Timing and GAV

[Gabalus]

Just for fun, we made some road tests on a four banger.
We had tried on it : a stock model A head and a 6.0 snyder's head, a model A distributor, a model B dist. and a model A with 30° max nu-rex automatic advance, some ignition advance timing, model B camshaft (was in the block when we bought it), model A and B carb on model A intake, also some work on seat valves, ports and valves, ...
We recorded that :
_ with a model B camshaft, a model A carb, 6.0 head and automatic advance (approx 7atdc to 23 degrees btdc on crankshaft) the engine start and idle perfectly but overheat when we ran. If we opened the GAV, the rpm droped.
_ We changed to 28 to 30 max degrees. It ran quieter but we didn't saw a very significant power increase. If we opened the GAV, it didn't ran well.
_ When I opened GAV (1/2 turn) and modified carb float level (up), I could increase crankshaft degrees to 40. Probably more. The engine seemd to be very strong from 1500 to 2200 rpm but, with more than 10° at idle, it made ping under 1500 rpm. At higher rpm it was noisy (loud).

Did anyone show the same effects of the GAV/gas level on a banger ?

 

[tbirdtbird]

let us know how you make out

 

[Gabalus]

Thank you for your answer, tbirdtbird.
I'm agree with you.

I just want to be much clear in some points :

_ We tried total advance of 23° before tdc (crankshaft) after we've read very interesting posts here.
That didin't work (overheating and probably less power than stock engine).
_ So we've tried approx. 28 to 30° of full advance. The engine run quieter and we've got a little bit more power. We heard just a few time some gas firing in the mufler when we used "engine brake" (downhill).
_ When we opened the GAV, the engine run smooth and didn't overheat if we used more than 37° of total advance. The engine was completely different. It was like the torque increased about 50% !
.At high rpm (2250 and over), the car ran great but we thought, with the loud noise, we didn't want to brake something.
.From 1500 to 2200 rpm, it was better than perfect !
.At low rpm (1300), it's not exactly pings that we heard but I'd prefered to drive in second gear in town ! When we used engine braking (downhill), at 1300 rpm, the car was shaked forward backward, like an old and big one-cylinder Lanz Bulldog or S.F.V. ! Too much torque ? For sure, too much advance at those rpm !
.At idle, the noise was ugly and frighten me a bit !

The last time, we run it with 28°... Perhaps 25-26° will be the best full advance timing ?

 

[Gabalus]

Sorry, I made a mistake (in the future, I'll need to read two times what I'll write !):
_ first try : 7 ATDC to 23 BTDC,
_ second one : TDC to 30 BTDC,
_ third one : 10 BTDC to 40 BTDC.

 

[ian Simpson]

If you rise the compression ratio far enough to cause pinging, either increase the octane value of the gas or retard the spark.

 

[Gabalus]

We drove it with 97 ron gas and 98 ron unleaded gas. With stock head, it ran greater with 97 gas than 98.

We really don't want to damage bearings but we want to understand what's going on with this engine.

We don't understand why/how you could increase timing so much when you open the gav and have a very very strong+smooth run (at >1500rpm) and engine overheats with less than 37° total advance.
IMHO, too much gas in the cylinder retards firing but doesn't increase HP.
Any idea ? We really want to understand.

And, also, why this engine ran badly and had overheated with 23° total advance ?

Thank you for your comments.

 

[Tom Wesenberg]

How are you figuring the number of degrees of timing?

I'm thinking the timing base line may be off, because the timing figures don't make sense for overheating.

 

[Gabalus]

_ In a first time with the timing pin ( 23, 30, 35 and 40°), a scale and the hypothesis of 30° total advance builded in Nurex automatic advance ( 7° ADTC, 0, 5° BTDC and 10° BDTC).
_ After these tests, we re-timed the dist. for 23° total advance with the paint on clutch (and flywheel case) we've done, head off (7° ADTC). Bad results. We closed GAV and tried to put one clic down the column lever. The engine ran better but was still "sluggish" and overheating in some case.
We didn't see any real change with another distributor and a model B carb.

 

[tbirdtbird]

This still doesn't tell us "the timing base line".
1. Does your rotor tip at TDC correspond to the pic that Tom W posts every so often?

2. Are the timing gears properly indexed to each other? We just had a guy on here whose timing gear was 5 teeth off the crank gear.

How does the motor run if you put it all back to stock configuration?

 

[Tom Wesenberg]

Here's the timing gear location, and how the rotor should be positioned when the timing pin drops into the cam gear.

 

[Gabalus]

Thank you for your ideas and pictures.

We didn't take off the front timing cover.

The rotor was positioned the same way you did when timing pin drops into the cam gear.
When the paint on the pressure plate was positionned right, we heard/saw the first unscrewed spark plug fired.

With model a carb, model A head and model B distributor, the engine ran great and didn't overheat if we put a lot of total advance. It was hard to start it : bendix and starter didn't like that !

 

[tbirdtbird]

"When the paint on the pressure plate was positionned right, we heard/saw the first unscrewed spark plug fired."

What exactly does this sentence mean? I think we have a language gap we are trying to fill.

Did this motor ever run properly? If so, what has been done to it since it began running badly

 

[Gabalus]

Sorry, we are french...

To benchmark we took localized TDC (painting on the flywheel case and clutch mecanism when piston is exactly on top) and the spark of the sparkplug.

When we bought this engine, it was rebuild (3 7/8 bore, model B camshaft, new valves, ...) but badly rebuild (rods not squared and pistons touching one side at TDC and the other at BDC, valve seats "not round",...).
Before removing it, we tried to make it ran.
We discovered facts that we have tried to bring to you : with 40 degrees total advance and, with GAV opened, it didn't overheat, it had lot of power and ran badly at low rpm.
My mechanic neighbour suggested me, like Tbirdtbird, timing gears are not properly indexed.