Knock Knock

[steve from staten island]

I may have a issue and I'm trying to stay calm. I cant get the car to run right. I have carb issues and I'm waiting for a new choke as the old one hangs up. Ive tried adjusting the carb after its warm but it still wont idle good. My question is first about timing. I trued timing it to zero on the tab on timing case cover with vacuum advance plugged. It wont run right. then when i connect vacuum advance it advances so much that idle screw wont slow it down. So now i dont know were timing is as I've been doing it by ear
My question is i know to far advanced will make it knock under load but now when i rev it a little i hear what i think is a rod knock. Ive heard engine knocks before and this sounds the same. Granted my hearing sucks but its there. Don't hear it at idle and at steady rev i dont know, but when i goose it i hear it knock and dam it sounds like a rod.
The background is there is no millage on this motor and maybe only a few hours running time. The heads were done by a good auto machine shop. I bought a short block from a guy that was 30 over and crank was cut 10 thousands. Had new pistons, TRW replacement rods. The motor was dirty from laying for years, i took it apart cleaned everything and reassembled. it spun nice and the clearances were within tolerance. However I'm no engine builder. I was on more of a budget back then and i admit to making many mistakes with this car. Im really needing to hear what some of your opinions are about the timing versus the knock i hear.....Thanks

 

[moparnation74]

Sounds like a possible vacuum leak, relating to the idle issues...The key is it runs, not well but runs.....Go to the basics...

The "knock" is a complete separate issue and does not sound good....Sounds like a tear down...

A video would be helpful...when you get the idle issue resolved.

 

[747mopar]

You never time to zero, it should always be before top dead center.... maybe 12-30 BTDC depending on your combo. The knock however has me concerned, I've never heard a motor knock unless under load so......

 

[Skey]

You never time to zero, it should always be before top dead center.... maybe 12-30 BTDC depending on your combo. The knock however has me concerned, I've never heard a motor knock unless under load so......

I agree about not knocking due to timing issue unless under load although a wrist pin or rod knock will make noise without load. You can sometimes pull plug wires to find which rod or piston it is, be careful though they will bite you especially at higher rims.

 

[steve from staten island]

so.... if it looks like a knock walks like a knock quacks like a knock LOL. Yes it has me concerned. Thing is i didn't hear it till tonight. It wasn't there before id have heard it. This car will not beat me no matter how hard it tries

 

[beanhead]

Firstly you should have your vacuum advance disconnected and plugged, before making adjustments. That said, timing too retarded (0°)can cause a rough knocky idle, so try setting it at about 12° BTDC...if it improves things at all you can advance it a little more to the point the idle RPM just begins to level off. When that's set you can then adjust the carb idle mixture and speed. When you reconnect your vacuum advance, use the 'ported' or 'timed' vacuum port. (The one that doesn't suck until ypu give it throttle) It shouldn't be adding any vacuum advance at idle. See if it helps!

 

[PP1RT]

Try the old carb cleaner trick to find the vacuum leak like moparnation said. Might need to tighten down the intake or carb a little more since the motor has gone thru a few hot cold cycles now.

Before i ever had the funds for a timing light we just had someone sit in the driver seat and hold the brake while slipping the car in gear. Turn the distributor til it runs free and easy. Mark that spot then shut down the motor and try starting it. Turn the distributor til the engine cranks the easiest and mark it. Then go back to half way in between the two marks and fine tune from there by the seat of your pants.

 

[super-bee_ski]

I'm surely NOT an expert
We have MANY on the forum, seriously....we do.
BUT: I just had the same issue on one of my cars, a 68 Firebird.
I finally pulled the recently rebuilt Edelbrock off and took it to an old time Carb guy.
He said even before he looked at it: "Accelerator Pump"
I told him it cant be, just re-built.
He said they make 2 types, the ROBUST one withstands the NEW GAS being used for Fuel Injected CARB/CAFE gasoline.

It fixed my issue.
Just saying.

 

[Ski 61701]

So what brand of accelerator pump did he put in? Just curious I still have a couple of leather ones left. Just trying to figure things out for the future.

 

[moper]

If there is vacuum present at the vacuum advance line then the throttle is too far open. So I think go back to basics. Set the engine to TDC on compression. Remove distributor and verify the oil pump drive is in properly. Then reinstall the distributor, setting it to be a little before "0". Make sure the firing order is right. wire the choke wide open. Back out the idle speed screw until the throttle closes, then go back in about 1/2 turn past the point where the throttle starts to open again. Then try and start it. It should start and idle. You might need to keep the throttle open a little with the gas until it's a little warmed up. Then use a timing light to set the initial timing to 15* initial. Use the idle screw to drop the idle speed down to 750-800. Then use a vacuum gage to set the idle mixture screws to the highest smooth vacuum reading.

 

[steve from staten island]

Found the problem. Vacuum leak. Ran very well after that but will set timing as you described. I still hear a knock when i goose the throttle. Not as noticeable but its still there. I suspect a Rod/wrist pin. Im not going to do anything about it now except keep moving forward to finish the build. Maybe when its done i will do a short block 383, or maybe a stock 440

 

[moparnation74]

Found the problem. Vacuum leak. Ran very well after that but will set timing as you described. I still hear a knock when i goose the throttle. Not as noticeable but its still there. I suspect a Rod/wrist pin. Im not going to do anything about it now except keep moving forward to finish the build. Maybe when its done i will do a short block 383, or maybe a stock 440

I had no doubt it was a vacuum leak...........The knock is what it is.....

 

[steve from staten island]

I had no doubt it was a vacuum leak...........The knock is what it is.....

You called it correctly and thanks

 

[HEMI-ITIS]

Long shot,,,,,,on that knock. Make sure the converter bolts are tight. I had one get loose and back out enough to hit the block.I thought for sure it was a rod knock

 

[moper]

Like Al said - check the convertor bolts, and I'd stick a diagnostic quality mechanical oil pressure gage on it and see where things are. My truck's had a wrist pin noise for 10 years now. Sounds like hell but the oil pressure has never varied.

 

[HEMI-ITIS]

Also pull the dipstick.How does the oil look ,does it smell like gas??

 

[moparnation74]

Also pull the dipstick.How does the oil look ,does it smell like gas??

I so want to change your last word Hemi....lol.....

 

[steve from staten island]

Its running nice now. I had a bad vacuum leak. I reset the timing, adjusted the carb again and i dont hear that knock, so maybe it was related to the leak. Im relived and happy, thanks

 

[moparwacko]

Glad to hear you got it Steve. Is the vac advance working? And holding steady- not immediately leaking down? If so, some adjustments can be made on the advance with Allen screw.
Good luck