Torque Converter Bolts Backed Off?

[clockdoc]

I've put a little over 600 miles on a newly built 355. I started with an ATI short block and used the top end components from a 327 that ate its thrust bearing and roached the main webs. Early on there was a "chirp" that showed up intermittently, and always after the engine was warmed up thoroughly. I was never able to determine where the noise was coming from. I replaced all belts and corrected one belt alignment issue and there was no change. Following a very long traffic jam last weekend, on an 85 degree day, a much nastier noise appeared. It is a pronounced, knock/rattle that seems to be coming from the rear of the engine. The noise starts as soon as the engine is started and calms down a little after idling for a few minutes. When put in gear, it gets much worse. A light load on the engine quietens it down and, as long as there is a load on the engine, it is quiet. It runs great and sounds good on the road, but gets noisy again at a stoplight unless the idle is held up slightly with the accelerator.

I have concluded that the converter must have loosened up, but have not had time this week to get into it. I plan to get back to it this weekend. Does it sound like I am on the right track? Any words of wisdom?

[geezer#99]

I’d bet on a cracked flexplate.

[clockdoc]

Thanks for the response. Would you expect a brand new flexplate to crack so soon? Truck has not been raced or driven hard.

[geezer#99]

Not normally but we live in a time of poor quality replacement parts.

[clockdoc]

I just realized that I posted this in the wrong place. Should be in 1973-1987 forum. How can I remove the post from here

[geezer#99]

Ah!
You are in the 73-87 forum!

[clockdoc]

Obviously I don't know what I'm doing.

[Matt Man]

I just had the same situation in my 81, I would drive mine on the freeway then it would start knocking when I got off the freeway. I checked my converter bolts and they seemed tight or so I thought. I had a shop replace my converter because I wanted a 4x4/towing application with brazed converter fins. Well I also had them replace the flexplate and converter bolts while it was out and sure enough the other shop that rebuilt my transmissions drilled out the flexplate bolt holes because the new 59$ converter didn't like up. Plus the 59$ converter didn't have long enough threaded holes and the screws bottomed out... cheap a**holes. How could you not notice the bolts bottomed out... I should have known better and threw in a higher quality converter but I was moving at the time and was pretty strapped for cash. Buy once cry once.

[Tom]

Cracked flexplate. Happened with my new engine too. New TCI plate and it lived happy ever after from that point on.

[clockdoc]

The flexplate is cracked and at least two of the flexplate to crank bolts are loosened. The flexplate was from SCAT and the converter was a Summit unit. Both were new 600 miles ago. Guide pins in the block are new (came in the short block). I torqued the crank bolts (ARP) to 65 ft-lbs. The converter was installed by the engine installer. Any suggestions as to what I should do to hopefully avoid this happening again?

[geezer#99]

What did you get for a new flexplate?
Are there any star washers on the crank bolts?

[Wikid61]

Pix would really help the cause.

[clockdoc]

I haven't bought a new one yet. Not sure what to buy. There were no star washers on the crank bolts.

[geezer#99]

Like Tom said.
Get a TCI.
And some correct bolts and washers.
https://www.jegs.com/p/TCI/TCI-Heavy...46478/10002/-1

[MikeB]

Good quality flexplate bolts: https://www.summitracing.com/parts/a...2902/overview/



The T/C bolts are 230-7303 or 230-7304 depending on trans type. Then again, some T/Cs have "nuts" welded on, so you would need only bolts with correct threads.

[clockdoc]

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

[Bloodhound]

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

You just made me have a mini-heart attack and go back and check what I recently installed. Fortunately it was the 200-2906. Good luck with yours.

[clockdoc]

Glad it was just a false alarm!

[MikeB]

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head.

Good catch! Looking at Summit Racing's website, you'd never know there's a difference between ARP flexplate bolts for 1-piece and 2-piece main seal blocks. In the future, I'm going directly to ARP's website.

I installed a 1-piece main seal 350 in my truck four years ago. Just spent nearly an hour looking through paper invoices and on-line orders, but can't find what I used for flexplate bolts. I have a couple thousand miles on the truck since then, so I'm probably OK.

[clockdoc]

I'm going to ask what is probably a stupid question but, because I have become so paranoid about overlooking something, I'll ask it anyway. Given the one piece rear seal block/crank, does it make any difference whether I use a 153 or a 168 tooth flexplate as long as it is externally balanced (other than the starter)? The truck went to the transmission shop today.

[MikeB]

Originally Posted by clockdoc

Given the one piece rear seal block/crank, does it make any difference whether I use a 153 or a 168 tooth flexplate as long as it is externally balanced (other than the starter)? .

You can use either. Just make sure the starter and the dust cover work with the size you choose. Many aftermarket starters have two sets of mounting holes, whereas OE starters do not.

In my experience, the 153-tooth flexplate is more header-friendly because it tucks the starter in closer to the block.

[Tom]

Originally Posted by clockdoc

Thanks Mike. These are what I had used initially. Turns out they are not intended for this crank/block (1986 and up, one-piece rear seal, Gen l). The correct ones are apparently 200-2906. They are .725 long rather than .680 and have a 5/8 head rather than a 3/4 head. I have ordered a set, along with a B&M flexplate (TCI had only one that could work, but I would have had to drill out the converter holes) and I plan to take the lot to the trans shop Thursday. I really appreciate your response. Looks like I didn't pay enough attention to detail the first time around.

Annnnnnnnnnnnd pretty sure you just figured out my intial problem as well. MY setup was a vortec 350 mating to a 200-4R, replacing the original 350 and th350 trans. I re-used the TC bolts. Flexplate cracked, I went TCI with ARP bolts. Bet I ordered the correct TC bolts when I got ARP and hence no more problems....

[clockdoc]

Many thanks Mike. I am going with the 153 tooth plate.Probably wouldn't have thought about the headers but it makes sense. Thanks again.

[clockdoc]

Sometimes what seem to be non-issues bite the hardest. glad you are back and running well. I think I will be early next week.

[clockdoc]

Thanks to all of you who offered advice. I have the truck back now and have looked at the flexplate closely tonight. It is a Scat plate and is either powder-coated or painted black. The six crankshaft bolts were loose enough to remove by hand. I'm not sure the plate is cracked, as I had previously thought, but the black coating has numerous stress cracks radiating from the torque converter holes. I plan to remove coating from one of these areas and see if the plate itself is cracked.

I just found this 2012 post on the Corvette Forum:

https://www.corvetteforum.com/forums...nTiY9sJc.email

The problem described in that post is exactly what happened to me. In addition to flaking under the bolt heads, there had obviously been fretting between the crank flange and the flexplate at the bolted connection. The coating there was basically destroyed.

There is too much similarity between the poster's experience and mine for me not to believe that the coating was the culprit.