Tweet
I've posted several messages regarding a "rapping noise" in a '66 big bock, 390HP. After having several knowledgeable mechanics listen to it, I was advised it wasn't in the valve train. (although one thought it might be a piston pin problem) I removed the engine today and have it on a stand with just the oil pan removed. I'm looking for suggestions on a sequence for trying to find the problem. I have not removed anything else from the engine, and I'm hoping if I can locate it as either a rod or main bearing I might be able to repair it without disturbing the upper end of the engine. I plan to start at the #4 cylinder, since the mechanics seem to think the noise was located there. I thought I'd unbolt the rod from the crank and inspect it. Any suggestions that might allow me to find the problem without any unnecessary dissmantling would be appreciated. The engine itself was rebuilt about 500 miles ago.
-
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
Rob,
I tried this approach a couple of months ago with the engine still in the car. Everything looked pretty good on the bottom end of my engine and it turned out to be a bad cam lobe. Did you find anything in the oil pan that would indicate unusual wear? -
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
John,
Actually, there are some metal filings in the pan. I suppose it might actually be quicker to just dissmantle the engine, rather than trying to slowly find the problem. I remember you telling me about your engine and the cam problem. Will it be obvious when I look at the cam if I have the same problem?Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
John,
When you found your problem to be the cam, did you leave the bottom end alone, and just replace the cam and lifters? (The engine runs fine, plugs very clean and burns no oil).Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
Rob - get a dial indicator and magnetic base, and measure the lobe lift of each lifter with lash removed. I like to do this with the lifter galley open with the intake off. You can also do it on the heads with the valve covers off, but at the stage you are at I would just do the former as it is easy to be more exact. you should quickly find if a lobe has gone away...CraigComment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
I would recommend following Craig's suggestion. It will be obvious if you measure properly. I would start in the area you suspect and work from there. It sounds like the cam is a likely culprit from what you have described. I would leave the bottom end alone until you rule out problems in the cam/lifter area. The metal pieces that you found lead me to believe that it is a cam/lifter related problem. Did the engine idle for long periods or in cold temperatures within that first 500 miles? I understand that cam failure as a result of improper oiling/excessive idling is not uncommon after big block rebuilds.Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
I actually like to break in the engine with the inner springs removed, to keep the pressure light, then after the 30-40 minute run in at no less than 200 rpm, I pull the valve springs and install. Also, make sure to use a high grade cam lube on the lobes at initial startup, with the lifter galley prelubed and the carburetor full of fuel without cranking to fill...CraigComment
-
Correction: 2000 rpm not 200, but typing is
at fault......CraigComment
-
Re: Correction: 2000 rpm not 200, but typing is
If you found metal in the pan,I'd cut open the oil filter and see what you find.
Its almost always the exhaust lobes that burn up,You could check them first.
But the hard parts done,(pulling it out again)
I would pull the intake instead,inspect each lifter for a dish,pits or flakeing.
Then pull the cam,looking for same,if a lobe or lobes are wore down the cam journals may be scratched and metal inbedded in the cam bearing and as well as rod and main bearings.Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
Well, the #8 intake cam lobe is all but worn away, and the associated lifter is not only worn so much that it curves inward(convex?) as opposed to having a slight radius outward(concave?) but is almost 1/8" shorter than the other lifters. I assume I have found THE problem, how exactly how does cause the rapping noise. By the way, good call John, thanks...Now I guess I have to figure out how this may have happened to prevent it from occuring again.Comment
-
If you found metal check the rod bearings and main
take it from experience you got it out this far you better check to make sure you get all the metal chunks out and flush your oil galleries no sense in puuting back together with a new cam and lifters and not checking the crank and everything else out and put a new oil pump in also just my 2 cents worth been there done that. DonComment
-
cam/lifter problems with BBC
always hone the lifter bore with a brake wheel cylinder hone to make sure they are smooth. the lifter should turn freely in the lifter bore so make sure you check this when installing lifters. alway polish the bottom of the lifters on 400/600 wet and dry paper using oil a lube. some lifter have a dark coating on the bottom,these do not need polished. the finish on some lifters is too agressive as sold. engine noise comes in 2 speeds,full engine speed it is rotating assy problems and 1/2 engine speed it is camshaft related. most cam/lifter problems come from the lifter not rotating. always set hyd lifters 1 at a time by installing the pushrods only as you set the lash because if you put all the pushrods in as you turn over the engine to set the lash you will collaps some lifers and when you set the lash on that valve you will be too tight causing the lifter not to turn.Comment
-
PS
make sure that there is a small champher(bevel) on the edge between the bottom and the side of the lifter. this edge should not be sharp. QC on these parts is not as good as it once was.Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
Your problem is identical to what I encounterd, Rob, and I hear it is not too uncommon. I ended up tearing the whole engine down for the reasons Craig mentioned. Clem indicates that cam preparation may be the best explanation for failure. Were they just trying to make me feel better about the work I had done when they told me it was a common oiling/idling problem at the machine shop? I had 2,000 miles and two years on my rebuild when the failure occurred.
I didn't want to take any chances the second time around and installed a roller cam and lifters togteher with a heavy duty oil pump. The cam and lifters were expensive but I believe that I picked up some additional horesepower and acceleration is much smoother. There are roller cams that are real close to original specs although the valve train will sound a little different after you install one. The heavy duty oil pump was under $50 and well worth the price.Comment
-
Re: '66 BB ENGINE RAPPING NOISE/ENGINE TEARDOWN
John,
As bad as the cam and lifter are damaged, I'm sure I found my problem. I'd like to confirm that this would cause the "rapping noise" I had before I stop looking for anything else that could have caused it.Comment
Comment