i have a mercruiser 898 (gm 305 )5.0l year is 1978 i've striped the motor but i'm not getting much help here in the uk with the sizes of pistons mains and rods can any one help i've put the info off the pistons mains and rod shells thanks
PISTONS THERE IS A 9 on th top of piston on number 234578 pistons and a 10 on 1 and 6

on the back of the mains there is a cercled B with GM 66 under that is .0006 under that is 10 77

rod big ends have an A cercled with GMM 400 then 5471139 under that at the other end of the shell is 177 08 and under that .0005
can any body help thanks

 

Not sure what you're asking about?

It's a 305. The bore is 3.736", the stroke is 3.48".

All of that stuff about the markings on the bearings and pistons that you're taking out doesn't matter, because it all goes in the trash anyway. It's meaningless at this point in its life.

Have the crank ground down by .010", buy a set of .010" undersized bearings. Have the block bored .030", buy a set of .030" oversized pistons and rings. That's about all there is left to be done, after you throw away all that old used stuff that's no good any more. You can order bearings, pistons, and rings from places like Summit www.summitracing.com or other similar suppliers, and any local machine shop with typical engine maintenance equipment can handle the machine work.

 

thanks for your help but what i'm looking for is what size is it now is it STD

the bores and crank are ok but i would like to replace the rings and shells

 

Bore is 3.736 as mentioned. I doubt they are ok. If you measure the bores they are probably "barreled" and need to be bored out to correctly seal. If you bore it out .030" you'd need 3.766" pistons and rings - more commonly referred to as ".030" over 305 pistons and rings".

Crank and rods take "STD" bearings - if you don't intend on machining that (probably needs it though!). I don't know the exact measurement of what it should be, off the top of my head. Do you have a micrometer accurate to a ten-thou? If no, it doesn't really matter eh?

 

Yes the size now is probably "standard".

Don't worry about what the absolute value of the dimensions, at the moment; the stuff is worn out. It's kind of like the markings on the bearings. They're going in the trash, so it doesn't make any difference what those markings mean.

Any competent machine shop will be able to look up all the dimensions of all the parts. You, the assembler, don't really need to worry about that, except to measure the diameter of the crank when you get it back (should be an even multiple of .010", like 2.440" for example, ± .001" or so), and measure the clearance between the piston skirts and the bore (varies from one piston type to another, but is usually in the range of .001" - .005"). They'll grind the crank down to .010" less than the original dimension, and bore the block out to .030" larger than the original diameter. You don't have to really concern yourself with what those sizes are; you don't buy parts using those numbers. All you need to know is that it's a 305, .010" under on the bearings, and .030" over on the bore. That's how catalogs list the parts.

 

thanks i'll explane a little more as every body wants me to rebore and regrind the motor has only done 120hrs from new but we had some floods here over the summer the engine was under water for 2days so i striped it to check it out everything was fine so i thought i'd replace the rings and shells i have tryed to get shells rings and gaskets here in the uk i get blank looks off most of the machine shops as this is not a (ford opel toyota ) chevy is like asking for parts for the space shutle here so i've looked on the internet for the parts but they only list std .001 .002 .0010 so on looking on backs the shells i've taken out are the numbers above i just want to find out what size they are so i can order off the internet and get it ready for summer (by the way a rebore hear for the motor is £250 $510 ) a rebuild kit is $1000 !!

 

Buy from summit racing. They ship internationally, and their prices are so low you're basically only paying the shipping (still less than $1000!).

Summit house brand gasket kits for an SBC are $30, a real steal! Summits house brand main,rod,cam bearings are ~$12/per again, a real deal. I know they stock those in .010, .020, and .030" undersize.
You should be able to get out under $100 for everything you need, then another $100 shipping and you're set.

 

i found a lot of places in the us ,but i have to find out what size they are to order them

 

Geddy, these guys have been helping me with my 305 as well and their advice has been sound. If you just want to find out what size pistons you have in it just measure them and use the numbers previously quoted. For instance.
STD= 3.736"
.010= 3.746"
.020= 3.756"
.030= 3.766"
.040= 3.776
.050= 3.786
.060= 3.796 and that is as far as you go and is my unfortuate case seen here:

That caliper you see is about $20US from harborfreight.com. Probably not the most accurate but certainly enough so to tell you what your bore size and piston sizes are.

I think what others are wondering is why you would buy new pistons if you didn't bore the engine out.

Calvin

 

THANKS FOR THE HELP GUYS
I'M ONLY WANTING THE (PISTON) RINGS MAIN SHELLS AND CON ROD SHELLS AND A GASKET SET I HAVE A NEW OIL PUMP I'M BUYING A SET OF VENIERS TOMOROW WILL POST SIZES OF PISTONS AND CRANK JOURNALS

 

i always get confused on this, but if the crank is ground down so its smaller, wouldnt you want oversize bearings to make up the space where material has been removed from the crank?

 

I guess that depends on what dimension you consider to be "under" or "over"...

Industry standard however, they're usually referred to as "undersized", because their inner diameter is smaller than stock.

 

i think i finally understand this lol. thanks

 

mesured bore and crank they are std crank rods 2.10 pistons 3.7335 already orded the parts thanks for your help is there any body who's up on ford motors can you tell me what this is and what it's from it's around 4.0 litre

 

that looks like a ford taurus SHO engine from the 90's i believe it was built by yamaha.the later 90's was a 3.4 liter (kitre) 32v v-8

 

it's dohc only been bench run but i have no ecu thats why i'm asking was a test engine at the jenson factory

 

i assume you could get a pcm from a taurus to work as well as a harness try ebay for those just be sure its for a sho not regular

 

allready bidding on a ecu but can't find a harness as yet


here's another gmc question are the 327 and the 350 the same pistons i've managed to get hold of a 350 block crank and rods it needs boreing but there are a set of 30+ 327 pistons i see they are the same bore but i can't find any more info

 

No.

They are the same bore diameter, but have different compression height (distance from wrist pin to top of piston).

All Chevy small block V8s except the 400 (262, 265, 267, 283, 302, 305, 207, 327, 350) have the same length rods; 5.7". All small block Chevy blocks are 9.025" from crank centerline to the deck, give or take a couple of .001"s.

½ of the stroke + rod length + compression height + .025" deck clearance = height of block.

327 stroke = 3.25"
350 stroke = 3.48"

327 piston compression height = 1.675"
350 piston compression height = 1.560"