This is gonna be long winded, I'm new to big block Fords so bear with me...... I'm getting this noise, like a wrench tapping the block (almost like a diesel sound) I can hear it the loudest in the bellhousing and it starts within a minute of a cold start and does it at idle and any other engine speed. I had a buddy (Mopar guy) go for a ride with me and he swears it's "spark knock", he says you can hear it in the bellhousing because it's transfering from the crank and the bellhousing is like an amplifier. Now I've heard it ping under load sometimes like my dad's old Grand Marquis used to do 30 years ago, but this is a totally different noise besides that. My buddy thinks I need to run cooler plugs and maybe retard the timing, it's at 10* right now and the vacuum advance is hooked up, the plugs are Motorcraft ASF 42C. Before anyone says it's the flexplate, I already checked that and its fine and all the bolts were tight. I'll list the specs on this engine for reference: 73 460, bored .030 over, rods & mains are .010 under, flat top pistons with valve reliefs, deck height milled to .009, D0VE heads, mild hyd. cam with roller rockers, straight up timing set, headers, Edelbrock 750 with Performer RPM manifold. I bought the truck with the engine rebuilt and the only thing I've done is swap out the big cam and lifters that the previous owner put in with the cam and lifters that were originally in it from the rebuild. Does anyone have any suggestions on what plugs to use or timing, or if this is really even the problem? This is driving me crazy, it has plenty of power but sounds like crap and I really don't want to grenade the engine when it only has about 10k miles on it. I'd appreaciate any suggestions.

 

sorry to say it still sounds like flexplate to me. How did you check it? just pull hte starter and look at it? That doesn't tell you if the flexplate to crank bolts are tight enough, it also doesn't tell you if it's cracked. You may have to pull the trans to properly check it.

 

If you have spark knock at idle the starter motor wouldn't want to turn the motor over, unless you are running manifold vacuum to the dist. instead of ported vacuum. Where is the hose to the vacuum can on the dist. hooked up to?

 

I would suspect a longer flexplate bolt.
The bolts for a flywheel (manual transmission) and for a flexplate look almost identical, but the ones for the flywheel are longer. If used on a flexplate, they will strike the casting ribbings on the backside of the block.

Look for metal shavings or powder in the bellhousing, on the back side of the block. If possible, look up to the back side of the crankshaft. The bolts should just barely protrude out the back of the flange. If one or more look buggered up, you have found the problem.

 

Well first, I pulled the tranny completely out of the truck. I also pulled the flexplate and it was perfect, the bolts are only about 3/4" long and they were fine too, I didn't notice any marks on the block or backplate either. This truck has always been an auto and if I remember right, the guy I bought it from said the engine that's in it now came from a Lincoln, So I wouldn't think there would be a problem with the wrong bolts. When I pulled it every bolt and nut seemed tight and they are all torqued now, so that's why I eliminated the flexplate. I was thinking it could be the convertor but it looked good and was supposed to have been new when the trans was rebuilt 15k miles ago, if there was something loose in the convertor I wouldn't think it would last as long as it has. I pulled the trans pan and the oil was nice and bright red and there were no signs of abnormal wear. It's making the noise at idle but it's alot quieter, you almost have to lay under it with your head to the bellhousing to hear it. Also, the vacuum advance was hooked up to ported vacuum, but after I started this thread I tried running it disconnected and it does seem like it quieted down some. I'm going to go out today and play around with the timing a little and see if anything changes.......... Thanks for the replies.

 

You need to check to see if there is vacuum at the "ported " vacuum port when the engine is idling. If there is, the throttle plates are too far open at idle. This is a "tuning problem" and you will need to back of the idle stop screw to close the throttle valves and redo the mixture screws and you might need to bump the timing. How fast does the motor idle now?

 

I do agree with bear to check the vacum reading on the port you have the distributor connected to. There should be no vacum with the engine at idle. You could very well be pulling your vacum advance way too early which causes the spark to fire before the piston gets to the top. Check the total advance once you solve the knocking noise.

I'm going to go out on a limb here... Have you checked the engine running with a mechanics stethiscope? You may be able to find the source of the noise a little better. How long ago did you swap out the lifters and cam? I found out the hard way, wiped almost all my lobes, because I didn't remove the secondary valve springs while breaking the cam in. This gave me an unusual noise for a while, less then 15 miles, until I pulled the drain plug and intake to look at the cam. The next question is in reguards to the valve springs. Are they rated for the cam you installed? Meaning do they too high of spring pressures.

 

Yeah I never thought about the valve springs, that's worth checking into. I changed the cam about 6 weeks ago and have put about 300 miles on it, so I figured if anything was gonna happen with that it already would have. I changed the oil about a month ago and let it drain over a magnet and also cut open the filter and didn't see anything unusual. I know it's probably a no-no but the cam and lifters I put in were originally in the engine after the rebuild and had about 8000 miles on them, so I assumed that they were already broke in. The lifters were labeled (supposedly) for the spot they were each in and I used assembly lube when I put it together. I'll admit I don't really know alot about cams, but the specs I have for the one I took out are: duration .270 intake .278 exhaust, lift .480 intake .498 exhaust, this cam was really lopey and wouldn't idle very well under about 1200 rpm with pretty low vacuum. The one I put back in is: duration .260 intake .272 exhaust and lift .479 intake .504 exhaust, it's a lot more streetable with this cam, vacuum is about 17" at idle. I've had the idle set at about 650-700 and there was no vacuum at the ported outlet at idle. I went out today and set the timing back to 8* and with the vacuum advance disconnected all of the knock noise above idle have disappeared and it feels like it has more power. It still has that light rattley diesel noise at idle, so I'm thinking that is from something else. I've been trying to get ahold of a stethescope to track down the noises alittle better. I've done alot with cars, but mostly computer controlled FI engines in the last 15 years so I'm a little out of date with carbs and timing. I've been using 89 octane gas so I might try a tank of 92 and see if that makes any difference.