You posted: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 Put a F I on it & when it still knocks tell them they owe you.
its the roller rockers. i had a 302 with full roller rockers and they are noisy and when i built my 331 i used full roller rocker arms but a different ratio and they too are noisy. i did some research and asked some questions and found that it is normal for the full roller rocker arms to make some noise.
my 99 silverado had piston slap like a sonofabitch, but it would quiet down once it was warm, as piston slap is apt to do. does the noise change at all when the motor's at operating temp? plenty ls engines run fine with carbs. your builder sounds a little shady to me.
Thanks guys, I appreciate the help. Things that have been done already : - Run with mechanical fuel pump removed (no change to knock) - Run with individual plug leads removed (did not isolate to a single cylinder) - Rod to block clearances checked - Rod to pan clearance checked - Valve gear condition and clearances checked - Bearing condition checked - Piston, ring and bore condition checked - Timing gear condition checked Things I will recheck : - Flexplate - Flexplate bolts - Try the stethoscope thing to try to isolate location - Try Two squirts of engine oil into cylinders - Further play with the timing This engine was purchased through one of the large US on-line automotive stores who say it is the engine builders warranty so see them. The engine builder offers no suggestions of things to check or possible causes, just goes on about the FI. So we suggested piston slap and they said they have never had it but, if we send it back they will have a bit of a look at. And yes, I am in Australia, so sending it back is a major issue. I am not keen on shipping it back, then it comes back to me with the tag no problem found and an invoice for their time to pull the motor down. I have already spent money for 3 days work in a very experienced, professional shop for diagnosis, hoping to just get it fixed. The inside of the engine is perfect . Their best guess was piston slap caused by the stoker/short piston skirt combination as they have previously seen it with certain Ford stoker combinations.
For your consideration: You leave out some important detail but: You say "that makes it sound like a diesel at idle." Based on what there is to go on that sounds like preignition to me. That will make an engine sound very much like a diesel. If you are trying to use 87 octane fuel on 9.25 cr you are on the ragged edge of knock threshold . Your engine is a computer controlled engine. In stock form it has a knock sensor that keeps the engine right on the edge of "Knock" by retarding the spark. Don't be too quick to rip the supplier, you have taken an engine designed for a precision fuel delivery system (fuel injection), a precision computer controlled ignition, and fed it with what is basically a drooling tin can while firing it with ???. Set your distributor to 0 to start. Feed it a little high octane. High octane will slow down the burn a bit. See what happens. It appears you need a distributor that will retard enough at idle to stop the detonation and still advance enough at higher rpm. Without the computer controlled timing you are not making full use of the capabilities of the engine.
I've worked on cars for 40 some years & to find piston slap I used to take off the air cleaner start the vehical up & slowly pour a small stream of STP down the carb. If the noise went away = piston slap. unkledaddy has the same idea, but mines a little easier.
Removed from a 38 Dodge pickup and not a stroker motor, but, we just tore down a buddy's 4 year old Chevy 350, 290 HP, Made in Mexico GM crate motor, for knocking. One cam bearing was installed to deep blocking 1/2 the oil gallery hole in the block. One rod bearing and one main bearing had started to flake bearing material. Seems that QA was MIA in the engine plant.
I agree with the preignition comment above. You also want to ensure you are not getting any crossfire in the spark plug wires. You also need to check & make sure the oil pump pickup is not sucking air or is loose on the pump - I've seen that. I had a 383 that started knocking after about 6000 miles. Turned out to be an issue with the full floating rods (1 rod had a sight twist) - I don't think that is your problem though, unless they are full floating. You need to remove the pan & watch the crank & rods while the engine is rotated by hand, & check the inside of the pan for any contact as previously suggested. What grade of oil? How is the idle oil pressure? Can you get the casting #'s off the block?
short skirt coated pistons =less friction for more mileage but piston slap when a little coating degrades and opens up the clearances .
Didn't the vortec head require little ignition timing, like less than the usual 32 degrees? If so, and perhaps the engine that could got set for a "normal" timing level, that could be the knock? Occum's Razor and all that...
A knock that goes away with increased initial timing or acceleration most likely is going to be timing related. You probably want a re curve so you get a little more initial and a littles less total . Or your balancer marks are off.
Its running on 95 octane. My earlier statement of "advancing timing reduces knock" wasn't correct. If you change the timing from 10 deg static to 20, the knock goes away, but that is because the rpm goes up. Drop the rpm back to normal at 20 deg static and the knock is exactly the same. Interestingly, the "couple of squirts of oil in all the cylinders" didn't get rid of the knock at all. And the knock definitely gets worse as the engine warms up. Checked flexplate etc. All look fine. Changed the distributor drive in case there was an issue there. No change.
If it has a mechanical fuel pump, it wasn't designed for EFI. These part store "crate" engines are a shot in the dark. I've heard many horror stories from shops who've installed the parts store engines, had a problem and couldn't get any warranty. The builders have a million excuses. Knocking can be caused by piston pins being too tight causing the piston skirt to slap. The pins can be too loose. The piston diameter can be too small at the skirt. The cylinder bore can be a little off. Everything has to be measured.
From your distributor instruction manual: " When selecting your advance curve, use detonation " Back off (retard) the distributor until the ping at idle stops. That will give you a starting point to figure the advance from. Verify that you have the vacuum advance connected as they require. They have information in their manual that applies to your problem.
Re: 9.25:1 compression, if it's using 96-00 heads and correct pistons for a 9.25 383, you'd have to have one heck of a low-end cam and then put effort into making it detonate. GM has run 9.5 compression since the early 80s in engines that work fine on standard octane like 87 in the states (we're different here; I think we run RON + something octane rating / 2 whereas straight RON numbers are used in AU or something like that) If you can hear it while cranking it over (without fuel) then isolate that it's not the valvetrain by pulling all pushrods and magnet sticks holding the lifters up away from the cam. Then if it's the bottom end, you can tell the original seller to take care of it or choke on a chargeback. Your dealings with the original seller are subject in part to your payment method's rules too. And hopefully you bought it rather recently. Good luck.
Ok not sure why you didn't respond to my question but i'll tell you what I'm thinking. I build alot of race engines and alot of perf street engines and now days it seems like the two are quite far apart !! Now when the two engine types cross over up come issues. The two piston types I see are forged replacement and forged race. The forged race have two valve reliefs or a trough for valve pockets. The forged replacements have four valve reliefs. All seems quite simple at this point. Now this is the twist, two relief pistons have centered wrist pins and four relief pistons have off-set pins. Still seems quite simple right ??? Wrong !!! If you use two relief pistons in a street engine be prepared for the Diesel Sound when the engine idles as the centered pin puts a side load on the piston skirt and makes the diesel rattle. The four relief pistons have off-set pins and this takes the pressure off of the skirt for a quiet engine. Now I'm not sure which piston you have but this is the experience I have had with these engines . I hope you get your problem worked out !!! >>>>.
The 4 relief pistons have a "front" to them (because of the offset pin)...the trough or two relief pistons don't.
Did a Flat washer get down the intake ? I have also seen a small ball of metal casting flash from the intake get on top a piston. If you have access to a good bore scope, you could check every cylinder for some type of contact.
Sorry for the delay in getting back to you Engine Pro 5X. I wanted get the correct information. The shop that has been looking at this says the pistons are KB type 135 which, from the datasheet for the piston, have a centered pin. The datasheet is : http://www.kb-silvolite.com/kb_car/performance.php?action=details&P_id=93 Maybe this is the issue. I have also heard that the shorter 5.7 rod (which are in this motor rather than 6.0) together with this short shirt piston, that has the pin at the bottom of the piston, could be prone to piston slap as well. There are no washers etc in the cylinders, intake or valley as the shop has already had the heads off and back on, chasing this issue.
Has the shop checked the skirt clearance? My buddy has a 383 with the same pistons and everything was fine and dandy till a cracked seat got a little water in one hole. After swapping heads it now has a subtle rattle that goes away as the engine warms up. We thought it was only steam, but was probably just enough water that got in to rock the piston and collapse the skirt.
I too am suspicious of the centered wrist pin location in the piston. At tdc the rod will be perfectly in line with the cylinder bore. Most pistons have an offset pin. In a multi cylinder engine, it is done primarily to always keep some side load on the piston to avoid a "knock" at tdc. With the rod inline with the bore, there will be no side load, thus the piston rocks in the bore causing your noise. Some of the stroker pistons are around 1 1/8", (1.125) compression height. Yours are 1 7/16" per attached data. I don't think that the height, or short design is the issue. A couple things lead me to suspect this. One, you can't isolate your knock to one cylinder. Two, as the rpms come up, the knock goes away. It sounds as your local shop has given the engine a very good going over. If there was an assembly error they most likely would have found it. I don't like new motors with odd noises either...sometimes all you can do is turn up the radio. Long story but, we have an inline six with one piston backwards from the other five. It's in a vintage race car for a shits & grins class so who cares? Runs like jack the bear. Has surprised more than a few v8 cars. It rattles loudly enough at idle you can hear it even with open headers. Pick up the rpms & it goes away. I'm certain it is due to the rod angle at top dead center. Good Luck, Worken2much
Videos of engine idling on You Tube : http://www.youtube.com/watch?v=yRT-HL8g_VM&feature=youtu.be http://youtu.be/t3-o69V3mB0
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