Legere Spec 2.4L pinging

[opelwasp]

OK here it is. I have a 1.9L to 2.4L conversion. Combo cam from OGTS and dished pistons. I am using a 75 EFI distributor with the Crane XR700 ignition.

I can't set the timing according to the manual because the machinist who drilled my flywheel for my S-10 clutch drilled right through the timing ball. So I have to do it by ear.

I have the timing set to the point I can drive around town and on the highway fine, but...

I can set it so it wont ping under hard acceleration, but it will miss and buck at about 105 mph and will not go any faster.

Or I can set it more advanced and I can acheave speeds much faster but it will ping terribly during hard acceleration.

What gives?

[First opel 1981]

Is your vacuum advance working correctly? It sounds like you might have a sticky one, or possibly your centrifugal advance could be gummed up.

[hrcollinsjr]

105 mph? Hmmm, what's the speed limit out there?

Have you checked to make sure your mechanical advance mechanism is working properly?

Harold

[wrench459]

I have the timing set to the point I can drive around town and on the highway fine, but...

I can set it so it wont ping under hard acceleration, but it will miss and buck at about 105 mph and will not go any faster.



What gives?

Fuel starvation comes to mind.

[RallyBob]

Three things should be attended to IMO, most of which others have already addressed.

1) Make a proper timing mark...guessing the timing is not the thing to do on any performance engine!

2) Recurve the distributor. A 1975 distributor has 25 degrees of advance. Set it at 5 degrees BTDC, and the total timing will be 30 degrees. With a small cam and 91 octane CA fuel, there's a narrow window for correct timing. I'd pull 5 degrees out of the mechanical advance, and set it at 10 degrees BTDC for starters. It would leave you at 30 degress total still, but a bit more initial advance to help it from a standstill. You may need to slow the curve down too, I'd start by increasing the spring pressure a bit.

3) If you don't have at least a 25 gph fuel pump and 3/8" fuel lines on a Weber 38 DGAS, then you are emptying the fuel bowl out most likely. STOP driving it fast until you cure the problem. You will melt a piston and destroy the engine!

The first time I starved an Opel of fuel at high rpms it bobbled for about 3 seconds, and in that brief time I melted the electrode off the #2 spark plug. It doesn't take long to do damage without fuel.

HTH,
Bob

[BMWonly]

I ran into a similar problem after beefing up my 71 low compression motor to close to 2.0 (1.9 bored 60 over), with flat top pistons, OGTS combo cam, and a 38 Weber, stock distributor, and Pertronix.
Even after tinkering with the timing, only higher octane fuel got rid of the pinging. Now I am running about 1/4 tank 108 race fuel, the rest 91 octane (which gets me to about 95), and my motor seems happy at any driving conditions.

Dieter

[Gumby]

I can't set the timing according to the manual because the machinist who drilled my flywheel for my S-10 clutch drilled right through the timing ball. So I have to do it by ear.

Put a dial indicator on the block and measure the actual top dead center of the piston (it's really easy). Mark your flywheel for future reference.

[baz]

and your front pulley and timing cover for easy setting

[opelwasp]

Put a dial indicator on the block and measure the actual top dead center of the piston (it's really easy). Mark your flywheel for future reference.

Uh...I really didn't feel like removing the head just to set a timing mark. I had the flywheel done after the engine was assembled.

[jeff denton]

You can use a valve as a piston stop to find TDC. Just be careful, and think about what you are doing.

[Gumby]

You can use a valve as a piston stop to find TDC. Just be careful, and think about what you are doing.

If you can get a indicator on it a cam lobe would be more accurate.

[oldopelguy]

If you can get a indicator on it a cam lobe would be more accurate.

By "think about it" I assumed he meant getting the piston very near the top of the cylinder, removing one rocker arm and valve spring, and letting the valve fall on top of the piston. Then by carefully measuring the valve stem extending out of the head as you move the piston you can use it as an indicator.

Alternately, with solid lifters, you could over tighten the rocker arm to get the valve partially open, and then mark the crank where the piston hits the valve (gently), back the crank around the other direction until the piston hits again (gently), and split the difference for where TDC must be.

[grslightng02]

105 mph? Hmmm, what's the speed limit out there?

Have you checked to make sure your mechanical advance mechanism is working properly?

Harold

Don't y'all forget CalifornayA is about 70% flat farmland. We have our of movie stars, palm trees, and beaches.... but we also have our share of redneck country roads.... Smokey and the Bandit territory.

And of course OpelWasp has his share of Buford T. Justice contacts, bein' non civilian and all !

[deaner]

If you can get a indicator on it a cam lobe would be more accurate.

You can use a spark plug to do this. I've taken and old plug clean out the center and replace with an extended bolt. (trial and error on the length) install it in #1 hole. Rotate the engine until it stops. make a mark on the front pulley or flywheel. rotate in other direction until it stops. mark it again, exact tdc is half the distance of your 2 marks.

[RallyBob]

You can use a spark plug to do this. I've taken and old plug clean out the center and replace with an extended bolt. (trial and error on the length) install it in #1 hole. Rotate the engine until it stops.

Note: Rotate engine slowly....

[RallyBob]

Three things should be attended to IMO, most of which others have already addressed.

1) Make a proper timing mark...guessing the timing is not the thing to do on any performance engine!

2) Recurve the distributor. A 1975 distributor has 25 degrees of advance. Set it at 5 degrees BTDC, and the total timing will be 30 degrees. With a small cam and 91 octane CA fuel, there's a narrow window for correct timing. I'd pull 5 degrees out of the mechanical advance, and set it at 10 degrees BTDC for starters. It would leave you at 30 degress total still, but a bit more initial advance to help it from a standstill. You may need to slow the curve down too, I'd start by increasing the spring pressure a bit.

3) If you don't have at least a 25 gph fuel pump and 3/8" fuel lines on a Weber 38 DGAS, then you are emptying the fuel bowl out most likely. STOP driving it fast until you cure the problem. You will melt a piston and destroy the engine!

Addendum to above:

4) Put in a bigger cam suitable for a 2.4. It will stop pinging. It will be much faster....

[opelwasp]

Addendum to above:

4) Put in a bigger cam suitable for a 2.4. It will stop pinging. It will be much faster....

Yah, I'll run that one by my funding manager.

I'll have to wait till the Geo is back up. The plan is to put the motor into the Manta so I can drive it to the Tacoma meet.

[opelwasp]

2) Recurve the distributor. A 1975 distributor has 25 degrees of advance. Set it at 5 degrees BTDC, and the total timing will be 30 degrees. With a small cam and 91 octane CA fuel, there's a narrow window for correct timing. I'd pull 5 degrees out of the mechanical advance, and set it at 10 degrees BTDC for starters. It would leave you at 30 degress total still, but a bit more initial advance to help it from a standstill. You may need to slow the curve down too, I'd start by increasing the spring pressure a bit.

Would using a different year vacuum advance distributor work?

[GTJIM]

Uh...I really didn't feel like removing the head just to set a timing mark. I had the flywheel done after the engine was assembled.

Do you 'feel' like rebuilding the entire motor after burning a hole in a piston OR wiping out a rod bearing ??

'Pinging' is just like swatting the tops of the pistons with a 7lb hammer - hard and often!

1) Do not drive it until the problem is resolved

2) Use the piston stop through a plug hole method of finding TDC

3) Re-curve distributor to Bob's specs

4) Ensure an adequate supply of fuel at high speed

5) You may need a longer duration cam or less compression to fully 'cure' the pinging.

Please - some of us have been there before - It is the mistake only made twice ... the first and last time!

A different Opel distributor has even more advance in it - WORSE!

[hrcollinsjr]

Would using a different year vacuum advance distributor work?

The vacuum advance distributors have way more advance than is needed. There is a chart somewhere, maybe in the tech. section, with the specs copied from Mitchell's Manuals for each distributor. It has them listed by years with identifying Bosch P/N's as the distributor may not match the year of the car or engine that it was originally installed in.

Harold