alright so i bought an 89 iroc w/ a rebuilt 355 on it, it had about 500 miles on it and the seller told me it just spun a main, so i bought the car. My neighbor thought it was a wrist pin knock or a rod, and then him, my dad and my friend all think its a rod knock. It knocks LOUD n sounds pretty nasty, knocks on acceleration too like a rod, but it has good oil pressure, like 45 on start up. I heard about cracked flexplates acting like rod knocks, how do i go about checking for that?? I figured id check that before i pull the motor.

 

do you have access to a shop?disconnect neg battery cable. if so jack the front and back of the with floor jack, lift as high as possible (DO NOT GO UNDER CAR UNTIL YOU PUT JACK STANDS UNDER ALL 4 CORNERS SAFETY FIRST) place trans jack under trans loosen crossmember bolts, let down very slowly (have someone watch the distributor so it doesnt hit the firewall) unhook trans lines from trans loosen the bottom two bolts on trans from engine( i didnt have to unhook starter ,you may have to) get two long bolts to put in each side of trans in place of short ones(these will be used to slide the trans back) loosen the three torque converter bolts, now loosen the rest of the trans bolts.at this time push the trans and converter to the back of the car this will give you access to flex plate. you should have enough room to see if the flex plate is cracked(most of the time theyre cracked around the crankshaft)assemble in reverse.hope this helps .later jimmy

 

no i dont have access to a shop, this is being done in my garage with no heater in buffalo loll. damn i didnt think it was going to be that involved, sounds like more work than pulling the motor.

 

pulling the engine is a hell of alot harder, ive done bothits really not that hard if youre mechanically inclined ,if not it is a bit much to do,later jimmy

 

I'm betting it's a rebuild problem. I've encountered: loose flexplate to crank bolts, loose T/C bolts, cracked flexplate, spun rod bearing, collapsed piston, and broken crank before.
You can isolate the flex plate problems easily.
If you listen under the car, the noise will be louder than above the engine.
Do a stall test. (safely, with blocks)
Cracked flexplate and loose bolts will make the most noise at idle in neutral.
A little less in drive at idle, and much less above 1/4 throttle in a stall test.
Crank problems almost always get louder as the rpm rise. Even in a stall test.
I had one knocking engine almost out when I noticed I didn't need a wrench to take out the torque converter bolts
(they are hard to tighten by yourself)

Better yet, post a video that we can listen to, and you'll have OHpinions galore...

 

I'm about to start tearing this thing apart pretty soon. CAN rod knocks have oil pressure?? How do I preform this stall test? I wish I had some way to get a sound clip or video on here but I cant. It sounds like a really bad rod knock, like the piston might even be hitting the valves, either way its loud.

 

I'd say it sounds similar like this guys video except louder:

http://youtube.com/watch?v=wIJ-CfNpcYg&feature=related

 

Take a piece of old garden hose and listen. move end around motor stay out of the fan. listening through the hose will help isolate the noise. top bottom frt back.

A new high volume oil pump will hold pressure with a spun bearing. My son has one just like that. bad knock spun bearing. lost oil presure started knocking, pressure came back up.

 

Yes. Bad rod bearings won't greatly reduce oil pressure. Oil pressure is maintained by the main bearings.

Bad bearings either a spun main or a bad rod usually means the crank will be damaged. How much is repairable depends on how much damaged. A spun main bearing usually overheats the web, damaging the block.

Knocking noises inside the engine usually mean a new engine. The cost of a rebuild can be more expensive than a new replacement engine.

That would send up warning flags that the rebuild was very poorly done. Slapping a set of bearings and rings in it without checking clearances isn't a rebuild. Chances are it was a home rebuild and not done by a shop that would warranty the work.

 

Alright so I guess ill just pull the motor, check and see if the flex plate is alright, if it is, then i guess ill just buy a new short block. Any suggestions on short blocks?? I was thinking about the L31 block, its reasonably priced at about 1300 bucks. Its basically the same as the zz4 i think but without a forged crank which i dont need, the zz4 is too much money.

 

Or how about this thought.

Good high dollar rebuild. very poor break in. Wot way too eary.

Stephen very nice car.


Let me see....

I want that for my DD is it doable for $1500 next week.

 

Thats my guess because when I went to look at the car before it started knocking it was a quart low on oil and I think the guy did beat on it a couple times before with only like 250 miles on it. Also it has synthetic oil which you arent supposed to use to break in an engine. Either that or he didnt tighten something right

 

Today breakin oil from factory is syn.

To do everything but rings.

After the first oil change the rings get seated.

I put syn back in at 5000 miles.

 

ok my problem is once the engine gets warm u start to here a knock and the oil pressure drops o like red zone area when its cold it dont knock. when its warm and it knock after im going down the highway or acceleratingly the knock goes away cuz the oil pressure is up. its still about maybe 15psi tho. dk what it is...loose flex plate? rod? push rod? lifter? crank?? maybe bearing clearance????someone help please?

 

Oil pressure needs to be 10 # for every 1000 rpm.

My guess is you have a high mileage engine. The knock you hear is the bearings last breaths (away too much clearance). Low oil pressure 15# at road speed = new motor. Factory new is 40# at 2000 rpm, and 20# at idle.

 

SOURCE OF KNOCK WAS A MISSING CAM RETAINING PLATE!! Once the new timing chain loosened up the cam was allowed to move back and forth knocking against the block. Meanwhile I had all the pistons apart (without numbering them doh!) i slapped some new bearings in and got a new cam plate and timing chain and fired her up. No knocks so far, just hoping my rings will still seat.

 

ya i was told that the motor was rebuilt

 

if your oil pressure is low put in thicker oil *awaits nay saying thin oil lovers*

 

just dont put in 20w50. that stuff is like glue.

 

5w-30 .0015 oil film
10w-30 .002
10w-40 .0025
15w-40 .003
20w-50 .004 unless at 300 degrees in a air cooled Harley motor .002

A race motor, makes a lot of heat, and is built to race standards. This heat makes the parts grow bigger in size and removes the clearance (more clearance allows for block twisting at high torque loads). When ran on the street not enough heat is built up so everything is way to loose.

Fat oil fills big holes, if heavier oil decreases knock then bearings are loose.

Try retarding timing, knock will leave if timing too much.

Too lean at high load will also "knock"