Proposed FAQ on Mercruiser leg ID (feedback pls).

[achris]

Any comments, modifications are welcome.<br /><br />Identifying Mercruiser stern drive units.<br /><br />Here are some ways to identify the year range and type of dog clutch type Mercruiser stern drive units. This does not relate to type II, III, any of the TR series or Bravo series legs. <br /><br />All information is from Mercruiser Service training manual 1993 and various other Mercruiser service manuals.<br /><br />-----------------------------------------------------------------------------------------------------------<br /><br />The ‘MC-1’ was first used in 1967 on the 120hp package (GM 153 cu in) and ran through to 1982. From 1968 the MC-1 leg was used with GM and Ford engines up to 260hp.<br /><br />In 1983 Mercruiser redesigned the leg, gave it some stronger gears and bearings and called it ‘R’. They was used on in-line 4, in-line 6, V6 and SBC V8’s, up to 260hp.<br /><br />1985 saw a major redesign, ‘MR’, before the ‘Alpha One’ was released the next year (1986). <br /><br />The Alpha One was superseded by the ‘Alpha One Generation II’ in 1992 and has been current since.<br /><br />Some distinguishing features of various legs is as follows.<br /><br />The gimbal ring has the trim senders mounted on it from 1973 on.<br /><br />1983 and newer had a flat top cover, squared off anti-cav plate and 1½” trim cylinders. Up to 1982 had the rounded top cover, with a lifting eye, rounded anti-cav plate and 1” trim cylinders.<br /><br />The MC-1 and R legs have a preload pin in the top end of the drive shaft and the MR and Alpha Ones have no preload pin.<br /><br />The Gen II legs look a bit different. They are held together by 4 nuts and bolts, clearly visible, whereas the MC-1 to Alpha One have 5 nuts on the ends of studs that can’t easily be seen from the outside. Also the water pump on the Gen II is the ‘low pressure, high volume type’ (longer, softer blades) with a stainless steel housing whereas the earlier legs had high pressure, low volume type pumps (shorter, stiffer blades) with the plastic housing.<br /><br />Most parts, (housings, gearsets and bearings), on the 1967 to 1991 legs (MC-1, R, MR, Alpha One) are interchangeable. This includes using, for example, an MC-1 driveshaft housing (upper) with an MR gear housing (lower), or a MR driveshaft housing on an Alpha One gear housing.<br /><br />Very few Gen II major parts are interchangeable with ‘pre-Gen II’ parts. Some of the smaller things have remained the same. For example, most of the seals, the top bearing yoke and uni-joints are the same.

 

[achris]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

anyone?

 

[qystan]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

I think this is great info. Like to add this bit on the trim cylinders.<br /><br />There are 2 trim cylinders in use, one is longer that the other by about an inch and identified by the -1 in the casting number. The downtrim hoses and must match the trim cylinder. The casting number is found on the inside face of the cylinder body (the side facing the drive).<br /><br />Posn Short Cylinder Hose<br />Port 98703 99903<br />Stbd 98704 99904<br /><br />Posn Long Cylinder Hose<br />Port 98703-1 99903-1<br />Stbd 98704-1 99904-1

 

[achris]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

Qystan,<br /><br />There are 4 different trim cylinders! I'll do some reseach and add that to the article. <br /><br />Good suggestion.<br /><br />Thanks,<br /><br />Chris................

 

[Bondo]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

That's a Really Good start..........<br /><br />How about some Photos.............. <br /><br />And more on the various interchanges that Work......<br />Rather than the swaps that Just Fit.......<br />Input shaft length issues......<br />Spline count issues.....Well, in the older Mod.1s anyway......

 

[achris]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

OK all,<br /><br />How does this look?<br /><br />Bondo, I don't have the references for spline counts, this would be mainly the E-Z shift and the legs on the old Renault engines, so would you be able to do something for that section? Oh, and you got a picture. <br /><br />And a section on trim rams for you Qystan.<br /><br />----------<br /><br /><br />Identifying Mercruiser stern drive units.<br /><br />Here are some ways to identify the year range and type of dog clutch type Mercruiser stern drive units. This does not relate to type II, III, any of the TR series or Bravo series legs. <br /><br />All information is from Mercruiser Service training manual 1993 and various other Mercruiser service manuals.<br /><br />-----------------------------------------------------------------------------------------------------------<br /><br />The ‘MC-1’ was first used in 1967 on the 120hp package (GM 153 cu in) and ran through to 1982. From 1968 all GM and Ford engines up to were used with the MC-1 leg.<br /><br />In 1983 Mercruiser redesigned the leg, gave it some stronger gears and bearings and called it ‘R’. That was used on all 4, 6 and SBC V8’s, up to 260hp.<br /><br />1985 saw a major redesign, ‘MR’, before the ‘Alpha One’ was released the next year (1986). <br /><br />The Alpha One was superseded by the ‘Alpha One Generation II’ in 1992 and has been current since.<br /><br />Some distinguishing features of various legs are as follows.<br /><br />If the gimbal ring has the trim senders mounted on it then it’s 1973 or later.<br /><br />1983 and newer had a flat top cover, squared off anti-cav plate and 1 ½” trim cylinders. Up to 1982 had the rounded top cover, with a lifting hole, rounded cav plate and 1” trim cylinders. As shown in this picture.<br /><br />

<br /><br />The MC-1 and R legs have a load pin in the top end of the drive shaft and the MR and Alpha Ones have no pin.<br /><br />The Gen II legs look a bit different. They are held together by 4 nuts and bolts, clearly visible, whereas the MC-1 to Alpha One have 5 nuts on the ends of studs that can’t easily be seen from the outside. Also the water pump on the Gen II is the ‘low pressure, high volume type’ (longer, softer blades) with a stainless steel housing whereas the earlier legs had high pressure, low volume type pumps (shorter, stiffer blades) with the plastic housing.<br /><br /><br />Interchangeability.<br /><br />All MC-1 to Alpha One internals and housings are interchangeable for the top box only (driveshaft housing). The lower boxes (gear housing) and internals are not interchangeable with each other, only as an assembly.<br /><br />When ordering internal parts for an MC-1 leg, some will supersede to the Alpha One Gen II (1997) part. This includes prop shafts, from 1970, which supersedes to the 1997 Gen II shaft. 1998 and later have a newer shaft. The driveshaft for MC-1 will supersede to R, and the MR will supersede to the Alpha One. The MC-1 and R have the ‘pre-load’ pin and the MR and Alpha One do not. Lower gearsets are all different.<br /><br />Some Gen II parts are interchangeable with ‘pre-Gen II’ parts. For example, most of the seals, the top bearing yoke, top gearsets and bearings, and uni-joints are the same. Housings though are very different.<br /><br /><br />Yoke (input shaft).<br /><br />The drive end of the yoke is also another area of concern. The in-line engines up to 1982 (MC-1) were shorter, at around 8”, than the early V8s or more recent yokes (R, MR, Alpha One), around 9½“. The Gen II yokes have 3 ‘O’ ring grooves, as opposed to the Alpha Ones and earlier, which has only the 2.<br /><br /><br />Trim Cylinders.<br /><br />A number of different trim cylinders have been used over the years and this is another method to help identify your leg.<br /><br />References like front, rear, port and starboard are always with relation to the boat. <br /><br />The earliest ones were just a round tube about 1” in diameter with the hydraulic lines emerging from the front end of the ram. These are referred to as ‘internal return line’. The ram itself has an inner tube. The space between the ram housing and the inner tube is the ‘return line’ for the fluid. These rams were used until about 1981 and the port and starboard rams are the same, that is, interchangeable.<br /><br />The next series of rams for 1981 and 1982, were about the same diameter (1”) but had external return lines. That is, there is a hydraulic line at the front of the ram, the same as the earlier series, but also a hard line that runs under the ram from the rear of it through a bracket, and a piece of braided, flexible line to the manifold at the bottom of the Gimbal housing. These rams are also interchangeable.<br /><br />Rams from 1983 to 1991 were similar to the 81, 82 rams but with a larger diameter, 1½”. They also had the external return lines, but the port and starboard rams are NOT interchangeable. <br /><br />From 1992 (Alpha One Gen II) the rams were no longer round, but ‘flattened’ along the bottom, to help with water deflection. They too have external return lines and are not interchangeable.<br /><br />A number of different pumps and motors were also used. The earlier ones, up to 1981 had Prestolite motors mounted on a square black metal or plastic reservoir, usually bolted to the inner transom plate on the starboard side. <br /><br />1982 and later had a mix of motors and pumps. Some had the Prestolite motor/pumps and a plastic reservoir, some an Eaton motor and an Oildyne pump.

 

[achris]

Re: Proposed FAQ on Mercruiser leg ID (feedback pls).

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