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Thread: Announcing the Merc 888

  1. #131
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    what rockwell do you actually need to run rollers?

  2. #132
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    Default Case hardnening

    Quote Originally Posted by Powerabout View Post
    what rockwell do you actually need to run rollers?
    Industry sources report that 60-64 Rc is used for roller bearing support today. It's entirely possible there was some degradation in location #4, as the entire rod did experience heat soak during the welding operation. Water cooling of the heat sink will improve results, so the mid-50's is likely achievable. Welded rods will be used for the prototype.

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    Default Production resumes

    After two months work constructing a customer powerhead dyno (a Stuska water brake), it's back to work on the 888.....
    A fixturing jig was machined, rods prepped, and new copper heat sinks were turned. Chris Razor did a masterful job as usual; the welded pieces are beautiful. Machining of the pivot bearing bores will be next weekend. Then it's upper links.
    Attached Images Attached Images    

  4. #134
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    Default Master rods yes!

    At last, a few hours in the shop, and voila! Today the masters, tomorrow the links. Another couple weeks and assembly is possible.....Name:  888Rod1.jpg
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  5. #135
    Team Member proprider01us's Avatar
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    Nice work Tim!!

  6. #136
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    Very nice, looking forward to every step in this process.
    Gardner Miller
    Lone Star Outboard Racing Association

    "Water is for racing. Asphalt is for the parking lot."
    Remember....Freedom isn't...."Free".......

  7. #137
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    Default Complicated!

    Amongst other projects today, a few hours were devoted to the link rods. The first is always the slowest. Hoping to fit the first production rod this week.Name:  888Rods7.jpg
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  8. #138
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    As usual, Tim, looking great. Looking forward to see and hear it run when done. You and Dick Austin are the Michigan mad machine masters. All the best on the finished project.

  9. #139
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    Looking a lot more realistic. I like the bearing, that should work a lot better. If you look at the area outside the bearing, it needs to be greater than the area of the bolts. That is because the bolts don't see cyclic loading, they are in tension all the time and the area outside the bearings are seeing a cyclic loading. Also the material that you welded on needs to be something that is really tough. Not sure what you used, but hope you've used a high strength steel for that piece. At the same time new rod might be over kill in the area around the pin because it has a much smaller hole and a good bit more material to work with. The point being that the system will fail at the weakest point, which corresponds in this case to the smallest area.

    Finally the new rod needs to be lightened as much as you can. The amount of stress in the system and the loads are due to reciprocating weight and the new rod has a lot more area than it needs. Machining the new rod into an I beam would remove a lot of weight and reduce the stress in the all of the places where the system has limited area. Also assuming that you're making the rod out of something that is really high strength, like 4130 and then heat treat it to high strength. Another way to do that would be do mill out the center of the rod and make it hollow and then cut some reliefs in the outside. Because you have access to the inside of the rod from the clevis end you do have an opportunity to structurally optimize the rod. With that in mind there's a pretty chance you could reduce the reciprocating mass a lot and still have a good cross section left that would get you closer to a system that could work to real speed as opposed to just getting to idle or mid range speed.

  10. #140
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    Default More work to go

    Quote Originally Posted by Yellowjacket View Post
    Looking a lot more realistic. I like the bearing, that should work a lot better. If you look at the area outside the bearing, it needs to be greater than the area of the bolts. That is because the bolts don't see cyclic loading, they are in tension all the time and the area outside the bearings are seeing a cyclic loading. Also the material that you welded on needs to be something that is really tough. Not sure what you used, but hope you've used a high strength steel for that piece. At the same time new rod might be over kill in the area around the pin because it has a much smaller hole and a good bit more material to work with. The point being that the system will fail at the weakest point, which corresponds in this case to the smallest area.

    Finally the new rod needs to be lightened as much as you can. The amount of stress in the system and the loads are due to reciprocating weight and the new rod has a lot more area than it needs. Machining the new rod into an I beam would remove a lot of weight and reduce the stress in the all of the places where the system has limited area. Also assuming that you're making the rod out of something that is really high strength, like 4130 and then heat treat it to high strength. Another way to do that would be do mill out the center of the rod and make it hollow and then cut some reliefs in the outside. Because you have access to the inside of the rod from the clevis end you do have an opportunity to structurally optimize the rod. With that in mind there's a pretty chance you could reduce the reciprocating mass a lot and still have a good cross section left that would get you closer to a system that could work to real speed as opposed to just getting to idle or mid range speed.
    The first production link is only about 50% machined as shown. The pivot end must be slabbed from .625" to .585" to increase clearance from the crank cheeks (.640" between cheeks). Then, the wrist pin end will be cut further to .500" to B98 bearing width. Factory .060" hardened spacers will be used; the boss spacing needs to be opened .050" to accommodate (Merc rods are .446"). The beam itself will be narrowed to appx. .550" to make clearance for the intake side piston skirt (already cut away flush with the scallop). Finally the beam section will be milled with a ball end cutter to provide a modified I-beam shape and reduce weight.

    Rods, links, and pins will be matched/balanced before the pins are tack welded in place. Alignment between blocks is critical, because Merc rods are top guided. Opposing pistons will suspend the rod/link on the crank pin, hopefully in the center, and perfectly perpendicular to the cylinder bores. BTW: Material selection is 1018 cold rolled steel. Welder Chris Razor selected a high nickel rod. Drawn cup bearings provide the hardened bearing surfaces, no heat treatment is planned.

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