I bought this 350 about a year ago and it's done mostly sitting however there is a knocking sound during start up for about 15 - 30 seconds afterwards it dies down. It is RPM sensitive. Is it possible the oil I have is too heavy? I used the recommended 10W - 30 but oil pressure is over 60 at start-up (my first sign it would be too think to be be lubricating properly.). I've done a search and about the best ideas I could come up with was piston slap and needing slick 50. I heard you're not supposed to use slick 50 until you have over 50k miles? This engine has $1000 miles and it does sound similiar to the rodknock I developed in the L69. I'm not a big fan of replacing this engine again so any information is helpful. Thanks!

------------------
1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

 

FTA,

Ouch - 1,000 miles and it knocks ?

Since it has oil pressure, I'm going to say it's probably a rod bearing - son of a beech.

The motor is broken in already, so you can try a 15W-50 like Mobile One synthetic.

This knock could also be piston slap, especially if it's a forged piston motor, or, a cast piston motor that was an "Auto Zone" or similiar rebuild.

I'd probably pull the oil pan and wiggle the rods - if one is loose enough to knock, you'll feel it. If not, and it's piston slap, well, live with it - it's fairly innocuous.

Mmmmm........I hope you did not pay a lot for this motor.....'cause any way you cut it, it should not do that.

Note: The old ZZ3 GM crate motor was notorious for piston slap, until GM started using hyper-you-eclectic pistons.

(Really diverse pistons, uncommon)

Good luck.

BOR

 

Thanks for the reply. I'm leaning towards piston slap myself because usually rod knocks end up happening after it warms up and the oil thins out. The pistons are cast for sure. It was the $1350 special . Once I'm done with it I'm only looking for 350 HP (Hardtop is getting a monster engine though). I listened to a recording of my L69 rodknock I had made and this is a little bit duller not as high pitched metal clinking.

Heh. I'm not pulling the oil pan because if I find a loose rod it's going back or if it throws a rod it's going back (3-year warranty)....so either way.

Is there anyway to "solve" piston slap or do I just have to live with it?

Thanks.

------------------
1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

 

That sounds more like a cam lobe...

Those will make a sound that is almost hollow, not quite like the clattering sound that a rod makes. It typically happens when the motor is cold, and more so when it hasn't been driven for a few days.

Rod knocks will happen more when the motor is hot and the oil has thinned out. Piston slap sounds more like somebody knocking on a door and is very fast, since it will make 4 knocks per complete engine cycle (2 crank revs). A cam noise will occur once per engine cycle, a rod twice per cycle, and piston slap 4 times per cycle.

------------------
"So many Mustangs, so little time..."

 

FTA,

RB83 brings up a possibility - it's not common, but at least it's readily identifiable.

What to do about piston slap ?

Live with it. Most race motors slap like crazy when cold because they are clearanced sloppily at the piston-wall interface.

Reduces friction and makes more HP.

So, maybe you're getting a few more ponies from this deal, huh ?

Well, see, the cups half full........not half empty.

BOR

 

Exactly what it sounds like. A knock on a door/wood. I was just tapping on wood last night thinking that was exactly what it sounded like. It's about as frequent as my rod knock was though however other people that heard my rod knock suggested that there were multiple knocks because it sounded quicker than any one they had. Thanks for the replies. I highly doubt it's a cam lobe, I pulled the plugs, they all look good and the engine is definetly running on all cylinders and runs smooth once at op temp. I may throw a small bit of slick 50 in just for good measure.

------------------
1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

 

I feel your pain. I just sent my brand new zz4 short block back to S.D. because of a bottom end rattle.If you are unsure of where the rattle is coming from (top or bottom end) try using a timing light as a refrence beat. If the rattle matches the beat of the light = top end, two rattles between flashes= bottom end. Hope this helps.

------------------
87 IROC -
ZZ4 350
SLP T-Ram,1"3/4 SLP headers, Cat back, Hotch-kis, MSD, Iebach etc.

 

My 89 T/A GTA with the stock L98 does exactly what you are talking about. depending on how cold it is outside, it will knock from 15 sec to 1 min and then just dissapear. I've had the car for 2 years and it has done it ever since I've bought it. It hasn't gotten any worse, and consistantly runs high 14's with 130,000 miles. It sounds like piston slap becuase it is not rythmic like a a rod bearing, or lifter. Just sound like more of a rattle coming from all 8 cylinders. I wouldn't worry about it.

89 Transam GTA, a few bolt ons

 

I fixed a truck a few months ago with piston slap. You could barely hear it at an idle but when reved up it made the knock, knock sound. I originally though rod bearing so I pulled the pan to inspect it (lots of room to pull the pan while still in the truck). All the rods and mains were OK. When I looked up into the cylinders under the pistons I could see scoring on the #2 cylinder wall.

I pulled the head and pulled that piston and con rod out. The piston didn't flop around on the wrist pin. It was too tight and was causing piston slap. I ball honed out the cylinder to remove the scoring and put some cross hatching back on the walls. I installed a "new" piston, wrist pin, con rod and rod bearing. Reinstalled the head etc and fired the engine up.

The knock went away. This engine was less than a year old.

------------------
Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Did you find an anwser to this yet? I was looking for something else and saw this post again. It sounded like a lifter tap to me since it goes away soon after starting. Piston slap would take longer to go away, and a bearing noise wouldn't go away.

A good engine flush can clean a dirty lifter IF the the offending substance is soluable (like varnish or a chunk of sludge). If it is hard (like a sand particle) the flush wouldn't help. Sitting around seems to promote the former type of behavior. AMSOIL Crankcase flush is an excellant choice (much better than the normal stuff you find on parts store shelves) to see if that is your problem.

------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

I'm not any great mechanic but I heard before that a engine will knock if the gas isn't a high enough grade if your not using premium try premium. I used to work at belle tire and they sell amsoil products and that engine flush works great. My friend put that stuff in his engine that had 90,000 miles in it and it started burning more oil. But your engine is new so it won't damage anything.

 

here's some good info on motor oils and without reading this article I wouldeven advise not to use Slick 50 because you would be wasting your money. Mobil 1 is definetly worth the money though.
http://www.centuryperformance.com/engineoil.htm

------------------
1988 TA 300+hp 350 w/ TBI and Holley TB unit, Holley projection intake,
WC T-5, 3.42 gears w/ Auburn posi. MSD 6A, edelbrock TES headers, dynomax 3" cat and cat-back system, ACCEL coil, polyurethane bushings all around, aluminum driveshaft, Mr. Gasket open air cleaner.

1993 S-10 w/ 4.3L V6 TBI, slightly bigger cam, Mild polish job and 3 angle valve job on heads, Edlebrock TES headers, Dynomax cat back, MSD 6A, ADS chip

2000 Kawasaki KX 125

 

Thanks for the follow up. I never discovered exactly what it was but it went away which could be something in the lifter that slowly dissolved. The knock from gas is a predetenation knock but thanks for the suggestion.



------------------
1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration
13.98 @ 101

 

I just converted a '90 Bonneville SSE that had 108k miles on it. It used a qt/4000 miles on petroleum oil (bought it w/104k miles). It used almost 1/2 qt in the first 1k miles w/synthetic. I topped it off before going on a 370 mile trip at Christmas - it used 1/4 qt on the way there. When we got back, it was still 1/4 qt down. In 400 miles around town since, it has barely moved from 1/4 down.

A poorly maintained engine might use oil after the flush is used because varnish that was helping to seal things up has been removed. But, the "rest of the story" is that oil usage will typically go down as the synthetic use is continued, unless there is something mechanically wrong with the internals.

84FTA, have you had two different noises, one of which has now disappeared?

 

Uhm...one noise...I have many including a header gasket leak being the newest . The one that sound much like piston slap has disappeared but there are still a few wierd ones like a whistling, a whining (mostly tracked to the alt.) and the sound of a loose belt.

------------------
1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration
13.98 @ 101