TOPIC: 1971 Merc 1350 porting question..

Hi all,
I have started my next boat/motor Resto it's a 71 Sidewinder 16 Super and what was advertised as a 71 1150. Someone along the way had swapped on later 1150 year decals over the originals, and when looking closely I noticed faded numbers on the top cowl looked more like 1350 so I checked the S/N and it corresponds to a 1350, that's cool, I like the thought of the matching highest H.P. year correct Merc with this package.
Curious still, I thought I'd pull transfer port covers off to look at intake port size. The 1150's are pretty small height wise, relative the the higher hp porting so an easy determination and I thought best to confirm powerhead was not swapped.
What I saw surprised me, the ports are tall indicating 1350 porting rather than 1150 porting (yeah!) and skirts/rings are clean as a whistle. (yeah!) but, curiously the pistons have the power port in them. At this point, without pulling powerhead apart, I can not confirm if the cylinder walls have the power port relief in them.
Did the 71 1350 have power porting? I thought that was introduced on the 6's first on the 1500 in 73? I can't find this specific info in anything I have. I'm thinking that if they did not have power ports then a previous rebuild was done using ported pistons.
Eventually, I'll take this all apart but, wondering if someone knows the answer, It'll be a while before I get started on this and I wanna know what I am dealing with!
Thanks,
Randy

The 1970-71 1350 was the first "Direct Charge" inline 6. Not power ported.

The direct charge design replaced the conventional deflector style that the 1250 had. The direct charge piston is the same as the later power port without the power port. A power port piston is a direct replacement for these old girls.


You have possibly a 1350 block that has been rebuilt at some point and they used newer pistons. I believe at some point the power port piston would be all that merc made and that is what would have been used in it. All normal


I think the 1970-71 1150 and 1350 have the same porting if you can believe that. You have to look at the serial number on the block or the carbs to determine if its a 1350.

The 1350 serial number was stamped on the front cover by the distributor mount. Mine is there.

Yes in 1973 the power port block/piston was introduced in the 1500.

Not that you asked but some may wonder "is it a 1500 then?" NO starting in 1972 with the 1400 the mids changed to accept the dual port exhaust. No 1500 block will mount on anything earlier than 1972

The 1350 was the first block that was not named. The 1250 block prior to it was named Typhoon.

I bet you have a 1350 if I were a guessing man. It seems many times these girls were rebadged later in life to 1150.

I have two 1500 short shafts that were labeled 1150's when I got them.

I have a 1350 I need to get together someday. Wish ya luck.
Conrad

Hi Conrad,
Thanks for the reply, a source of info I trust!
Reading what you laid out puts some confidence in understanding what I have. The clamp S/N is a 1350, I'll look at the block number, thanks for telling me where to look, it could have been switched. I remembered something about Merc only offering power ported pistons at some point. I wonder what the difference is between the 1150 and the 1350 these years for the HP difference, if not porting, maybe carb CFM or reed stop height, exhaust tuning? Simlilar to the tricks on earlier 850/1000 differences? I am more familiar with the earlier mercs 69 down and the later 73 up mercs but not these transition 3 year only versions, I do know there is very limited block/midsection interchangeability but not the particulars. I'll learn now that I have one of that ilk.
Now I'll have to tear it dowm to make sure who ever was in there knew what they were doing. The pistons still appear new and are ported so some money was spent but, the spark plug wires were automotive junk, they didn't even put the threaded ends on, just stuffed it in with the conductor bent over the insulation, held in with the boot!...yikes! total hack job. Now I have visions of crossed rod caps, poor inner water jacket install or worse.
Thanks!
Randy

I wonder what the difference is between the 1150 and the 1350 these years for the HP difference,

I think its just carb size and reed stop height that made the diff. Thom knows this particular motor well if he gets on here.
Conrad

milkdud wrote:

I wonder what the difference is between the 1150 and the 1350 these years for the HP difference,

I think its just carb size and reed stop height that made the diff. Thom knows this particular motor well if he gets on here.
Conrad

Port size is the same, differences are as follows on the 1150:

-Smaller reed openings (stops);
-Larger venturis in the carbs;
-Smaller jets in the carbs.

All of the above can be changed to turn the powerhead into a 1350.

If I recall, there was a difference in design of the exhaust baffle on the earlier models, but later on they were all superceded to the same number. I doubt any differences there would be as significant as the carb and reed stop changes.

Far as the power-ported pistons go, probably at some time the motor was rebuilt and they used "holey" pistons. The extra holes would have no effect in a non-power-ported block.

One last thought, the non-tuner exhaust plates had a steel baffle and the bolts would get loose, baffle go sideways, cause big problems. If you do pull the powerhead, make sure that baffle is in good shape and the bolts are secure. Probably wouldn't be a bad idea to install new bolts with red Loctite.

1350's are strong runners, I still have fond memories of the '71 I had on a Sidewinder 16SS............ed

One last thought, the non-tuner exhaust plates had a steel baffle and the bolts would get loose, baffle go sideways, cause big problems. If you do pull the powerhead, make sure that baffle is in good shape and the bolts are secure. Probably wouldn't be a bad idea to install new bolts with red Loctite.

Mine was cracked when I took it apart.

Thom built my motor, and heres what was done, original 115, back to a 135. All said so far spot on....Ed, Conrad, and Thom know the motors well too.

"The '72 1150 is a choked down 1350 with a few flow restrictions to give the lower HP rating so Merc wouldn't have to come up with a different powerhead to fill that HP range for the consumer market.

Initially this 1150 needed a rebuild because the inner water jacket had cracked and let water into #3 which was trying to die when I rescued the beast. It still had 95 psi on #3, but the rings had started to seize and consequently had scored the bore.
I had #3 bored .015 and installed a new piston there.

I had all holes pro-honed while I was at it and mic'd for roundness, etc to insure the beast was still within factory tolerences.

The block surfaces were machined too to insure everything was flat in the water jacket areas for a correct sealing.

All other pistons were carefully inspected, mic'd, & cleaned. I replaced one standard size piston too, but (4) of the (6) original pistons went back into their original holes.

Everybody got brand new rings & needle bearings.

The crankshaft got new main bearings.

The end caps got new seals & so did the crankcase.

I installed 1500 reed blocks and reeds, which measure out the same as the original 1350 reeds.

I am installing '72 1400 carburetors - which are virtually identical to the original 1350 carbs & I am installing the original .0785main jets required for the 1350 at sea level.

The exhaust tuner plate and inner water jacket are both NOS 1350 parts that I had machined to insure they too are flat so they will seal correctly.

These modifications: Main jets, reed blocks, tuner & inner wj complete the conversion of the 1150 to a true 1350.

The only difference between the 1350 and the 1400 blocks is the 1350 had an oval tuner to the mid-section and the 1400 had the dual square port tuner to the mid-section. And,...The inner wj & tuner plate configuration changed barely.
T..."

That's all good info guys. I have later 1500/1150 reed blocks up the ying/yang and I have a lead on 1350 carbs. I'll pull powerhead and disassemble to check everything and inspect the tuner. Does this mid split in a similar way to the 1500's with the upper and lower tuner plate clamping the upper motor mounts? The tuner fastens to the lower one?
This is where this site works GREAT!
Thanks to all my in-line 6 bro's keep the info coming.
Randy

Randy, on the older models there is no split tuner plate. There is a thinner exhaust plate that sandwiches between the mid-section and the powerhead. There's a 1/4-28 bolt thru the exhaust plate at the rear, this fastens to the mid-section. The exhaust plate holds the water tube, and has a 'tuner tube' at the bottom which bolts up to the exhaust tube going to the lower unit.

The exhaust plate is basically an open plenum on pretty much all the older models except the 1150 and 1350, where that pesky baffle is mounted down the "pipe" so to speak.

From what I understand, the baffle affects exhaust tuning to give a better mid-range, I'd expect very few would ever notice if it were gone. Dunno if the small restriction of the baffle would make a difference in top end, if it were gone. You never know what those wiley Merc engineers had up there sleeve, it even make top end better too!

Here's a diagram showing the plate and associated parts:

www.boats.net/parts/search/Merc2/Mercury/1150/2836019%20THRU%203525440/BOTTOM%20COWL%20AND%20SHIFT%20LINKAGE/parts.html

The only real diff between 1150 carbs and 1350 carbs, besides the size of the main jets, is the 1150 carbs had a carb-throat venturi that was quite a bit larger in size. I'd expect that would restrict airflow to some degree.

The venturi can be replaced, so to turn 1150 carbs into carbs you can use for a 1350, just replace the main jets and swap venturis.