TH350/348 converter clearance.

[348sedan]

I have a 348 W block with a TH350. The combination was on the road and drove perfectly. Whilst the car was apart I had the trans rebuilt and then it was re-installed with the existing(almost new) B&M converter. The converter went in fine and the mounting pads sit just over an inch down into the bellhousing from the face.(Two others I've looked at recently measured the same though one of the large trans shops has a list on the internet that shows 1 1/8"?) If you bolt the box to the engine the converter can be spun freely but there is very little clearance between the pads and the flex plate mounting faces, probably only 1/16". I'm used to seeing about 1/8" clearance here on small blocks. Obviously I realise that the clearance is pulled together when the converter bolts are tightened but it's niggling at me! When I measure the rear face of the engine block depth to the flex plate mountings I get just over 1". On a small block sat in the workshop I have 7/8". Will this small clearance cause any pump issues with the box? As I say the converter can be spun freely with the box bolted up tight it's just that the clearance seems a little tight to what I am used to. Does a 348 flex plate normally sit a little further back than a small block one?
Out of interest if the converter does not drop down that last click into the pump does anybody know what the depth from the face of the trans to a converter mounting pad would be?

 

[coogan]

If it drove fine before , why are you worried now ? What was the gap when you disassembled it ? Are you sure the convertor is burried in the lugs as far as it can go ? Maybe ask the tranny shop if there is any reason for less clearance.

 

[348sedan]

It's a questioning mind I guess. To be honest it wasn't noticed when it came apart as my brother dismantled it. As I said the converter sits just over an inch into the box and feels fully seated so I'm pretty confident with that. What is niggling at me is the distance from block mounting face to flex plate pads on the 348 being a fraction over 1" and on the small block sitting in my garage that same distance measures at 7/8". So, if I took the box and converter exactly as is and bolted them to the small block I would have the normal 3/16" + clearance before tightening the converter bolts.
If the engine and box were out of the car I would have a good measure up and see exactly why there is a slight difference but I thought I would ask others before going further. As the converter spins freely I am sure that it can all be bolted tight and will be fine but that enquiring mind wants to know what is happening.

 

[coogan]

I've got a th350 out on the floor with a stock convertor and it's about 1 inch from the bolt pad to the face of the bell housing but when I took it apart it had 1/8 clearance. At some point I'll be putting it behind a 409 so I wonder if I'll have the same issue ?

 

[poison ivy]

does the hub on converter have clearance in the crank, do you have old converter to check?.

 

[348sedan]

Thanks guys. The converter came in the car as a good running driver and everything worked perfectly. The whole running combination was taken out and then used for my sedan. The previous owner is a good friend and he had fitted the B&M converter when the package was in his car but never noticed the clearance, he can't remember what it was. I only had the trans rebuilt because the car was apart and it made sense to do it now. Converter spins freely and clears crank hub. Closer inspection however has revealed the difference. The flex plate has a slight dish backwards, enough to put the converter mount pads 1/8" further back than the sfi one on my small block. This accounts for the difference. When the box was out we inspected the flex plate for cracks but never noticed the slight dish. It runs true and even and the dish is even across the diameter so does not look like damage.