Engine Clanking

[hondarider188]

in my 1983 chevy k10 it had an engine swap to a 5.7L by the PO and when I got the truck it has run great until the last few weeks. it started making a weird clanking noise. initial thoughts were either a bad lifter or just valve lash. I ruled out those two though because the noise is loudest underneath the engine towards the bell housing. yesterday I pulled the dust cover off of the bell housing and inspected the flywheel and torque converter and everything seems to be tight and in good order. a friend of mine said it could be the oil pump. and my oil pressure gauge doesn't work so I'm not sure where its running at right now either. the noise is very erratic and isn't always there and comes and goes as I drive. it seems to do it most when the engine is running down from letting off the throttle but goes away again when I give it throttle and engine is under load. is it possible it could be the oil pump or should I look at something else first.

[BADAZ chevy guy]

I had a wrist pin do the same thing once. Knocked when slowing and went away under load.

[hondarider188]

i had read about wrist pins doing this but i wouldn't think that its loudest on bottom end of engine. also i noticed while driving today that it changes through gears of the transmission. so when it does it in park but doesn't do it in reverse and if so its very quiet then all the drive gears also make the clanking noise. so could the transmission be at fault.

[bd]

Connect a mechanical test gauge to the engine and check the oil pressure.  Pick up a 3-foot length of straight 1.25" rubber hose to use as a listening tube and locate the source of the noise.  If the engine is knocking, find out what's causing it before it's in pieces.

With the engine OFF, pry the crankshaft fore and aft - how much does it move?  Does engine temp have any effect on the noise?

When you inspected the flexplate did you look closely for arcuate cracks through the plate near the crankshaft flange?  They can be difficult to see.  Are the torque converter bolts tight?  What condition is the oil in and is it full?  How many miles on the oil and filter?

[hondarider188]

so i haven't gotten a chance to check the oil pressure so i think i will try and do it Monday just to check it and make sure my pump is still in good order. Yesterday I did a lot more research online of things that could cause this, and one thing that seemed to come up a lot and bd mentioned it and that's the flex plate being cracked or broken at the crank bolts. when i took the dust cover off the first time all i did was check to make sure the torque converter was tight. so last night i took the cover off again to see if the flex plate was cracked, and sure enough it had a split straight on through it. it seems i need a new flex plate. so i have a few questions about changing it now. Will i need to drain the transmission and transfer case when i move them back or not? and also i forgot the count the number of teeth on the flex plate so does anyone know what size i would need( 1983 k10 5.7L TH350 trans). I saw some online with either a 153 teeth or 168 teeth, which one?  Thanks

[dvdswan]

you shouldn't have to drain either the trans or t/case, but you may need to cap off the trans lines to the cooler so they don't leak.

I've heard the 153 is SB and 168 is BB, but personally don't know.  you should be able to move the trans/t/case back as a unit about 4" to gain access to the flex plate bolts.  you shouldn't need to remove them.

[bd]

The flexplate on your truck has 168 teeth.  Unbolt the converter from the flexplate and slide it toward the transmission BEFORE unbolting the transmission from the engine.  The converter is heavy and may try to slide forward as you move the trans away from the engine - be careful that it stays in place on the transmission. 

Notice that the flexplate has raised mounting pads for the converter bolt bosses.  Look at the flexplate before removing it and install the new flexplate the same way.  Use a torque wrench when attaching the new flexplate to the crankshaft.

[hondarider188]

all right thanks you guys ill try and get a new one put in soon. what does the flex plate and the converter be torqued to. also i read on other sights that the reason the plate would have cracked is the engine and transmission are out of alignment in some way, is there any truth to this and if so where do i need to look for an issue at.

[bd]

Find the torque specs at the back of the Engine Section in the 1983 Service Manual.

Flexplate cracking is a normal consequence of metal fatigue caused by repeated distortion.  The converter is a heavy rotating mass.  As it accelerates/decelerates with engine RPM, the converter thrusts forward and rearward, distorting the "flexplate."  Eventually, the plate can crack as you experienced.  Left uncorrected, the center of the flexplate can rip out entirely. 

The transmission is indexed to the engine by two ~5/8" steel alignment dowels.  When you slip the transmission back check that both pins are in place, there is one on the left and one on the right.  If either is missing, check that the dowel pin boss isn't broken then install a new dowel pin.

For just a little more money consider a heavy duty replacement flexplate.  And, measure the endplay on the crankshaft as I suggested earlier.  Allowable endplay is also published in the service manual at the back of the Engine Section.

[hondarider188]

bd is there any reason why you recommend the heavy duty flexplate.I thought stock was sufficient until you were pushing at least 450hp and risk the flexplate shattering and ruining the engine. as of right now and as far as I know this engine will probably never reach that high. I know I might as well upgrade while Im there and doing a swap, but price is always a big factor. I'll get the better flexplate if its really needed but if its just more of a preference I might save a few bucks and run a stock replacement.

[bd]

It's purely optional.  The standard flexplate should be adequate for your purpose.

[hondarider188]

all right thanks for all the help.

[hondarider188]

ok I have one more question I have everything on the transmission disconnected and ready to come out except for the detent cable. im not sure how to disconnect the cable from the transmission to leave it on the truck. if I unbolt it from the case on the tranny I can slide the sleeve up but the cable stays attached to the case. so how do I remove and install it again. thanks

[Captkaos]

The cable just comes off of the carb, just remove it....

[LeftysRodandCustom]

 Looks like you found the problem with some great help. Definitely obtain a manual oil pressure guage. Its very cheap insurance really. Also, Bad Az Chevy Guy, be very very wary of anything making noise under deceleration in a chevy. Having grown up in a racing family I have probably seen as a conservative guess 500 or more chevy small blocks blow up on the track. 99% of those blow when the driver lifts out of the throttle at the end of the straight. When they're old and worn the just wont take the lash.