TOPIC: J blocks ??????

i've heard of the J block in line 6's but i just got a 2cyl 200 20hp with a J on the block is there a difference in it as opposed to the regular 200 20hp block.

Can't beleive nobody knows anything.

Hi Dave,
For whatever it's worth:
So I can tell you after scruitinizing and measuring the highly sought after "J" block 6 inline it's not the block that makes a "J" . I measured the port size and heights on 5 regular 1500 blocks and a J and could not find any decernible difference, the block castings are also the exact same. The difference (I believe) is that the rotating components are better weight matched and are special selected at assembly for higher RPM use. I remember
people taliking about the "Saturday" motors where parts were specially selected when the regular assembly line would not be disturbed. I have never found any speed difference between a J
and a standard 1500. Only when low dome pistons are used vs.
high domes.
I have indirectly confirmed this with a guy who worked in Oshkosh as a machinist at Merc during the hey day of the inline 1500's who said they all got machined on the same line and were
not stamped at that point.
My guess is the same holds true for a J in the two cyl, I'll bet it denotes better balancing rather than a port difference,
probably destined for an early 70's 25SS application.
Both the 1500 XS and the 25 SS were done for Stock race
classes so Merc couldn't mess with porting but they could pick better balance which generally frees up a little power, once assembled it was stamped to denote the better balance.
The switchbox & carb jetting allowed for higher RPM on the 1500 XS.
Randy

thanks for the info it will be going on a 25SS it will be a spare.

I understood the porting was slightly different on the 1500XS J block? I have read many times that they were good for a 'true' 150-155hp. Of course living in England I will never know for sure!

well then.....you should pack it all up and just move here.
OK I am going to go have my coffee now.

Thanks for that Jim! Oh & it would have to be tea !

I have both 1500's a standard and a J. I dont think I will brave the exhaust cover bolts just to measure the ports But I have heard for years that the 1500J had different exhaust port timing.

Conrad

As I said earlier I have measured these and there is no measurable difference, if there is it is VERY small. What I have heard/read is that the short shaft tuner did a slightly better job at scavanging the exhaust out, like a better set of headers would do.
Randy

Not to hijack or anything, but it that your Switzer?

Nice boat.

Yup, tis mine. It's a 69 Shooting Star...good eye! Motor is a 76 XS with a Super Speedmaster lower unit. I restored the package but kept as much original as possible on the interior, instruments, gel coat etc. Lower edges of stringers were rotted so it all came out, it's all good now. Transom was built up at the factory and had aluminum plates and flat steel braces to support the top from flexing, I replaced the braces with stainless turn buckles which work better and give more room for the tanks, battery and trim pump in the back. Does about 84 mph @ 6500 rpm on a good day. It will only go straight, and needs about a mile or so to get to top speed, it has near zero ability to turn but, that is not the point . It's an adreniline rush that lasts all day.
I threw the picture in to show I really do play with XS Mercs and have spent many hours with the both the J blocks and regular 1500's.
I run a "regular" 1500 on a restored 74 Hydrostream Vector.
Randy