Lthistle

I am hearing a tappett sound when my 403 is under load. No sound on a cold start. No sound on gradual acceleration. When I press a little harder on the gas or go up a slight hill, I hear that tappet clicking sound. I have plugged both the EGR ports. I have installed new exhaust to head gaskets and had both exhaust manifolds planed for flattness. I have installed the preper donut gasket on the passenger side, and made sure the crossover is plugged. So I very much doubt that the sound is exhaust. The engine runs smooth with no miss, just that pesky ticking. I have had the valve cover off one side to check the valve rocker bridges, ok on that side. Only thing didn't do is check the other valve rocker bridges. I wonder. Anybody want to comment ?

maxi426

Typically the bridges on the two cylinders near the EGR valve are worn the most.

67OAI

Are you sure that you are not hearing mild detonation commonly called ignition ping?

Lthistle

Thanks 67OAI. I thought of ingition ping. Matter of fact, the timing tag is broken off my 403, and I time it with a timing light and a 'GOOD GUESS'. So one of the things I will check is the timing.

redoldsman

If you have a vacuum gauge, try timing it until you get the highest vacuum reading.

oldcutlass

How do you use a timing light without am indicator? Based on your description your timing is too far advanced, probably compounded by the vac adv.

Lthistle

Oldcutlass, As I said I used the light with a best guess at where the timing tab and marker should be. Lots of pics of the timing tab on line to follow. I hope you are right and it is just preignition, or detonation. Tomorrow I plan to check it out. Thanks.

Dynoking

To eliminate detonation as the source of the noise use a vacuum gauge as suggested by reoldsman. Retard the timing then slowly advance the distributor until you get the highest reading. Use a grease crayon and your timing light to make a reference mark on the front cover to mark where the crankshaft damper scribe lines up. Road test the car and back off (retard) the timing 2* at a time and see if the noise changes or goes away.
When you post a request for help please provide the year and model of the car, the year of the engine and any modifications that have been made. It will make it easier to provide help.

Lthistle

Thanks for your help dynoking. The car is a 1968 Chevelle Malibu, with a 403 Olds engine from a 1979 Trans Am. TH350 trans out of I don't know what. The engine is completely stock. The only modification is that I blocked the EGR ports on the intake manifold on both sides of the carb. I removed the exhaust crossover, plugged the crossover port and had true duel exhaust installed. The engine has about 50 thousand kilometers on it. I'll clean the distributor cap, install new plugs, and check my timing, and report back. Fingers crossed.

Dynoking

Kudos to you for the Olds into a Chevy swap. I knew I liked you. By clean the distributor cap I assume you mean remove the corrosion on the high voltage terminals located inside the cap? If so I don't recommend that. You may think you are doing the right thing. When you are finished the terminals are bright and shinny. That has to better than the crud that was on there before right? Maybe for a little while, but the corrosion (which comes from the high voltage arc that jumps off the tip of the rotor as it passes the terminals and is considered normal wear) will likely come back faster and may build up in greater amounts. This is because the scraping and cleaning process can cause the rotor/terminal air gap to increase raising the voltage needed to jump the gap and removes the protective coating that was applied during the manufacturing process. Some corrosion is ok and doesn't harm anything. If it gets to be too much the best practice is to replace the cap and rotor as a pair.
Please keep us apprised of your progress.
Best,
Richard

olds 307 and 403

Awesome on a 403 in a Chevelle 👍. Is it the stock low compression? If so, it should be able to tolerate a lot of timing. Try unhooking the vacuum advance and plugging it. If the sound goes away, it is timing related. It could be a stuck lifter. It could be worn bridges and rockers. Were they replaced on the rebuild?

Hammerdrop

When I changed the exhaust on my 307 the EGR did not function right because it relied on backpressure in the exhaust. Under part throttle, pinging was the result. Your EGR system strategy might be different, but the original factory tuning possibly relied on the EGR to suppress spark knock. By disabling the system, a problem was inadvertently created.......possibly.

Sugar Bear

X2 ^^^, If you are running 87 octane try 93, if the noise decreases or goes away it's detonation/pinging.

Lthistle

Thanks Hammerdrop. However, I covered the EGR ports a long time ago, and the tapping sound is fairly recent. I have to replace the home made gaskets regularily because they make a ticking exhaust sound too, when the gaskets wear out.

Lthistle

Thanks Olds307 403. I am not sure if it is the low compression engine. I did not know there was a different compression model out there. The engine was not rebuilt. I purchased it with 45 k kilometers on it. I am not getting a sound out of the valve train, even using a ratchet extension as a stethascope.

Lthistle

A little update. This morning I took off my distributor cap and (against advice) I cleaned the high voltage terminals. I tried sucking on the advance tube coming from the carb. Hmm no movement in the mechanism. I found a small leak in the hose. SO I figured A-Ha......Well I wasn't getting much advance out of that but that should not cause detonation. After fixing the vac hose, I went around the block and the ticking sound was exactly the same. Next I retarded the timing a bit. Since I have no timing tab or a vac guage, I moved the distributer only a couple of degrees. Around the block again. Thiis time I noticed a very slight difference in performance, maybe a tiny bit sluggish. BUT, that tapping noise is still the same. Folks, now I am back to thinking exhaust leak. My next move is to remove the drivers side manifold and install a new gasket, but first have a better look at the cylinder head/manifold ports. Sorry if you guys are getting 'ticked' off with my ameteur work here, but I am as they say only a back yard mechanic. By the way , the drivers side exhaust manifold is real hard to get at.....Steering column, alternator, brake booster, all in the way to some degree. That's one of the only drags with the 403 in my A body Chevelle. By the way, my car was a 6 banger with a 308 non posi rear end. I know that sounds odd, but It works out good and easy on gas.

redoldsman

Olds engines normally don't use a gasket between the head and the exhaust manifold. These are machined surfaces. If you pull the manifold check the manifold and the head with a straight edge to be sure they are flat with no warpage.

Lthistle

Thanks Redoldsman. I had both manifolds planed, and they are straight. I will check the head though. I knew they came from the factory without gaskets.

Lthistle

A quick update. I know it's been a while. Today I took off the passenger side valve cover. I took off all rocker pivots and rockers....no wear at all. I oiled 'em back up and installed. I also checked those oil drain holes at each end. There was a little junk in there but the oil cold still get by. Next move is to re-examine the driver side valve rockers and pivots. I did this a month ago, but I need to be sure. After that, I'l try some ATF (automatic trans fluid) in the oil. Some say about a cup full can free stuck lifters. Anyone want to comment on that ?

olds 307 and 403

You could try ATF or an actual oil flush. What weight of oil are you using? Really go through exhaust but usually exhaust leaks are more noticeable cold.

Lthistle

Thanks Olds307 403.......I am using 10w30 oil. I have worked every exhaust point up front, head to manifolds, pipe joins, EGR and choke ports. I had all the rockers and pivots off yesterday and found none worn. I am pretty sure it's valve lifter noise. I have heard about putting some ATF in for 100 km or so, then change oil. However I don't want to ruin my engine. That's why I asked about the trans fluid.

olds 307 and 403

You could run straight ATF for that mileage. GM engine flush used to be really good. A 20 year Ford tech, I apprenticed under swore by it. He eliminated a cold piston slap on his 2.9 V6 Ranger. I gained 5+ psi of oil pressure on a high mileage Olds 307 using it.

Greg Rogers

OK I have tried to get others to do this and no one seems to want to try it, but the easiest and best way to identify a noise on a running engine is this. Go to a auto parts store and buy 3-4 feet of 1/4" vacuum hose. Take off air cleaner and plug any lines, etc you have removed. Start engine, stick end of vacuum hose in your ear- not too far!! Now run hose around engine as it is idleing. You will tell when you have set end of tube near cause of noise. If noise is only when you load engine, then rev engine. I did this just a few weeks ago on my car and it ended up being the head to exhaust manifold. I have suggested this before on other threads and am ignored. It works really well, much better than using a stethoscope or a screwdriver. Good luck!

Lthistle

Hi Greg....and thatnks for responding. I have done a similar thing, by holding a ratchet extension bar on the engine and against my ear. I can hear many little
tick tick tick sounds, but nothing that I'd say 'found it' ! I will report back after I try the trans fluid additive trick.

Lthistle

PROBLEM FIXED ! No more ticking sound ! Thanks to 67OAI, oldcutlass, dynoking and olds 307 and 403. You guys suggested it might be engine ping, detonation, pre-ignition. You were right. This morning I unhooked the vac advance and plugged the carb port. I drove around the block and the tapping niose is GONE. Not a tick from the engine. I guess I had way too much timing and the vac advance made it worse. I guess I need to buy a timing tab and time the engine correctly.

olds 307 and 403

Super, a very easy fix!