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That is definitely a forged piston. I forgot how bad those old "TRW" forgings looked compared to modern pistons :) I can look them up monday and see what clearance they suggest. I might have a book here at home somewhere I can look in over the weekend.
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I am almost afraid to ask what you had to pay to get those things in Mercruiser boxes :(
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I got a absolutely amazing deal on the pistons :). Sure they may be ugly but there is probably millions of merc and GM crate engines built with them and worked fine. These are going to be at tops 500hp builds, they should be fine. If I was building anymore than 500hp the whole rotating assembly would be scrapped anyways. I still fight my self on going stroker but the parts I currently have would not be enough for the cubes
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Originally Posted by Camalot
(Post 4666859)
Mercruiser where sneaky feckers in the mid 90's by branding some of their 4 barrel Carburetor engines "MAG" engines. |
Well I did a lot of digging into this and apparently those specs are correct for those pistons, .0025"-.0037" with a max of .0075". On all the hot rod forums there were a lot of guys questioning it as the instructions with their new power forged TRW's said .0015. I could see Merc wanting to open that up a little for marine use. Lot of guys said they set them up at .003" and had no problems. And yes their good up to .0075 max. Funny thing one guy said he honed an old block and put a used set in it and had .017" clearance! Said it ran fine for years! I seen those are NLA from Merc now but one place, MarineEngine.com still had a set for $200! What a steal!
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Originally Posted by picklenjim
(Post 4666895)
Well I did a lot of digging into this and apparently those specs are correct for those pistons, .0025"-.0037" with a max of .0075". On all the hot rod forums there were a lot of guys questioning it as the instructions with their new power forged TRW's said .0015. I could see Merc wanting to open that up a little for marine use. Lot of guys said they set them up at .003" and had no problems. And yes their good up to .0075 max. Funny thing one guy said he honed an old block and put a used set in it and had .017" clearance! Said it ran fine for years! I seen those are NLA from Merc now but one place, MarineEngine.com still had a set for $200! What a steal!
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Originally Posted by picklenjim
(Post 4666895)
Well I did a lot of digging into this and apparently those specs are correct for those pistons, .0025"-.0037" with a max of .0075". On all the hot rod forums there were a lot of guys questioning it as the instructions with their new power forged TRW's said .0015. I could see Merc wanting to open that up a little for marine use. Lot of guys said they set them up at .003" and had no problems. And yes their good up to .0075 max. Funny thing one guy said he honed an old block and put a used set in it and had .017" clearance! Said it ran fine for years! I seen those are NLA from Merc now but one place, MarineEngine.com still had a set for $200! What a steal!
so does .003 sound like a good place to put these? That's what I have been leaning towards thanks everyone for the effort and research. It is appreciated |
Originally Posted by Griff
(Post 4666894)
Those were the very early (late1980's) "454 magnums" that were mated to Alpha drives and were actually 330's.
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Originally Posted by regalman4925
(Post 4666908)
so does .003 sound like a good place to put these? That's what I have been leaning towards |
interesting comments here,
sorry i dont know what piston to wall clearances were set up at.on my 547s But, as others mentioned,, thats why u / i go to a good shop with experience in marine and race motors its their job to know this and advise YOU. i can stay my rods are at 2.8 thou, mains 3.5 thou |
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