KITT87

Hey all, sorry if this thread is redundant at all, I have used the search and read a lot of old threads. Recently I replaced injectors, got delco rapid fires, set timing, and set idle speed on my 87 v6 bird. Afterwards, when my car is idling in any gear, I can hear the what sounds like a rod knocking. There is a chance it was doing this before but I just couldn’t hear it over the high idle. I used a long screw driver and could not find the sound, and I can’t hear it under the hood unless I lean all the way back towards the fire wall. I can hear if the most clearly when I’m sitting in the driver’s seat. It almost sounds like it’s inside the dash but it’s not. It goes away when the rpm raises (not rod knock?) but before it goes away it does seem to raise with engine RPM.

I do not believe it is spark knock (but I will be checking timing again soon) because it is deeper and sounds like a rod knocking. Which brings me to my flexplate questions:
1. Can a cracked flexplate or loose flexplate bolts/loose torque converter bolts cause these symptoms? Maybe it’s not the flexplate because it still makes the same noise in park and neutral?
2. I’ve read the process for replacing the flex plate/checking it. Would you guys personally consider it a difficult job? I would like to attempt it myself but if it’s too much I would rather pay someone to have it done better than I could.

Sorry for the long post and for posting yet another question. Thanks in advance.

ACebell

Yes - a cracked flex plate can cause a "knocking noise" - I had a 90' Silverado, that had a same issue. It's not a difficult job to check, swap it out. Just need some ramps, or good quality jack stands, a floor jack, and some straps. A transmission jack or saddle adaptor would be a bonus. Patience and a friend to assist is a must as well. It's kind of tough (can be done) to "marry" the transmission back to the engine when done. And from my onion experience, double check the flex plate bolts are torqued BEFORE putting it all back together.

KITT87

Thanks for the info! I’m about to go out of town for a Judas Priest concert but I’m gonna look into it more when I get back

KITT87

Here’s another dumb question while I keep looking: how do I know how many teeth my new flexplate should have? I read on the V8s you can tell by how the starter is mounted, not sure if it’s the same on the V6. Looks like hawks a 148 tooth one and GM genuine has a 153 tooth one.

ACebell

Not a dumb question! I just do the old school method ad count them!

Here is what Rock Auto Shows for your application:

1987 PONTIAC FIREBIRD 2.8L 173cid V6 Flexplate | RockAuto

As for the concert diversion? Well.. It's Saturday Night and the Priest is BACK!

KITT87

Yeah I saw the GM genuine 153 tooth on rockauto, don’t think the other two had teeth listed. I’m probably just gonna go with the GM one.

And amen brother!! This will be my first concert and I’m really excited for it.

OrangeBird

iTrader: (1)

By all means, check it for cracks/looseness before taking anything apart......

KITT87

For sure! I just wanted to make sure I was on the right track first

OrangeBird

iTrader: (1)

Hi KITT87,

I would get under there with the inspection cover removed and start by grabbing the torque converter and twist & wiggle it to see if it's loose from the flexplate. If it's bolts do have it tightly held to the flexplate, next try carefully wiggling & jiggling the flexplate using a small wooden stick/dowel to see if it's has play where it's mounted to the crankshaft. Bonus points for rotating the flexplate/converter 360 degrees while carefully looking for cracks in the flexplate. Thing is, it's not really possible to see cracks or loose bolts where the flexplate mounts to the crankshaft, but any crack/looseness bad enough to produce knocking sounds should be detectable as play while doing the wiggle test.

KITT87

Well, I did all of this (man that one inspection plate was stuck in there!) and didn’t see any cracks, nothing felt loose, and I ran it with plate off and everything looked fine and normal. There was some oil around and on the inspection cover, but that could be left over from my distributor leak I fixed. I listened to the bottom end and it does make noise but not an “I’m about to chuck a rod” noise at all. I think I’m gonna have to drop it off to get a diagnosis because I just don’t have time with school to take it apart and do a deep dive.