Yammie 50hp crankshaft rebuild question.....

[fofiveoh]

Your attachments are not opening?

I am clicking on the "insert image" button, and adding the JPG file. Its working on my computer, so I guess I am doing something wrong. sorry.

[fofiveoh]

tuna do not make HP, you can move the power band that you have by workin the tuna, short tuna will move the power band to the top of the range ( your hull will not like that) long tuna helps low and mid range of the curve. the top of the tuna where the gasket sits, there is a squeeze about 1 inch down, mill the gasket end to move the squeeze closer to the block, i've run the trumpet tuna, she ran well..........check the squish band, then cut the head, so not to pay for some thing you have to fix

This makes good sense, and I appreciate you considering my needs, not neccesarily just a racer's needs. Based on what I have read prior to this, I was all set to cut it off! Now I am going after the other end. Do you know if the stock tuner aluminum is decent for welding on?

Kinda sounds like the bevel on the exhaust ports to raise the ceiling a bit is what you are suggesting may be the best bang for the buck (free!!)? How much are we talking about beveling? Will I want to change my timing or mains with a mod like this?

[fofiveoh]

OK, so I tore in a little deeper and got the tuner out tonite. Was
planning on doing this while power head was off, but not yet.....now I got a bigger pile of stuff to clean up and put back together, shweet!!

So, the gasket end square hole is about 35mm wide, and tapers down to about 25mm or so, about 40mm deep into the hole, then starts tapering back out to the bottom of tuner. It looks like I could mill off maybe 2 mm or so before getting into gasket sealing problems, but not much more than that. Is that what you are saying? If this helps the lows and mids, does that mean high end is gonna suffer a bit? I am hoping that I end up with a little more speed in the end, as the little boat makes lots a runs about 6-8 miles. Am hoping that if I do a few other little things that get me some HP and rpms, that I will be better off across the board. Is this what you are thinking? I am prolly gonna take her to work tomorrow and get it milled,but am gonna wait to hear, since its a lot harder to put the metal back on!
Also, the transition between the tuner and the part it bolts up to is pretty good, but I see a couple ridges or steps in the hole just above the transition. Looks like they were cast in there on purpose? Wondering if I should do any porting work it this area?

Thanks a million in advance...

[Fast Fred]

what we re doin is shorting the exhaust pulse, by movin the squeeze closer, to help it scavinge harder, sooner. cut a 1mm (.040 ) bevele on the top of the exhaust, follow the oval shape, this will help it scavenge longer, and blow down a bit sooner, which will help it transfer better. an so to get more volume of mix in there( more volume of mix is what makes real hp) cut the center rib ( 2 over 2 reeds blocks as i remember ) out of the reed block, use a two stage fiber reed with a full lower reed ( so it covers the rib in the reed block. 53-54hp with cut the head. she would be stronger all a round, maybe turn 200-400 more rpms on your hull , you may want to think about traidin up........just want to be realistic

[fofiveoh]

You have been doing this for a while, haven't you! LOL
Its a nice little boat I picked up cheap for my son a while back, the poor guy I got it from had an idea that he wanted to start fishing, and bought the boat from someone who had cracked the case and patched it with Belzona. He was upside down from the beginning. Boat had a 60 on it (98 model), but when he found the case busted, he bought a used 50 (2006). He didn't know his old prop wouldn't work, the shop pulled the only prop they had on the wall that would fit the spline, he finds out the hub spun, mo money every time he turned around. Kept having troubles, jackleg mechanics cleaning his carbs, on and on. Last time it acted up, he was told CDI was bad, and he was done. He also learned that bass fishin isn't quite as easy as it seems on the tube, so he sold it cheap. Psi was 120, oil looked good, so I bought her, and spent a couple months redoing the whole thing before I ever put in in the water. Once I got her going, I learnt that she was propped so bad it wouldn't get outa water without sending kid to bow, max RPM was 3900! I am thinking that this is prolly what wore dem pistons & bearings out? New prop, shes all good fer a couple years till the kid blows her up. Didn't feel like re-powering, and I needed a new little project. I figure I will get her running in time for him to tear up da bottom end, then Ill get something else (a 70 would be great). Prolly shoulda just done that. Once she is fixed, Ill be keepin my eyes out for sure.

[fofiveoh]

Great advice, you have shared more than most will, and I really appreciate it. As I go along, I still have a million questions. Hijacked my own thread!! BTW, I was told that the unshielded bearings on the crank is gonna be OK, sure hope so. When does rev limiter kick in? Can I get to 6000-6200 without cutting the wire? That's good for me if I can even get there. ANd does anyone really break their new motors in for hours and hours, or do you think I can do it in a few heat cycles. Heres a little before and after of the boat.Attachment 59641Attachment 59642 a few more upgrades since then.

[Tiller guy]

what we re doin is shorting the exhaust pulse, by movin the squeeze closer, to help it scavinge harder, sooner. cut a 1mm (.040 ) bevele on the top of the exhaust, follow the oval shape, this will help it scavenge longer, and blow down a bit sooner, which will help it transfer better. an so to get more volume of mix in there( more volume of mix is what makes real hp) cut the center rib ( 2 over 2 reeds blocks as i remember ) out of the reed block, use a two stage fiber reed with a full lower reed ( so it covers the rib in the reed block. 53-54hp with cut the head. she would be stronger all a round, maybe turn 200-400 more rpms on your hull , you may want to think about traidin up........just want to be realistic

The squeeze your referring to is the exhaust were it gets small? My Yamaha 30hp had a bunch of casting imperfections and I removed all of them and it opened the squeeze. Did I screw up by doing that? I never thought about how that could affect the exhaust pulse.

[fofiveoh]

Fred,

Rebuild is finished, and I am really happy with the way it turned out. I did some whacking on the tuner (milled the gasket end, and I did take an inch off the other end too), did the exhaust bevel and cleanup porting, and the reed block mods, and decided that I would run it as is before milling the head. I was able to take the boat to the water for a break-in this weekend, and much to my surprise, the boat has picked up about 225-250 RPM already, and holeshot is definitely better too. I haven't done anything to the jetting, but did a couple plug chops at WOT and plugs look OK. I am just tickled so far. I still need to verify the squish, and need to check compression again after rings set in a little, but wanted to thank you for the tips!

[Fast Fred]