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Thread: Mad EFI mid
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08-06-2022, 07:18 PM #166000 RPM
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When m a d said the power head will pull it into alignment, i just shook my head, no way. i dont think a dial indicator is the right instrument to use, reasons being, you can move the drive shaft several thousands by hand in all directions because of the distance from the lower unit top bearing. spline alignment and a bent driveshaft are separate issues. wish i had seem this thread sooner, i gotta pull it apart now.
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25two.stroke liked this post
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08-06-2022, 07:38 PM #17Member
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Wheres that engineer who’s on the Merc V6 history thread lol! I think they mentioned the OMC shafts breaking in his thread. Have to reread that part of it and what he did in it to fix the issue with merc v6. But I think your right there’s nothing holding that shaft at the upper end until you mate it in the power head even then there has to be an allowance for a little play. That is why I was saying you would have to mimic the powerhead splines and the studs to be able to bolt it all together tight with the ability to measure the top of the driveshaft and then now that I think of it some way to mearsure the middle and bottom parts of the shaft at the same time as it spins.
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08-06-2022, 07:42 PM #186000 RPM
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Mid Layout & Check
Enuf about using carpenters squares, straight edges, vernier gauges, plumb bobs and so on. Put the damn mid on a machined layout table and see if the fly cut ends are parallel to each other by a digital scan. Flatness would be a good start (daylight and 0.005 feeler gauges). Doesn't matter what the height dimension is. It will wash with the driveshaft spline end float. If the ends are canted, fly cut the ends just like you would do for an engine head. If you have the "meat" (edge margin) open up the engine stud bores to a maximum ID to "float" the engine. Make sure your studs are not chewed or galled and at MMC (Maximum material condition). Fly cutting the ends should make the engine and gearcase surfaces truly parallel to each other. Oh, and another thing, all these fasteners should be retorqued at least every 10 hours or so. Racers don't have this problem because they are constantly pulling everything apart and reassembling.
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2thelake thanked for this post25two.stroke liked this post
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08-06-2022, 07:51 PM #19
Welp, the last thing I do after cuttin, sypherin, tackin, wigglin, weldin, cursin, clippin an callin it ready to mud n paint ... is give it the clink~clunk test.
I have a hard time holdin the phone and runnin the shaft back n forth .. but ya get the idea ....
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08-06-2022, 07:56 PM #20Member
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25two.stroke, stoker2001 liked this post
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08-07-2022, 07:42 AM #21
The mid needs to be put in a mill with a dial indicator in the collet to see if the top and bottom surfaces are parallel and go from there... I have a plate made for omcs that has the powerhead bolt pattern and a hole for the drive shaft to just fit thru I have used it many times checking engines that have broken mutiple drive shafts. Looks good as always Chaz
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stoker2001 liked this post
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08-07-2022, 08:16 AM #22
Could set the mid on a piece of level glass elevated enough to put a spot line laser under the glass and broadcast the laser up through the center of the hole and measure the difference with calipers. If you cant find center make a bushing and center drill it to 1/16” or so. Just enough for the laser to shine through. Check for parallel surfaces too while your at it. I cant think of any other way to measure it although Chaz method is undisputedly excellent.
Hydrostream dreamin
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stoker2001 liked this post
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08-07-2022, 01:45 PM #23
I have a friend who has made the same thing , the same way for the last 20 years or so , tell me I will never be rich ... because I just can't leave "well enough alone" .
I rekkon he's right, but usually before I'm half done with a project, I've already deemed it inadequate and redesigned it in my head over and over ....
Building mids .. either cast factory stuff .. or the stick-mids for Gordon ... can sometimes be tough. A small tack can pull the parts over ... and into a bind. Sometimes I just have to walk away for a day to regain my sanity ... well what little I have left ..
Plates, bars, bushings, bosses, transfer dowels ... and in the end, your right ... tramming front to back ... left to right produces an exact number ...
"WARNING" I was so happy I said "biotch" in this vid ... "WARNING"
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08-08-2022, 12:16 PM #246000 RPM
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Shrink Factor
I forgot one other factor to add to this dimensional salad. Aluminum shrinks 1/4 inch per foot when cooling from molten state. Carbon and stainless steel shrinks about 3/16 inch per foot. This could be another factor which is "moving" the boss dimensions. Photos indicate that the mid casting was not adjusted for "best fit" prior to machining.
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25two.stroke, stoker2001 liked this post
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08-09-2022, 11:21 AM #25
Todd would never say let the powerhead pull the driveshaft straight .. he knows better.
As far as shrinkage goes .. I get a bit of that when it's cold .. As far as the cans go, they are cast in one state and machined in another, so I'm sure they have enough time to cool off. Temp is a valid point though. We do outboard blocks with zero deck. Car blocks (alum block - steel sleeve) get done with the sleeves proud by .005-.006 thou to allow for growth.
Lets keep in mind that there have been hundreds of these cans done , with only a few driveshaft problems. And those have been traced back to multiple other issues.
When these cans are machined, they are surfaced on both top and bottom. Then as stated, the lower yoke holes. From there , a jig is bolted up that captures top and bottom that has holes for the drill + tap pattern. Those three positions are always the same. Keep in mind these are castings, not billet parts .. so like car blocks look to be offset or core shifted ... these can look to be drilled out of square or rotated, but all the holes line up.
In reality, it's a kit. It's up to the builder to check for casting flash in the driveshaft tunnel. To see how well the hole in the adapter plate is aligned. Etc.
I have a couple ideas (can't sleep) I'll take pictures .. but now I gotta run thru the rain locker.. gotta go get a physical to see if I'm healthy enough to be put under next week for my shoulder opp. Pppfftttt .... they should have seen me in my drinkin days ..
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08-09-2022, 11:34 AM #26
I woulda hoped, but those were his words.
Yeah I figure if this is one of 500 or 1000 to have a problem then its still damn good. I know that core shift occurs in casting and how the bolt holes are aligned relative to the casting doesn't matter, its just cosmetic. What really matters is that the lower bolt pattern is aligned with the powerhead bolt pattern. This one is not. And if he expects the builder to correct a 0.009" misalignment in his cnc work then that is crazy. 0.001 or 0.002 ... maybe. But I bet you wouldn't build a mid that binds when you put the powerhead splines down to the lower, and then tell your customer its fine and you see nothing wrong.
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08-09-2022, 12:05 PM #27The Historic Photo Master
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...wondering if he has another mid he could ship you?...
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08-09-2022, 01:18 PM #28
I woulda loved that. Its not like I said he was wrong or nothing in the beginning. I just didn't get it. I did everything he said to do to just verify there was an issue and he says there's nothing wrong. So I hope he is right. I hope now that I put it all back together with a welded shaft then it will last. But I have a hard time believing it. Only time will tell. And I hope if something breaks again he mans up like I would and says yeah send it back and HE can look at it. I bet if he put it back in his jig and told the cnc to cut the top bolt pattern it would start cutting in different places that the holes are now. I think its as simple as the cnc made a mistake but Todd said quote "That would be impossible" for the cnc to make an error.
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08-09-2022, 01:38 PM #29
can you measure the offsett on your block your crankshaft socket compared to the holes!?
i am thinking the surface from the top of the can and the gearcase mating area are not completly paralel
possible solution would be install the mid plate as in the picture and redeck the gearcase mating area
now the gearcase mating area and the top of the midplate should be paralel
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08-09-2022, 02:06 PM #30
On the powerhead side the crank is perfectly centered between the studs. The red line in your drawing shows that the CL of the D.S. is 0.009" out of center for a total of 0.018 difference of measurement from the driveshaft CL to the port stud hole and to the starboard stud hole. Yes, you are right, this could be due to the top and bottom surfaces of the midsection not being parallel or a shift in the alignment of the bolt holes. I measured the adapter plate itself to verify it is still square and it is. I got the engine all assembled now and built exactly how Todd said to do it. First trial run will be this Friday.