verification of TDC mark. First I'm going to run a large tie wrap head through the spark plug hole and see how it matches my current mark.

Re: 8BA timing
 

Good idea. I've had several moved timing marks of on SBC's because of slipped balancers, but that can't happen on a flathead (at least with the original crank pulley).

Re: 8BA timing
 

All indications are that the timing marks are off for some reason. Are you using a dial-back timing light? These things can fool you! After you double check your TDC mark, try using a different timing light, if you haven't already.
If the initial timing is really 6 deg. ATDC, the engine will start easy and idle smoothly, but will be quite doggy.
If total timing is only 12 deg., it is apt to overheat at road speeds. If you start the fire late, it is still burning when the exhaust valve opens, so raw flame is going past the valve and down the port. If timing is right, the fire is done burning when the exhaust valve opens, so only hot exhaust gasses are flowing out.

Re: 8BA timing
 

I agree with the previous poster about "dial-back" timing lights. I have had two, and both were off; one to a significant degree.

Re: 8BA timing
 

This is an original '40 crankshaft pulley. When It was off the engine I measured the circumference, divided by 36 and got 10 degree increments, then marked and painted the pulley up to 30 degrees advance. I'm using that scale, not the dial-back feature. I have another timing light that I'll compare tomorrow. The engine runs fine on the road with the 18 degree BTDC total timing plus the 4 degree vacuum advance. No pinging, etc. The fact that it blubbers and misses above 2500 RPM with those settings sitting still that has me double checking and I have to bring it down to 12 degrees before it smooths out at those RPMs. It is down some on power at 12 degrees, but not "doggy". My primary concern is that I do not harm the engine, and if it misses sitting still, what is it doing under load although I don't detect a miss?

Also, the clutch that chatters at normal settings doesn't do it at 12 degree setting. Maybe that can be attributed to being down some on power, I don't know. I drove it yesterday for about 20 miles in 90 degree heat with with the temp staying where it does at 18 degrees advance. I appreciate all the comments and suggestions. With all your help, we will get to the bottom of it.

Re: 8BA timing
 

You might have a fuel delivery problem or a weak condenser too. AF meter can help with mixture checks. A 1940 pulley isn't like an 8BA. It likely was not marked since they didn't use timing lights on them. You definitely need to check the TDC mark you have on there. It will have to align on the 8BA pointer when it's at TDC on #1 cylinder.

Clutch chatter is something else entirely. I can't equate clutch chatter with engine performance unless the engine has major missing, low power, or something of that nature.

Re: 8BA timing
 

Assume you know the procedure for determining TDC. But to be sure, you rotate the engine one direction until it hits the stop and mark the pulley (using a fixed pointer). Then rotate the engine in the opposite direction until you hit the stop and again mark the pulley. TDC is halfway between the two marks. It is best to repeat the process several times to get consistent results. The same fixed pointer needs to remain in place for use in timing. On the 8ba the pointer is already on the front cover.

Re: 8BA timing
 

I don't know of any engine that has an initial advance located ATDC.