engine knock

[scottyg118]

I'm afraid I'm probably not going to like the answer here, but here's the situation. MY '72 started to knock pretty bad today. I havn't had it long so I don't know much about these cars yet(or any for that matter). Anyway there is something making a lot of noise. I think it is coming from inside the block. I pulled the rocker cover off and noticed that the end of the tube that carries oil was broken loose on the end closest to the firewall and not supplying oil properly (ie. not letting it drip down on the valves.) Sorry I dont know what this is called but it is on the passenger side of the engine at the top. Am I screwed or what???

Thanx for the reply.

[2ManyZs]

The oil spray bar for the cam probably isn't causing a "knock", but it may have contributed to causing the knock. You will need to do two things.

First find out what kind of oil pressure the engine is carrying at idle and when you rev it up to about 2,000rpm. If the stock oil pressure gauge can't give you a good reading, by a cheap mechanical gauge at the auto parts store and hook it up to get an accurate reading.

Second, you need to find out where the "knock" is coming from. Is it down low in the block? Or does it sound like it is coming from the top of the engine in the head area. If you have a very long screwdriver, place it against the block and put your ear near the handle of it, it will act as a "stethascope" and you should be able to tell if it is high or low. If it is down low you may have a rod or main bearing about to go, if it is up high you may have a valve problem due to the spray bar being broken. Normally, if the spray bar just breaks apart, instead of spraying oil directly on the cam it will flood the head with oil. However, it may have caused a drop in oil pressure and caused a rod or main bearing to seize or spin.

Either way, it would not be a good idea to drive the car until you find the exact cause of the noise. Check it out and let us know and we'll try to go from there.

[jcdozier]

As 2ManyZs says, it's not a good idea to drive the car until you can track down the source of the knock. You may or may not be screwed now, but if you drive the car for any length of time, you will almost surely be screwed then. For instance, if the knock is due to a failing main bearing, if it fails under load you will be into big repairs.

Use the long-handled screwdriver "stethescope" trick to see if yo can localize the sound and post your findings. There's lots of good advice available from the folks here.

[scottyg118]

Well I am pretty sure the "knocking" is coming from the block. It's hard to tell because it sounds pretty much the same whether you listen at the head or at the block.

As for the oil pressure I got a pressure tester and it reads about 50 psi at 2000 rpm and about 30 psi at idle. My stock gauge reads about 45 and 65 respectively. I don't know what the exact specs are for oil pressure on this vehicle but these numbers seem reasonable to me. Where do I go from here??? I really appreciate you guys taking the time to help me out. Thanx again, Scott

[visionary]

If your oil psi is 30-45 then you have plenty of oil pressure in the engine. The oiler tube coming off will affect the cam lobes and possibly the rockers, valves and guides in the head. I have a '73 and have had problems with my oiler as well, however it was the front tube extention that has disconnected on mine. What I initially did was to have it brazed back to the cam journal mount but found that the braze didn't hold or seal well. I thought I would try some JP Weld instead and that has worked very well. You MUST remove the oiler from the cam journals first and thoroughly clean the entire oiler first. Then be very careful that you align the oiling holes correctly so they actually spill onto the cam lobes and don't allow the epoxy to clog an oiling hole. Mine were also clogged and I had to redrill the holes. If you do this be sure to rinse any metallic shavings that you may create before reintalling. My oiler looked like it had been made by a drunk production tech who was late for his tee time.

As far as the nonspecific knock coming from your engine. First, run some octaine boost, the best you can buy, then do a compression check on all cyclinders next and drain your oil and strain it to look for and metal or metalic shavings. Then report back to the forum for interpretation of the numbers.

[2ManyZs]

There are only a small number of things that could cause the knock, most aren't good. Bearings (either rod or main), piston to valve, wrist pin would be the most serious and costly. Your oil pressure sounds right which leads me to believe it may be piston to valve or possibly a wrist pin or rod problem. You really need to check it out thoroughly and soon before it gets any worse and is more costly to repair.

[scottyg118]

It sounds like this little problem may be more than I can handle unless I get real brave - real fast. Thanx for the advice so far. I havn't ever really done any major engine work. Where do you guys get your parts. I checked with NAPA and they don't have much for engine components. Thanx, Scott

[2ManyZs]

You can get the parts with no problem from MSA, VB and numerous other suppliers. The main thing that is needed now, is to find out exactly what is wrong. Sorry, but it may be one small thing, or it may be a major re-build.

Of course there is another alternative. If the engine is not the original or originality is not a concern to you, you could always just get a re-manufactured engine and just swap motors. If you have never done any major mechanical work you might end up spending as much to rebuild yours due to the labor costs as what a reman engine would cost to bolt in. MSA sells reman engines from ATK, so do some local parts stores. Or you can check out their web-site listed in the web-links here on the site.

[Phacade]

Resisting the temptation to turn the post topic into a bad pun (knock-knock joke). Like I said, a bad pun.

As far as a knock goes, depending on the severity of it I would park it and not drive it for awhile until it is fixed. Like 2MANYZS said; bearings rod or main, pistons issue or valve issues are usually to blame.

I have heard of another possibility. If you have an original L24, the rods used a 8mm bolt to secure them. Now in years past it was advised in old 70's hot rod magazines to replace pistons 1 and 6 at 100,000 miles. Not certain why and any guess I would make would be a guess at best. In any case I remember reading this in some old magazines of my Dads from when he had a '72 240Z auto when I was a kid. Alot of times the bolts on these rods were replaced with 9mm bolts as thy were bigger and generally more available. As a result the bolts themselves forced the bearings to wear unevenly and viola! Instant knock. Just a thought.

[918/240Z]

I'm still new to Zees myself but....

Is it a knock? or is it ticking? if you raise the idle a little does it get stronger knocking or faster ticking?

Have you checked your valve adjustments...... lets hope its the upper end (rockers from lack of oil) alot cheaper then getting into the block...

Any one out there that can help better describe valve noise?

can it be carbon build up .... detonation?? ( marbles in a can)

Just my 2 cts.

Good Luck Keep your Z alive Z ya Dave.