Detonation?
Thread Starter
Intermediate
Joined: Dec 2005
Posts: 33
Likes: 1
From: Charlotte NC
Detonation?
Greetings! I just retimed my '78. I had timed it before but with the vacumn still on the dist. This time, I took the vacumn off the dist. and timed it. It runs well, but when I gun it, I hear something that sounds like a valve rattle. Cound it be the valves, or could it be detonation? Also, what would detonation sound like? Since I have hyperutetic pistons I guess det. could be a bad thing. Any ideas or suggestion? Thanks in advance and I find this forum an invaluable tool in helping me with my vette.
Steve
Steve
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
IMO pinging occurs most often under load. Can result from having too much advance, excessive carbon build up on the pistons and combustion chamber or using too low of an octane fuel. Another thing that sounds sort of like a ping can be a valve problem where a spring has broken, push rod bent or valve lash too loose.
Since this sounds like it has just started after timing, let's assume you're timing is too far advanced. Let us know how you timed the engine and how you checked it.
Since this sounds like it has just started after timing, let's assume you're timing is too far advanced. Let us know how you timed the engine and how you checked it.
Thread Starter
Intermediate
Joined: Dec 2005
Posts: 33
Likes: 1
From: Charlotte NC
detonation?
Marshrat99, thanks for your reply. I'll retard the timing just a bit and see how it does. It does make sense that I set it too high, since I was not getting the pinging before. I'll reset it tomorrow. Thanks again.
Thread Starter
Intermediate
Joined: Dec 2005
Posts: 33
Likes: 1
From: Charlotte NC
detonation?
Lars, thanks for your reply, Sorry I did'nt get back sooner. I'll show complete ignorance of my mechanical ability by saying I set it at 4 below the zero mark. I say ignorance because I'm thinking that would be 40 degress advanced rather than 4. Please let me know how wrong I am. This is where I had it set before, but with the vac attached. I unplugged the vac and sealed off the vac. and then set the timing. Thanks again for any comments or suggestions.
Drifting
Joined: May 2006
Posts: 1,425
Likes: 0
From: Seattle Wash.
ecpirate,
Your total timing should be at 36* between 2500 - 3000 rpm, with the vacuum advance disconnected. Don't worry too much about the initial timing. After you have that set, adjust your carbs idle mixture. That should help the car run better.
Your total timing should be at 36* between 2500 - 3000 rpm, with the vacuum advance disconnected. Don't worry too much about the initial timing. After you have that set, adjust your carbs idle mixture. That should help the car run better.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
ecpirate -
You need to accurately set your timing. To do this, you need a dial-back timing light, or you need to scribe and mark your harmonic balancer for a 36 degree mark. With this, you then need to set your total timing to 36 degrees, which should result in initial timing somewhere in the 8 to 18 degree range, depending on your distributor's advance curve. But you must set total timing to 36 using a dialback light or a properly degreed balancer. All timing, of course, is adjusted and set with vacuum advance disconnected.
You need to accurately set your timing. To do this, you need a dial-back timing light, or you need to scribe and mark your harmonic balancer for a 36 degree mark. With this, you then need to set your total timing to 36 degrees, which should result in initial timing somewhere in the 8 to 18 degree range, depending on your distributor's advance curve. But you must set total timing to 36 using a dialback light or a properly degreed balancer. All timing, of course, is adjusted and set with vacuum advance disconnected.
Thread Starter
Intermediate
Joined: Dec 2005
Posts: 33
Likes: 1
From: Charlotte NC
Detonation?
Lars, thanks again for the advise. I'll retime this week-end and go for 36 degrees. Also, thank you Marshrat99 and 427-390
Last edited by ecpirate; Dec 14, 2006 at 08:16 PM. Reason: to thank the respondees
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