Model A, Small block chevy, 350 trans. Under normal driving all is fine. Under a more aggressive acceleration just before its about to shift I hear a noise like something hitting a fan blade. The car has an elec fan. Any ideas? Thanks
How close is the fan to the pulleys? Could be a bad motor mount and the engine is raising up and hitting the blades. Just my humble opinion...kinda need more info or pics
Also check to be sure driveshaft isn't touching anywhere in tunnel, I had that happen under hard acceleration
funny you bring this up, i just put a 350 in a OT pickup, it's an egr engine with the egr unhooked, it drives fine, but when i stomp on it a cracking sound comes from the carb, if i pull the air cleaner off and run the throttle by hand it dam near sounds like someone in the engine shooting at me.
Detonation/spark knock? Like somebody has a tin can with loose nuts rattling around inside it? Try some octane boost & hightest gas, see if it goes away - or it might be because the timing is doing oddstuff under low vacuum, coupled with a heavy load it'll make spark knock.
Don't wanna scare you, but possibly a rod knock? You said, "just before it shifts." At this point, there's less of a load on the engine, and a slight rod knock might only be heard then. Hope not.
Your problem sounds like your advance in your distributor may be malfunctioning, or you are running on the edge of detonation...I may be wrong, but def sounds like something isn't quite right...
take a video with good sound, put it on youtube, and we can all go for a ride with you and figure it out.
I had a 64 Chevy that kept breaking distributor caps. One day I had a friend brake race it while I watched the engine and I was surprised to see how far up a sbc will raise on the drivers side when the motor mount is broken. The distributor was hitting the firewall and cracking the cap, but sometimes it would just raise up and slightly push the cap offsides and the car would miss and break up. You might want to try that. Don
Checked the converter bolts, all tight. Inside the inspection cover is all clean, no marks. Again this only happens when it is about to shift on aggresive acceleration, 1st to 2nd and 2nd to 3rd. Such an odd sound, for 3 seconds before it shifts, like baseball cards on bicycle spokes
cam lobe is rounded and exhaust valve is not opening far enough to allow the spent gases to flow out of the cylinder. They end up popping through the carb when the intake valve opens. or pre-ignition knock.
bopwop...just thinkin'...if cam lobes were rounded, wouldn't it sneeze out the carb at low rpms on acceleration? Easy enough to check that though...pull valve-covers...see if all the lifters are moving the same.
what is history/condition of engine? if there is a heavy carbon build up on pistons there can be a noise like you may be hearing. cure is to very slowly run automatic transmission fluid through carb with engine running.
Bought the car with the motor in it. Car was put together but not finished. Running when I got it. Has edelbrock cam, carb and intake matched set. Sounds pretty healthy otherwise. I just rewired the car to fix the hack wiring. redid the brake lines etc And just drove it for the first time besides a 1 mile test drive. I have to deal with exhaust this week as it touches the ladder bars. I figured once I get past that I need to dial in the noise. I do not believe the exhaust is causing the sound.
You didn't happen to stop at a different gas station than the one you usually go to by chance? Gas that isn't up to the engine's requirements is one thing that comes to mind when you get a noise like that. Unless you spent a lot of time at low rpm cruising speeds just before that happened I wouldn't think there would be a carbon problem as Jalopy Joker suggested. I use to "tune" my grandfathers car about every other month that way though. The engine would probably lift up with a broken mount at initial acceleration rather than just before it shifted. Loose Torque converter bolts normally cause a knock at idle that goes away when you put a load on them. I got the 350R that I ran in my 51 Merc free because of that one years ago. If making sure that the advance is right on the timing and good gas doesn't cure it I'd be thinking that I needed to take a serious look at the valve train. I just read Post #18, Fresh good premium gas or gas that was in the jug for the lawnmower in the car?
last time i had that noise, i found that was where the kids missing cat was at. the give away was finally the smell
I added 5 gallons at the station I usually go to. I will look at the timing next. I know the mounts are not broken, I am not running a hood currently while getting the bugs out so I would have noticed the cat issue immediately....lol
I believe I have found the problem. The starter gear is within .070 of the flexplate. I believe the process of the trans shifting puts pressure on the flexplate and it touches the starter gear. Going to get a new starter as I never could get that one to stop squealing when I started the motor Will let you know when I get the new starter and install it, thanks for all the suggestions
Don't bother with a new starter. Just put in a starter shim or two. A .060 feeler gauge between the block and the starter is a temporary fix. Chevy dealer might have the shim, if not just make one. Make sure you use the bracket/brace on the starter too. Yeah, the one everyone throws away because it's a bitch to install. You really do need it.
Its already got a cheap summit ministarter. So going to get a better starter. Its not a shim issue, the starter has to be redrilled and moved towars the front of the car. Its too close to the flywheel when the car is running not when starting
Changed the started and shimmed the new one towards the front of the car and the noise is gone. Thanks for all the input
2 cars of mine, both new builds made the same pinging like noise under acceleration. I showed them to all the experts and no one had a clue. For 5000 miles in one and about 1200 miles in the other these 2 SBC's sounded like they were ready to launch part$ all over town. In the end I shimed the starter cones away from the housings and repaired the dreadful noise. Ring gear was whippng against the starter drive gear on hard and light acceleration. Case closed!
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