pnoland Posted April 30, 2016 Share Posted April 30, 2016 OK I have a modified l28 it has N42 head F54 block with flat top pistons and a .480 lift .280 duration cam. I get a rattle from the engine if I'm cruising at 80mph in 5th and I punch it, kinda sounds like someone shaking a pcv valve it will also do it stopped in natural if I give the throttle a quick hit as well as in other gears under the same conditions with different speeds. I have removed all adv. from timing I'm running 97 octaine fuel and I have installed new NGK B7ES plugs any help will be much appreciated thank you. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 30, 2016 Share Posted April 30, 2016 I have removed all adv. from timing How about a number? Are you running zero advance? Or is initial set to zero? Quote Link to comment Share on other sites More sharing options...
supernova_6969 Posted April 30, 2016 Share Posted April 30, 2016 hi! I had a mustang with an engine (that I rebuilt) that would make a rattling/ticking sound under certain circumstances. couldn't find it, and mechanics couldn't... one told me it sounded like it could be a bracket that I forgot to secure that vibrated only at a certain RPM/vibration combo. drove it like that for 2-3 years, never gave me issues. . not saying this is the case for you, but i'd check if everything is screwed in tight just in case.hope it's nothing. Quote Link to comment Share on other sites More sharing options...
pnoland Posted April 30, 2016 Author Share Posted April 30, 2016 I'm running 15* BTDC timing and as far as anything being loose it's not everything is tight iv gonna through and checked that already. Everyone I talk to says it's detonation. Quote Link to comment Share on other sites More sharing options...
TimZ Posted April 30, 2016 Share Posted April 30, 2016 I'm running 15* BTDC timing and as far as anything being loose it's not everything is tight iv gonna through and checked that already. Everyone I talk to says it's detonation. What fuel are you using? Octane? Quote Link to comment Share on other sites More sharing options...
pnoland Posted April 30, 2016 Author Share Posted April 30, 2016 What fuel are you using? Octane? I stated in the first post I'm running 97 octaine and have tried race gas. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 30, 2016 Share Posted April 30, 2016 (edited) I'm running 15* BTDC timing and as far as anything being loose it's not everything is tight iv gonna through and checked that already. Everyone I talk to says it's detonation. How fast does it advance from idle? Put the light on it and take a couple of simple measurements. Maybe you have a broken advance spring. Also, for troubleshooting purposes drop the timing to 5 degrees. Don't hold on to the number you want and try to make it work, Figure out what the real problem is first. 15 is already higher than spec. You have more advance than spec,, and a higher CR than spec. on an engine that likes to detonate. And, when did it start doing this? Are you familiar with the engine or is it new to you? Could be you're spinning your wheels on a bad tank of gas. Just because the pump says 97 doesn't mean it's 97. When you say you tried race gas, do you mean you drained the tank and refilled with "race gas" or just put a few gallons in? And, as I understand things, in certain parts of the country "race gas" means methanol. And they mix it with Mountain Dew and drink it, then go to the hospital. What's the octane rating of your race gas? Edited April 30, 2016 by NewZed Quote Link to comment Share on other sites More sharing options...
pnoland Posted April 30, 2016 Author Share Posted April 30, 2016 How fast does it advance from idle? Put the light on it and take a couple of simple measurements. Maybe you have a broken advance spring. Also, for troubleshooting purposes drop the timing to 5 degrees. Don't hold on to the number you want and try to make it work, Figure out what the real problem is first. 15 is already higher than spec. You have more advance than spec,, and a higher CR than spec. on an engine that likes to detonate. And, when did it start doing this? Are you familiar with the engine or is it new to you? Could be you're spinning your wheels on a bad tank of gas. Just because the pump says 97 doesn't mean it's 97. When you say you tried race gas, do you mean you drained the tank and refilled with "race gas" or just put a few gallons in? And, as I understand things, in certain parts of the country "race gas" means methanol. And they mix it with Mountain Dew and drink it, then go to the hospital. What's the octane rating of your race gas? As of right now adv. at idle is 15* at 5000 rpm it it 32* I am not running a vacuum adv as my vacuum diaphragm is torn as far as the race gas I went to the local track and filled my tank it is 110 octaine I am aware that I am running high CR but that's why I bought the motor I wanted a high compression N/A motor and it started just recently it seems I currently have the adv set at 10 every day I bump it back a few degrees and drive it to work and back to see if there is a change. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 30, 2016 Share Posted April 30, 2016 Why inch your way down from what is damaging your engine? Crank it way down to where it's gone and inch your way back up. If the head has been skimmed, you could have pretty high CR. But, the fact that it "started just recently" would indicate that the setup can work without detonation. More detail than "just recently" might offer clues. How long did it run well, what changes have you made recently, etc. Ideally, you would just dump as much information as you can in to a thread like this, in the first post. People will get bored and go away if it takes hours to just to get to the simple stuff. It took 10 hours just to find out what your timing was set to, and now 8 hours later, it's not even there, it's at 10. Good luck. Quote Link to comment Share on other sites More sharing options...
pnoland Posted April 30, 2016 Author Share Posted April 30, 2016 I apologize for my vague replies and lack of info as far as the adv goes I can set it at 15* retarded and it will still make the rattle and just recently is in the last two months maybe three it ran great when I put it in back in December I haven't done anything to the engine since January and I didn't notice the rattle then. I'm going to pull the valve cover and make sure nothing has come loose. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted May 1, 2016 Share Posted May 1, 2016 Check for slack in the timing chain. I have seen one engine that had a weird rattle similar to what you described. Turned out to be a busted keyway in the crank allowing the timing gear to slap back and forth. Quote Link to comment Share on other sites More sharing options...
pnoland Posted May 1, 2016 Author Share Posted May 1, 2016 Check for slack in the timing chain. I have seen one engine that had a weird rattle similar to what you described. Turned out to be a busted keyway in the crank allowing the timing gear to slap back and forth. Wouldn't the timing gear just spin freely if that happened. Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 1, 2016 Share Posted May 1, 2016 Kind of went thru a similar situation with a buddy and his fresh rebuilt L24. After the engine was warm it would rattle like detonation at around 2500-3000 rpm. We did every thing timing including a different dizzy. Tore the motor down for fear of damage. A different engine shop looked at and determined the bores were over honed and left too much piston clearance. The original engine shop tried to save original bore size and bones the sh!t out of it. I think it was like 6-8 thou over spec. Couldn't find any other reason for the sound. Engine is NOT back together yet. The bores looked like crap for what little miles it had on it. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted May 2, 2016 Share Posted May 2, 2016 Wouldn't the timing gear just spin freely if that happened. Nope. Not in this case. Quote Link to comment Share on other sites More sharing options...
acador Posted May 3, 2016 Share Posted May 3, 2016 I'd loosen the fan belt and see if there is any play in the water pump bearing. Rule out the low hanging fruit. Quote Link to comment Share on other sites More sharing options...
motorsci Posted May 3, 2016 Share Posted May 3, 2016 If you think its detonation get some copper tubing and a cheep stethoscope from harbor freight pound one end of the copper tube flat and drill a hole in it bolt it on the motor close to the head were the heater hose runs is good run the tube into the car and hook up the stethoscope hose to the tube if you here detonation you know its timing if you don't a least you wont be guessing there are electronic versions of this that I own but I still use this for tuning Quote Link to comment Share on other sites More sharing options...
pnoland Posted May 11, 2016 Author Share Posted May 11, 2016 OK after my 1979 distributor spun in two I found the rattle it was ignition adv front the worn out dizzy replaced it with a Kameari setup and boy what a difference thanks for all the help. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.