Im trying to put these bolts in right now on the big block. If the transmission were ½" lower the bolts would go in, or if the engine were ½ higher they would also. I have a TH350 Transmission going behind this big block so I first though that this converter might not fit, they make 10" ones for the TH350's right? And 400's have 11" converters, but 11" might even be too large. So Im wondering if I should pop out the tranny mount and see if it drops a hair or 2.... or do i need a different size converter? So basically its the stock 454 flexplate and the stock converter TH350, shouldnt it line up?

the tranny is located by large dowel pins on the back of the block. you can't change the position of it relative to the engine. What you probably actually have is mis-match between the diameters of the bolt circles on the flexplate and converter. what you need to do first is turn the engine a little. Many flexplates have two sets of holes in them, yours probably does too. So, you need to turn the engine without turning the converter, about 1/6 0f a turn. You'll most likely find another bolt hole that does line up correctly. Tip: don't tighten any of the bolts till you have all three in. Also, converter bolts are a high-grade bolt, not a regular 3/8" bolt like in the intake or something. Make sure you've got the right ones, they're real short too.

Tom

I bought the correct ARP bolts. I did notice there were more than 1 set of holes on the flexplate, I turned it to all the holes and none of them lined up. I'll give it another go though. I used energy susp. tall chevelle motor mounts. I didnt change the chassis mounts though. Would that do this?

Yeah it's a no go, its barely a ½" I need to get them in, no holes will go, I turned it many times. Im thinking either to hook back up the cherry picker, pull the motor mounts, raise the engine a couple hairs and bolt it up, then drop it back down and put the mount bolts back through.

The engine height will have no difference on the mating of the transmission to the engine. As previously stated by Tom

".... the tranny is located by large dowel pins on the back of the block. you can't change the position of it relative to the engine. What you probably actually have is mis-match between the diameters of the bolt circles on the flexplate and converter.... "

We assume you still have the dowel pins on your block?

I know it might seem like a lot more work, but I'd suggest putting the tranny and engine together outside of the car and using the cherry picker to drop them both in together. On both my brother and my friend's car this is how we did it. It was infinately easier than when we dropped the 350 into my Chevelle with the tranny still inside the car.

It sounds weird, but it's been easier for us to drop them in together.

if its a 1/2" on the bottom then turn 180 and still 1/2" on top then you have wrong parts...............
shane

Ive turned this thing around 360 a couple times not once did any holes line up, always a hair under ½" I agree it being easier to assemble the transmission and engine together then install. The only thing I can think of is the chassis mounts for the engine may be higher for a big block, and those need replacing. Actually I see what your saying, if I did that it would just bring the tranny up also, AND the torque converter because it connects the same way no matter what... well crap. So a new torque converter?

I agree, it might sound like a pain, but it would probably be worth it to get it out of the car and have a good look at it. As far as raising or lowering anything, like the others have said, it just wont work. If you put in the dowels and bolt the tranny up to the engine, thats where it is. If the bolts for the converter line up, than they dont. Youve gotta find out where the mismatch is. And if you do raise or lower anything and bolt up the converter correctly, all your fasteners and dowels will be off and they wont fit correctly. And, if the bolt circle is entirely different(which is the likely case) if you did raise it up and get that first bolt it, youd only get that one in. The others will still be off due to the difference in diameter.

Is there anything I should or can do before I pull the engine back out? I am guessing I need a different size converter. I knew something wouldnt go smoothly today smile.gif

drop the transmission or pull the motor and get a flexplate that has holes for both bolt patterns.

It's unlikely that you need another converter. Which part is the one you haven't used before? Is the converter new or is the flexplate new?

If you've used the converter before with your small block, then your converter isn't the problem. Your flexplate is the one that's wrong for some reason.

If you've used the flexplate before and this is a new converter THEN your converter is the problem.

If they're both new, maybe they're both wrong, LOL.

phil if you have the trans bolted to the block and two sets of holes in the flex plate then the converter shold bolt to one of the sets of holes. mark R

Hopefully its not the smallblock converter and its externally balanced.

Phil,
Where did you get the converter and the Flex Plate? I think that you have the correct parts. A small block or big block flexplate would bolt up to any converter for a TH350 or TH400. Did the converter go fully onto the TH350, 3 distinct clunks while pushing, wiggling and rotating it? You can feel each step. They often feel like they are seated when they aren't really. 10in. or 11in. makes no difference on the converter. It's where the converter bolt tabs are located. I'm confused by your post, is the tranny bolted to the engine now?. If all of the above is correct then you will have about 1/8in. or less between the converter tabs and the flexplate holes. The way you talk about about moving the engine or tranny it sounds like they aren't bolted together.
I always put my engine and tranny in seperately. First I drop the engine in and bolt up the mounts. I get the engine almost level, a couple degrees lower in the rear. I keep the engine hooked to the cherry picker for support. I put the tranny on a roller floor jack with a piece of wood under the pan.Position the jack in line with the tranny lengthwise so you can roll the tranny toward or away from the engine. Raise or lower the engine and tranny as necessary to line up the bell housing and bolt it up.It's easier to do than it is to type it up. Then you rotate the flexplate and bolt it up.

They're definately bolted together, the tranny and engine. The Flexplate came with this engine which is a 1990 454 out of a truck. The Converter is bone stock and so is the TH350 as far as I know, which was run on my small block w/ no problems. So im not sure what to do, regardless the engine will def. have to be pulled back out because there is no way these bolt holes will line up. :confused:

Hmmm, this doesn't make sense. The flexplate is a stock 454 piece, so that definately shouldn't be the issue. I've never heard of a smallblock/bigblock convertor, I always though they were all the same. Also, the X" number on the converter shouldn't matter. I think these define some internal dimension for the converter, no the external dimensions, at least that's how it was explained to me.

Sounds like the flexplate does not have the dual bolt pattern. I ran into this a few months ago on a pioneer replacement flexplate. It had two sets of bolt holes, but they were both the large pattern and would not line up with the convertor bolt holes.

The original TH350s used a smaller convertor bolt pattern than TH400s. Since yours is a 90 model and the 350 has not been built for years, GM may not be putting the small pattern holes in production flexplates anymore.

Ok, phew. Well this held me back from getting lots of fun goodies put on today, I will pull the motor tomorrow. I MIGHT get flack for this idea but it seems do-able to me. What if I take out the engine and pull off the flexplate. Weld out the holes and re-drill new ones that line up correctly. Wouldnt that be alright? Either that or a new flexplate. I wouldnt mind some welding though....

Thanks for all the posts guys...

Don't try cutting holes in the flexplate. That can really cause problems, vibration and worn pump bushings to start. Hit the parts store and find the correct flexplate. Also, don't be surprised if you run into starter issues also.
Jay

Well not cutting, Id do a clean weld and get rid of the exsisting holes and just drill new ones. But if it's still a bad idea i'll just pick up a new one. What do I look for?

Most aftermarket are drilled with the dual bolt pattern,,shouldnt set ya back too much,SFI approved are slightly higher... Do not attempt to drill new holes yourself.

Sounds good, looks like ive got my monday project laid out. I had everything balanced, if I get a new flexplate should I take it in or wiegh it myself?

You might have to weigh it again to be safe...

There are more holes than just two......


Here was my problem when I put a TH350 into my car. The engine had a 153tooth flexplate... the converter the tranny shop gave me wouldn't bolt up. I needed the 168tooth flexplate to fit it.

My new PDQ converter, fit the 168tooth wheel aswell..

You could probably just take both plates to your machine shop and have the new one made to work like the old one. I know, more money.....sucks huh?

Are starters the same for BBC and SBC? Ive heard yes and ive always heard people say no. Do all starters work with different tooth flexplates? I bought a 72' Chevelle BBC starter, flexplates are also the same for big and small blocks right? other than the mounting holes.... ?

There are starters for the 153 tooth flexplate and starters for the 168 flexplate.

You need a flexplate for a 454..period

http://store.summitracing.com/partdetail.asp?part=SUM%2DG102SFI&N=4294925134+4294863762&autoview=sku

its also a dual bolt pattern so most aftermarket convertors will bolt right up.

Starter should interchange.

That one looks good to me, cheap too. I got my old one off already. Only took about 40 minutes to lift it up and pull it off smile.gif

Whats the difference between an internally and externally balanced flexplate? Could I use either?

The difference is just what they sound like. One flexplate is for an externally balanced motor. The other you use if you internally balance the motor. Did you have the machine shop do any balancing?

http://store.summitracing.com/default.asp?Ntt=454+flexplate&x=0&y=0&Ntk=KeywordSearch&DDS=1&searchinresults=false&N=0&target=egnsearch.asp

This is the same one isnt it? Except non-sfi?

Yeah I had the whole assembly balanced. Pretty sure its all external. It's a 1990 block, GEN IV

If it was externally balanced then you have to get an externally balanced flexplate, because that is where the balancing is done. Otherwise you're going to have crazy-bad harmonics I would guess. You will probably have to have the rotating assembly balanced again, but maybe just the flexplate. But I'd ask a machinist that one.

not sure if this link will work but what about this one?

http://www.partsamerica.com/PartDetails.asp?SourceArea=&SourcePage=SEARCHRESULTS&MfrCode=PIO&MfrPartNumber=FRA100&PartType=267&PTSet=A
#Pioneer Products FRA100
Actually this thing doesnt come with the weight. ?

It's for a 72 Chevelle 454
I was thinking about taking my old one in and lining up the holes. It looks pretty similar but I dont know without seeing, unless you guys know right off.

Was there a specific model or year that these flexplates came on without the different pattern? Or was the pattern always the same? I know I can just get the multi hole ones but im curious about the bolt patterns also.

Phil,if you stop overthinking everything and get the one from the link I posted for you,you'll be all set smile.gif

Originally posted by mr 4 speed:
Phil,if you stop overthinking everything and get the one from the link I posted for you,you'll be all set smile.gif like the old nike commercial, JUST DO IT!!! smile.gif

Phil,
Do yourself a favor. Buy the one mr 4 speed posted. It is what you need. When you put it on your engine make sure that it bolts evenly against the crank flange so you don't end up with run out on the ring gear.Do you have the pin in your crank to line up the flex plate properly.If not make sure that the extra hole in the flex plate lines up with the extra hole in the crank flange. It guarantees that the weight is in the correct place. You really shouldn't have to rebalance anything.

The balance shops usually will make balance adjustments on the crank itself, leaving the balancer and flywheel "stock" balance, that way if you ever need to replace one it does not make your engine all out of balance just because your starter eats up your flywheel someday. But the only way to know for sure is to talk to the shop who balanced it.

phil If the engine was balanced why not get a crank and bolt your flex plate on then lay the conv into the crank mark the holes very carefully then drill them. Mark

I cant lay it on the crank, the engine is still in and basically installed, I just pulled it up enough to get the flexplate off. Everyone said that would be a bad idea, I was going to at first. But hey 45 bucks and im set i guess, im getting a new one tomorrow...

Guess what....there are actually three bolt patters for converter/flexplate assemblies. I went through this problem when I went from a small block/th350 setup to a big block with the same transmission. I had planned to use my 10" converter from my small block and I had bought a new flexplate for my big block with a dual bolt pattern. But my converter pattern was smaller than the smallest flexplate pattern. so I bought a new converter. I couldnt find a flexplate with a small enough pattern for the converter I had. Maybe you can though.

What did you end up doing? Thats not good to hear! I was going to order this:

http://store.summitracing.com/default.asp?target=partdetail.asp&part=SUM%2DG102SFI&N=4294925134+4294863762&autoview=sku

Are you guys sure I shouldnt just weld out and redrill the holes? I dont want to get this in the mail and have it not fit.

Well I found a flexplate identical to the B&M 20233 SFI one, which has a dual bolt pattern. Its made by Transtar, and its local, I'll try this and see what happens. I wish I was home, I thought my flexplate had dual bolt pattern also but it was a no go.