Hi I have installed a brand new crate engine in my 1957 Chev Pickup however it has a loud knock that makes it sound like a diesel at idle. Increasing the rpm to high idle makes the knock go away and advancing the static timing decreases the knock. Other than the knock, the engine starts and runs perfectly. All the usual stuff, like bearings, rod clearances etc have been checked. The engine was purchased as a 1996 to 2000 383ci Vortec Truck Engine and has 9.25:1 compression, roller camshaft and flat top hypereutetic pistons. Static timing is set for 10 deg. Instead of the fuel injection, we have carburetted the engine as it needs to run and be repairable in very harsh, out of the way places. Our best guess, at the moment, is piston slap. So, what are peoples guesses on what the knock is ? Can it, in any way, be caused by running a carb on a late model engine like this, that has a long stroke and short piston skirts ?
I don't know if the 383 sbc stroker has the same issues as my 331 Ford stroker, but mine is noisy as hell. When I first got it running I had 60 psi oil pressure but there was a rattle in the motor. Like yours, it got quieter with rpms. I tore the motor down, everything looked great, so I put it back together and it still made noise, so I called Scat and Keith Black pistons, and both companies told me the same thing..........some strokers are noisier than others due to the short pistons. When mine warms up it is a little quieter, but still sounds like a solid lifter cam. I have a bunch of miles on the car and it runs hard and has been no trouble, so I have just learned to live with the noise. Not saying that is your problem, but just maybe. Why don't you call the people you got the motor from and run it by them ? Don
Thanks for the replies guys. The engine supplier is ranting about it being a "fuel injection" engine and the engine has not been "designed" to run off a carb, therefore it is very hard for them to help. This reply seemed a bit weird to me and also to the professionals that I have had look at the issue here. The knock is really loud and occurring approximately once per revolution. It can't be isolated to a particular cylinder by removing spark plug leads. Mechanical fuel pump and rod have been removed. It is at its worst when it is warmed up. Sigh....maybe the joke is in this somewhere. Just haven't worked out the punch line.
Lots of info out there on the GM Cold Start Knock fiasco for their vortec engines. I bought a 1999 silberado new and had this problem. told all sorts of bull shit by techs, There were problem from 98-03 and seems related
Your intake (carb or efi) will make no difference on a bottom end knock. Any builder who says that it could be would go right to the top of my "this guy don't know what the fuck he's talking about" list. There's ways to diagnose a knock and to narrow its origin down. Knock knock ... Who's there ? ?
Have you pulled one spark plug wire off at a time to see if you can isolate it to one particular cylinder ? (Pull the wire off while the motor is off, otherwise you will light yourself up ) Don
I have an 03 Silverado with the 383 Vortec. It has had a "knock" since day one. It actually more resembles a lifter than anything else. I once thought I cold quiet it with a heavier oil than the required 5-30...It was WORSE...WAY worse. I have 65K on it now.
a quick google search for vortec knock will turn up a wealth of info. GM will, as in MANY other instances (gear noise in escalade front diffs, lifter noise in late models, etc.) pass it off as 'normal and acceptable'. most of what i've seen has to do with crummy machining tolerances. however, mostly not fatal. truth is, coming from a late model repair shop, it really is a live with it situation. another thing to consider is the way timing is set on these. you hafta remember that the timing is computer controlled in a factory vehicle. the base timing is set by aligning a mark on the distributor base with a mark on the block and the computer takes care of the rest as far as advance goes etc... from the factory, there is not even a timing mark on the balancer. not sure how that plays out on this particular engine, as i've never had this scenario in my shop, but it might be worth starting at 4* BTDC and working around to see if it makes a difference. timing issues aside, all the evidence points to piston slap. no recourse.
It is possible that the flex plate is loose,or cracked. A broom stick is a good way to isolate the noise. I would bet it's the flex plate.
Is the flex plate made for the one piece rear main seal crank? Almost positive their is a difference. Your crate motor may have come with the flex plate on it. Some GM do. lots of piston slap on Vortec but most time Quite down after it runs awhile. The motor has no idea how you feed it gas. Carb are EFI.
One other thing to check if all the other ideas fail. I've had two times in my 45+ years being a mechanic when the fuel pump was the cause of a knock on a SBC. All you need to do is just remove the bolts and let the pump hang. Start the engine up and you'll know right away if it's the fuel pump.
I concur with Wdobos. I had a knocking GM crate 350 in my 32. The problem turned out to be the chrome aftermarket fuel pump. Check it. You might get lucky. Sam
I have no stroker experience. But, all the motors with piston slap I've seen got quieter with heat. Winter time & initial start-ups were the loudest times. Some builders in desert climates prefer to run the pistons on the loose side.
I have a crate engine that had similar noise, it had the race type oil pan on it . Dropped the pan and the scraper rail inside of pan had a mark were the connecting rod was nicking the rail. I don't know if your pan has this rail in it or not. Always look for a witness mark inside of bottom of block or pan. My knock was louder at idle on cold engine and would fade as rpm increased.
First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen. If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back like a Marine Corps marching band coming toward you in the parade. Thanks to Dave... from. www.remanufactured-engines.com
Read post #4. It sure sounds like piston slap. In engines built with forged pistons, piston slap is pretty much an expected sound with a cold start. The slap normally goes away in short order once there is a little heat built up and the pistons expand. They have to have a larger piston to cylinder clearance due to the high coefficient of expansion of the forging, In most all common crate engines, and factory builds, the pistons are not forged, but rather castings, some hypereutectic. In either case, they do not expand nearly as much as a forging, so if the piston to cylinder clearance is on the large side of what is specified by the piston manufacturer, there will be some slap, and it is not as likely to go away with a warmed up engine, although it should diminish some. Sloppy manufacturing and assembly are to blame.
If it truly is a 96-00 engine there is no provision for a mechanical fuel pump. Piston knocking usually gets better as the engine warms up, but it was stated it gets worse as it gets hotter. Sounds like it isn't a GM crate either. You need to put a stethoscope or some sort of listening device on it to try and pinpoint the noise. Strange that it improves by advancing the timing, maybe there is an issue with chain/gears? You may have to tear it down to figure it out.
My ZZ3 crate SBC is the same way. Forged piston skirts shrink when cooled down for a long period. When warmed up, the skirts expand and everything is fine with my world again. It has 400 miles on it now and I expect the noise will never change in my lifetime.
Is this a factory GM crate motor or one from an engine remanufacturing outfit? As far as flexplate/flywheel one piece seal versus two piece seal will not interchange; bolt circle pattern is different. Sounds like the place that sold it doesn't want to warranty it and is trying to lay blame on your induction system which is a bunch of bull. There are a lot of piston manufacturers that lack quality control in their process sizes vary greatly.
Are you sure your balancer is accurate and not slipped on the rubber ring. They will tell you stories about your timing and set you on a wild goose Chase.
might even be a cracked piston....next time you take it down use Dye Check and a black light source to examine each piston around the pin area....engines SHOULD NOT KNOCK!
Since this is a 383 engine...MAYBE the block clearancing is off a touch...I say take it apart and look for marks on the block and rods...either way it SHOULD be a WARRANTY issue.
Its hard to believe the engine builder wouldnt want it back ASAP since his name is all over it.... Man, when I build an engine, if something ever goes wrong, I am all over it. Its usually an easy fix if it is cought right away. SO the supplier wont take it back?? The induction method be it carb or fi is only an issue for the cam profile. Good luck. Theres always the BBB if its a company. I wouldnt want my engine knocking or ticking
I see you are in Australia. where did this engine come from? And was it a GM Performance engine, or was it built by a shop?
My crate motor knock came from a bad mechanical fuel pump. I chased my tail on this for almost a month...
I had that problem on a 350 that I rebuilt, pulled it apart 3 different times and nothing was wrong. Eventually bought a crate 350 and pulled the rebuilt one out to find out that the flywheel bolts were loose. At least I had a fresh motor for the next project I did though.
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