What Degree of Timming Should I Use?- 4.2L w/ 4.0L - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 07-14-2003, 03:59 PM
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What Degree of Timming Should I Use?- 4.2L w/ 4.0L

Hello All,

Well I finally took out my CJ this weekend in order to begin "breaking in" the engine. It runs much better than before.

I have a '82 4.2L block, 4.0L head, Crane Cams H-260-2 camshaft, clifford intake, 390 cfm carb, and factory headers from a Cherokee.

My question: What should I set my timming to? Should I use 6-8 degrees BTDC?? I want to set "optimal" timming, if that exists.

I know how to set the timming, its just that since I have a "performance" cam, different intake, and carb I don't know if I should use the stock timming value. The engine has about 20 miles since I rebuilt the engine. Also, should I wait for the engine to "break-in" more until I set the timming? It's running fine right now, no pinging.

I've done a search for this question, but most timming posts are how to install the timming chain or set the distributor.

Please advise.
Thank you for your help.

Mike [img]images/graemlins/smile.gif[/img]
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post #2 of (permalink) Old 07-14-2003, 04:02 PM
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

1. Where's it set?
2. If it ain't broke,
3. Don't fix it.
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post #3 of (permalink) Old 07-14-2003, 04:08 PM
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

Well, I just set the timming by "ear." I moved the distributor until it was running smooth at idle. Should I just leave it as it is? Its running OK.

I'm just asking because of the cam I installed. I don't know if it has to be at a certain degree to get its "full potential" out.

Thanks for the reply.
Mike
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post #4 of (permalink) Old 07-14-2003, 04:16 PM
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

I seem to remember reading something once about setting timing on any engine. You need a tach and a vacuum gauge. Get the engine warm and prepare to set timing as usual. Plug the vacuum gauge into the distributor vacuum. Get the engine RPM's up (2000ish). The trick is to advance the timing to the point of greatest vacuum while keeping the RPM's about the same. You have to play with the accelerator, distributor to achieve this. You retard the timing 1 degree from where you get the most vacuum at this RPM and that is your "basic timing". Keep the vacuum advanced plugged and see how it performs - you want a slight ping. Adjust the timing until this is achieved and you have your timing for your new modified engine. Then plug the vacuum advance back in to the distributor.

Of course you need to tweak as per your needs. Hope this helps. Worked for me on an old 360 rebuild with a modified cam.

Scott
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post #5 of (permalink) Old 07-14-2003, 04:25 PM
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

Thanks, I'll give it a try.

Mike
post #6 of (permalink) Old 07-14-2003, 05:38 PM
 
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

advance the timing until it spark-knocks at low RPM under load (500-600 rpm going up hill trying to accelerate) and then back it off until it doesn't spark-knock.

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post #7 of (permalink) Old 07-15-2003, 02:53 AM
 
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Re: What Degree of Timming Should I Use?- 4.2L w/ 4.0L

This might help you Timing on the Cheap
HTH
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