1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

[bryanwess2000]

I'm rebuilding a 91 merc 3 cylinder with 3.375 bore. I wanted to know the specs for the crankshaft journals and connecting rod bearing surfaces. Also the max wear tolerance and max egg( out of round ). Information not in factory service manual. thanks.

 

[carholme]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

The OOR is found as .003" on page 4A-18. As far as journals and rods the only limits appear to be found on 4A-22/23 and it states that any imperfections which cannot be cleaned up with crocus cloth are cause for rejection of the component Understandable for the material hardness in use today. You are not going to clean up much with crocus cloth which is a pretty fine limitation in itself.

Gerry

 

[Faztbullet]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Measure cylinder bore inside diameter (with an inside micrometer) of each cylinder, as shown below.
Check for tapered, out-of-round (?eggshaped?) and oversize bore.

If a cylinder bore is tapered, out-of-round or worn more than 0.003 in. (0.076mm) from standard ?Cylinder Block Finish Hone? diameter (refer to chart below), it will be necessary to rebore that cylinder(s) to designated oversize bore and install oversize piston(s) and piston rings during reassembly.
NOTE: The weight of an oversize piston is approximately the same as a standard size piston; therefore, it is not necessary to rebore all cylinders in a block just because one cylinder requires reboring.
IMPORTANT: Ports must be deburred after honing. Measure the old pistons to see if usable,
MEASURING PISTON SKIRT
Measure piston skirt at right angle (90) to piston pin centerline, 0.50 in. (12.7mm) up from bottom edge of
skirt..50 in.(12.7mm)

PISTON SIZE PISTON SKIRT DIAMETER CYLINDER BORE FINISH HONE
Standard..................3.371 in.(85.623mm)..................3.375 in.(85.725mm)
Piston
.015 in....................3.386 in. (86.004mm)..................3.390 in.(86.106mm)
(0.381mm)
Oversize
CYLINDER BORE SIZE
Piston Size Cylinder Block Finish Hone
Standard Diameter 3.375 in.
(85.725mm)
.015 Oversize 3.390 in.
(86.106mm)
.030 Oversize 3.405 in.
(86.487m
Top bearing roller journal is 1.625
Center main journal is 1.432
Connecting rod journal is 2.22
Bottom ball bearing journal is 1.384
Connecting rod wrist pin is .956
Connecting rod crank end is 1.734

 

[bryanwess2000]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Thanks guys, yea carholme I saw the specs for the cylinder and I oversized the bores .015 and .030. I just didn't see any specs for the crankshaft. Thanks fazt for posting the specs for the journals, that's what I needed. Do you have the spec for the crank journal for the connecting rod surface, it mics 1.4175?

 

[carholme]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Faztbullet;

Many thanks for providing that information. Is this from a specific overhaul manual?

Gerry

 

[Faztbullet]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Do you have the spec for the crank journal for the connecting rod surface, it mics 1.4175?

Take your connecting rod measurment of 1.734 and measure and subtract rod needle bearing o.d from it. This will give you journal
size +/- .003

Many thanks for providing that information. Is this from a specific overhaul manual?

It is from factory technicians manual....

 

[stovepipe66]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Measure cylinder bore inside diameter (with an inside micrometer) of each cylinder, as shown below.
Check for tapered, out-of-round (?eggshaped?) and oversize bore.
View attachment 134766
If a cylinder bore is tapered, out-of-round or worn more than 0.003 in. (0.076mm) from standard ?Cylinder Block Finish Hone? diameter (refer to chart below), it will be necessary to rebore that cylinder(s) to designated oversize bore and install oversize piston(s) and piston rings during reassembly.
NOTE: The weight of an oversize piston is approximately the same as a standard size piston; therefore, it is not necessary to rebore all cylinders in a block just because one cylinder requires reboring.
IMPORTANT: Ports must be deburred after honing. Measure the old pistons to see if usable,
MEASURING PISTON SKIRT
Measure piston skirt at right angle (90) to piston pin centerline, 0.50 in. (12.7mm) up from bottom edge of
skirt..50 in.(12.7mm)

PISTON SIZE PISTON SKIRT DIAMETER CYLINDER BORE FINISH HONE
Standard..................3.371 in.(85.623mm)..................3.375 in.(85.725mm)
Piston
.015 in....................3.386 in. (86.004mm)..................3.390 in.(86.106mm)
(0.381mm)
Oversize
CYLINDER BORE SIZE
Piston Size Cylinder Block Finish Hone
Standard Diameter 3.375 in.
(85.725mm)
.015 Oversize 3.390 in.
(86.106mm)
.030 Oversize 3.405 in.
(86.487m
Top bearing roller journal is 1.625
Center main journal is 1.432
Connecting rod journal is 2.22
Bottom ball bearing journal is 1.384
Connecting rod wrist pin is .956
Connecting rod crank end is 1.734

I know this is an old topic. Is this the same specs as a 100hp in regards to crankshaft measurements I know that the stroke is shorter in the 90hp but was wondering if that was the only difference I also know it's has 3 cylinders compared to four. Or if you can find the specs for the same year but only a 100/115hp outboard. Thanks in advance

 

[Faztbullet]

Re: 1991 mercury 90hp specs and wear tolerance for crankshaft and connecting rods?

Is this the same specs as a 100hp in regards to crankshaft measurements

Yep......

I know that the stroke is shorter in the 90hp but was wondering if that was the only difference I also know it's has 3 cylinders compared to four.

Bore and stroke are the same(3.38x2.65 )