You sure it's not detonation?

 

Yea I'm sure it's not detonation, wouldn't that cause misfires and backfiring?

 

More often it is converter bolts to flexplate are loose, or the flexplate itself is cracked in the area around the crankshaft hub bolts.
Broken flexplate is a fairly common issue.

 

Had this problem in 2021...torque converter bolts were loose at that time, no cracks in the flex plate at that time either...

 

To check for detonation just pull your initial timing back 4 degrees.
If the noise is gone you’ll know it’s source.

 

This is cold start at idle...you can't really hear it from the top of the motor, but you can hear it really good from underneath right at the torque converter...

 

I've checked the tightness on 2 of 3 with a 9/16 wrench..haven't caught the third one yet turning it over by key, kept firing up at the flick of the key lol

However I noticed one bolt looked to be inserted crooked..

 

You may wanna pull them bolts. Looks like maybe the wrong type of bolts.

To turn the flex plate, take a big vicegrip and grab the part just inboard of the teeth. Turn the direction you want, the VG will swivel until it touches the teeth. Continue gently and it will turn without damaging the teeth. This method works perfectly for tightening the bolts as well. The vice grip will jamb up against the bell housing as you tighten the bolts.

 

Yea I'm considering on replacing the bolts today. Should I use Loctite on the threads ?

I'll bump it with the key or use a flat tip screwdriver against the bell housing...really wish I had the flywheel turn tool...it's a future investment...

 

You don't own a vice grip?
Detailed method posted.

Locktite, a guy can always get the bolts open, so it doesn't hurt.

 

Not a big one, I have two smaller Pairs and one is needle nose.. my grandpa told me the screwdriver method.

 

But these seem to have flared and serrated lock type washers attached to them...I see what you mean by wrong type of bolt, the bolts I have don't have the flared nut like these I ordered...

 

It's possible your flex plate is cracked at this point.
Swap the proper bolts in and see. Look for fine cracks at the bolt hole locations while you're down there.

No regular bolts and lock washers. Bolt, flat washer, and locktite, OK.
Lock washers are too small.
Careful what you read on the internet.
Just like what I'm writing here.

 

It's possible your flex plate is cracked at this point.
Swap the proper bolts in and see. Look for fine cracks at the bolt hole locations while you're down there.

No regular bolts and lock washers. Bolt, flat washer, and locktite, OK.
Lock washers are too small.
Careful what you read on the internet.
Just like what I'm writing here.

 

If you have a T350C,you should be using a metric size bolt for the converter not a 3/8 like your Moroso part number.Maybe you should check again.

 

I definitely have a th-350c.. so the th350 used standard size bolts, while the th350C used metric ?

 

Damn...

 

Friggen metric.

 

From the Pro-King Transmissions website for TH350C TC... says bolt size is 10mm x 1.5 thread..

 

So can I use the Moroso 3/8-16 in bolts in place of the M10-1.5 bolts ?

 

No


...

 

"The 3/8 -16 bolt will thread in the 10mm x 1.5 but the 10 x 1.5 bolt will not fit the 3/8"

Guy says here a 3/8-16 bolt will fit a M10-1.5 bolt hole, but a M10 1.5 bolt will not fit into a 3/8-16 bolt hole...

If this is true, these 3/8-16 Moroso bolts should fit my TH350C TC bolt holes...

 

Read the top of that chart.

 

Math.....
Assuming 0.000 tolerances in mean/major thread diameter at 75 percent engagement.
10mm=.393
3/8=.375
.018 difference

Pitch
16tpi is .0625/inch
1.5mm TPI .059/inch
.003 differance


A loose fit at best. Will not accept full torque and will have a much better chance of vibrating loose.

Don't do it. Not worth tearing up stuff when the local hardware has what you need for $5.

 

Math.....
Assuming 0.000 tolerances in mean/major thread diameter at 75 percent engagement.
10mm=.393
3/8=.375
.018 difference

Pitch
16tpi is .0625/inch
1.5mm TPI .059/inch
.003 differance


A loose fit at best. Will not accept full torque and will have a much better chance of vibrating loose.

Don't do it. Not worth tearing up stuff when the local hardware has what you need for $5.

You're right, I should do it with the correct bolts.

Those M10x1.5 bolts at the hardware store, they come with the serrated flanged heads too ?

Grade 5 or 8 ?

 

At Home Depot and Lowes, they only offer 12mm and 16mm in length for their 10 x 1.5 bolts...no 15mm in length unless it's online and doesn't arrive until the 20th.

 

Why don’t you try a local trans shop, they should have some,if you can’t wait.
Best to use the proper hardware.

 

10x1.25 not 10x1.5.

 

The thread size metric on the torque converter is : 10mm x 1.5

3/8 bolt is not the same as 10mm. They do not interchange.

If too long of bolt is used on lockup converter, you can damage the surface where if the bolt contacts the front on the converter surface. That flat surface is for the converter clutch application.

 

The 10 1.5 is for converter with the mounting nuts attached.

 

I got these...blue loctite already on them.

 

Looks good.

 

OK, before I start taking out the wrong bolts and replacing them with these new bolts, is there a torque sequence I need to know about when putting the new bolts in, or just take out the old bolts one at a time and replace one bolt at a time ?

How much torque should I tighten these bolts to ?

 

I pulled 2 of 3 of those bolts. 1 was a flanged bolt and it was tight, but I'm sure it's a 3/8 because my 15mm socket didn't fit the hex head like it does for the metric bolts.

No cracks around the bolt hole

I only had 1 bolt that was crooked, and the metric bolt went in also crooked...the TC bolt hole threads are messed up and need tapped.

 

Am I better off tapping and straightening out that bolt hole with the transmission still connected to the engine, or disconnecting and pushing the transmission back to replace the flywheel and torque converter altogether ?

 

1986 specifies a 10mm x 1.5 bolt no nut. Torque spec 40 lbs.

The 3/8x24 is for a nut in pre 1982 models. Torque spec 35 ft lbs.

Some models of TH350 and the TH400 use a 7/16x20. Torque spec. 45 ft lbs

If the converter uses a captured nut the bolt needs to match what the converter has on it. If bolts weren’t supplied then you’ll either have to buy what is recommended or figure it out.

Sounds like somebody eff’ed up.

Given these are high grade bolts I don’t think you have the joy of rethreading a captured nut into something else. Sounds like new flexplate time.

Youre experiencing what undertrained mechanics can do to a car, they're everywhere out there.

Bogie

 

Sounds like new flexplate time.

Just a new flexplate, or a new flexplate and torque converter ?

Is the crooked bolts being caused by the threads in the captured nuts or from the flexplate being uneven/bent ?

How do I check for an uneven or bent flexplate ?

Will the transmission need to be removed completely or just pushed back, to replace the flywheel ?

 

Well, aside from tightening down the torque converter bolts, I had a starter bolt that wasn't the original and was about a half inch too long, so I installed the right bolt.

My exhaust manifold bolts were also loose. I never retightened them after the camshaft break in, and from what I'm told, the bolts will loosen up over time due to heat expansion.

Tightened everything up and the rattling quietened a lot.

 

Sorry that should be converter not flexplate, brain fart on my part.

The bolt that goes crooked is going into a cross-threaded reciever. It’s possible to rethread but the ability to pull the needed torque is iffy in that the threads are likely fractured at their root and could pull out as torque loads are applied.

Bogie