Hello everyone,

I'm not in the highest of spirits while I'm writing this thread. I've got a problem on my newly built 400 and I can't seem to find what's causing it. I've got a 400 bored .030 over, block has been decked, all side of the heads have been milled, Comp Cam with .494 lift, Comp True Race Roller chain. New valves, rockers, springs, etc. I stuck the engine in along with a new C6 about 2 weeks ago. Started the engine, set the timing and then spent the next 15-20 minutes adjusting and breaking the cam in. The next day I got exhaust on it and took it out on the highway. Round trip was no more than 60 miles. I varied the speed starting at 45 and increasing and decreasing every 5 miles. I decided to put some more highway miles on it and set out on a 100 mile round trip. I got half through it and developed a loud knocking noise. Immediately shut it down and trailered it home. Since then, it's been setting in my driveway. I recheck the carb and found out that my metering rods were .005 to large making it way to lean. Fixed that and the reset my time to 35# total timing. This still didn't solve the problem. I just got some 112 octane racing fuel hoping this will stop the knock. I checked all of the springs, rockers, pushrods, and lifters - no problems there. No corners where cut in building this engine. It's really pissing my off though.

HELP
Thanks,
Chris

 

Is this a bottom end or top end knock. Also what rpms is it knocking at.

 

I can't tell to be exact on the location of the knock. If I had to guess, I would say that it would be a bottom end knock. Only because it's a low deep knock. I've take a screw driver and listen to the top and bottom but can't locate it. The knock starts around 1000-1100, gets bad around 1500, and then either goes way or is drounded out.

Chris

 

I also ran a compression test and all but two cylinders where at 125 lbs and the other 2 were at 120 lbs.

 

How was the oil pressure and did it vary before or after it started knocking.

 

[updated:LAST EDITED ON 18-Jun-02 AT 07:08 PM (EST)]It has high oil pressure on start up and then once warmed up it lessens but, still in the normal range. I have notice that the pressure does vary while driving, not a great amount though. It has never been low or extremely high. It does not vary during knocking.

Chris

 

I would pull the pan it is better safe than sorry. It kinda sounds like a spun bearing. Is there a chance during assembly oil got under the bearings. Also you may check for a collasped lifter. I wish I had more insight to offer. Good luck

 

[updated:LAST EDITED ON 18-Jun-02 AT 09:47 PM (EST)]I would also check you disrbuter there is a bushing on the bottom of it. It will make bad a sound out of it. All it takes is to pull the cap and if the rotor pulls up with a lot of play than that bushing is bad.

 

Drop the pan and check number 4 and 7 rod bearings, if any bearings spun I'd look at those two.

 

Thanks for the advice,

I did as my engine builder said and ran some 112 octane through it to see if that wouldn't clear up the problem - NOPE! My engine builder finally came over to listen and it was decided that pan needs to come off and check the bearings.

Question #2: If my floats were set between a 1/16th to an 1/8th to high and I put 100 miles on the engine in this condition. Assuming that I'm at the same time washing some fuel past the rings, are bearing that prone to damage. I can't fathum that in this little of time, I've already spun bearings.

 

Um. did you change the oil after the initial run? Also is there any chance it could be an accessory before you tear it apart? PS pump, alternator?

Bear Tracks

 

I just changed the oil last night and it was pretty watery, smelled like gas also. It's not an accessory item. I'm full of disbelief that a bearing could go out at 100 miles when we've all seen the moron that doesn't do any maintenance and runs his engine at 7,000 grand all day but still doesn't spin a bearing. But, this is my first HiPo engine and my experience is limited in this area. So who knows what could happen.

Chris

 

I feel your pain. Been there, done that, bought the "T" shirt. I think most mechanics would tell you to do an oil change after the first 20 minute break in because of all the breakin materials, initial metal wear particles and the procees really distroys the oil. If your going to do a bearing I would do all the crank and rods.

Good Luck,
Bear Tracks

 

Would you describe the knock as a 'tick' or 'clickety-clack', a 'rattle', or a hollow metallic knock? Does it knock if you accelerate under load, or can you get it to knock if you rev the engine and then take the load off? The former would probably indicate a main bearing, the latter a rod bearing. Did you have the rods rebuilt? When you take it apart, carefully loosen the bearing nuts and bolts with a torque wrench set to the proper torque. While not definitive, if you find one rod or main bearing that loosens easier than the others, it probably was not torqued correctly during assembly, which is probably the most likely cause, other than defective bearings or problems at the machine shop. Did the builder plasti-gauge all of the bearings during assembly? Good luck!

 

Also, did you prime the oil pump before first starting the engine until you had positive oil pressure at the gauge?