Performance upgrades for Mariner 175

[69bcuda408]

Just pulled apart my '96 Mariner 175 (carbed).
#4 piston busted, all others looks fine. Plastic oil pump gear drive on crank Scr*wed up. Cylinder walls looks good (since removing aluminum from #4) and ball honing 320 grit.
Need advice on upgrades. will run 95 octane (probably premix).

Considering sps rod bolts, metal cage rod bearings, performance reeds, exhaust tuner, velocity stacks, milled heads, SS prop, raised motor etc.

Any suggestions greatly appreciated.
(Boat: seapro 210cc).

[Bayou Native]

Do some research on here, there is plenty info. You will not get bored! Some of these guys almost know what they're talking about ;-)

[johnboy 88 vegas]

I know someone who had the same boat/ motor setup and have ridden in the boat quite a few times. IMHO a 2.5 just doesn't have the torque to push that kind of load efficiently. The upgrades you mentioned will probably get you 1-3 mph if anything so don't expect much return from the investment. The rod bolts, bearings, and plastic reeds are good for reliability but the heads are not. Setup would be your best option to gain any speed with the motor you have. A 3 liter would be much happier pushing that kind of boat if you want speed and reliability.

[David]

Bass and Walleye Boats, April 1996, yes I have too much junk in my basement...

175 Merc on a Skeeter
Land and Sea dyno
stock 166 HP, 1400 feet elevation, 65.7 mph
35 cc heads, 177 HP, 66.9 mph
Tuner(don't read this Raceman!) 191 HP, no speed listed
Reed case ported, Boyeson reeds, 194 HP (only 3 HP more peak, but broader power curve)

Final speed 70.2 and they thought there was more there.

Each modification done sequentially

[TEXAS20225]

David i still have nearly all my issues for 8 years worth of it also(so its cool )from very first issue on

[TEXAS20225]

me being i motor rebuilder (25/30 a year) i can truthfully say i have had zero positive results on reusing s cylinder that stuck a piston and i reused it without boring it out but that just my experience

[ChrisCarsonMarine]

A ball hone will make an egg shaped cylinder look beautiful,and leave it egg shaped.As Texas said,honing is often not the answer,unless the hole only had a little aluminum transfer.Be sure to have it checked with a bore guage,much more accurate than an eyeommeter.Our reeds will help,good luck with your project,Chris

[69bcuda408]

Will check bore dimensions (and out of roundness) on all cylinders. What tolerances are there for the cylinders? Tempted to just replace the one bad piston and put new rings on all others.
(I removed the aluminum from the cylinder using Muriatic acid

).

Reg. tuner should I just shorten the stock tuner or go with a Bridgeport or aftermarket one? Will tuner mods affect carb jetting?
And reg. premix: is 50:1 OK (maybe richer during ring break-in)?

[69bcuda408]

Update on clearances (after ball-honing): Cylinders 1-3,5,6 had 0.0090-0.0098 piston clearance (thrust direction) with 0.0008-0.0012 taper/out of round. Cylinder 4 slightly tapered had 0.015 theoretical piston clearance at the top with gradually reducing clearance to about 0.0098 at the bottom with 0.0020 worst case out of round. BUT since I measured piston clearance at the lower part of the skirt and that the lower end of the skirt never sees the top of the cylinder, I might not experiance too much piston slap? Tempted to skip boring, just re-ring. Please Advice.

[rock]

The advice is already there and I agree with it. Normal clearance is about .007. From the Merc service manual, if a cylinder bore is tapered, out-of-round, or worn more than .006, re-bore to .015 over. You can just hone and re-ring and it will run but it will not be all it can be nor will it likely last as long. It's all up to a guy's budget. If you are doing this yourself, see if you can rent or borrow a rigid hone. It will show you where you are losing contact.

Rock

[mouse4x4]

me being i motor rebuilder (25/30 a year) i can truthfully say i have had zero positive results on reusing s cylinder that stuck a piston and i reused it without boring it out but that just my experience

well not saying you have not had bad luck with it but i have only rebuilt two outboard motors in my life both were steel sleeve 2.5 with gouded pistons in them removed aluminum with muratic acid ran a ridgid hone through all the cylinders replaced bad holes with new pistons an re rung other holes an they both still run like a champ to this day. but niether engine was fully locked up could still turn them over.