Turbo 44 Merc - take II

[Tim Kurcz]

Hi everybody,

Dixon Smith asked me to start a new thread on his behalf. He will populate the thread soon with images, video links, and comment. Just a reminder: He completed his first turbo 44 in 1991, and was the inspiration for my turbo 56 Johnson.

As you can imagine, reed life on the Merc reed cage was very short in this first effort - basically a teardown after every weekend. Naturally this grew old quickly, and the engine has not been run since 1994 or 1995.

Enthused with the turbo and other projects here, Dixon and long time engine building friend Greg Sands visited for help with engine planning. After looking at piles of parts, engines, and discussing many options, Dixon decided to build a hybrid turbo 44. He will pick things up from there.........

Stay tuned!

Tim

[Tim Kurcz]

Hello all,

Here's a teaser while Dixon gets his files together. Taken in 1992 or 1993, his turbo 44 Merc uses an "Aerocharger" with self contained oiling system.

Tim

[Dixon263]

This is the starting point, a 37# block of 7075 alum that I happened to have. The original front crankcase half of a 44 weighs about 3# and isn't up to doubling the horsepower without problems. The new design will solve two problems, one, the reeds will be in an area that is easily gotten to, two, the made from billet front half will be much stronger than orig. At this point, I'm actually quite far along on the project and somewhat dropped the ball on pics, but I'll try to catch up.

[Dixon263]

Here is the progress after bandsawing and milling the basic shape. At this point, the center line bore was not done yet. The machine that is pictured above is a DeVlieg jig mill that weighs in at 35,000 lbs and has a feature that will clamp the axis's that are not being moved solidly for extreme ridgidity. Up to the point of these pics, the DeVlieg hasn't yet been used, only a Hurco CNC mill for basic shape.

[Tim Kurcz]

Hey Dixon,

Looks good so far...... BTW: That's one BMF drill bit. Surely you didn't use it to cut the 1/2 crank circle! Please keep the pics coming.

Tim

[Dixon263]

Hey Dixon,

Looks good so far...... BTW: That's one BMF drill bit. Surely you didn't use it to cut the 1/2 crank circle! Please keep the pics coming.

Tim

The drill is 2 15/16" and I deceided not to use it so I milled the bulk of material out with a 3/4" ball end mill, leaving about 1/8" stock for clean-up with the boring tool (shown above). If I went with the large drill, I was afraid that deflection due too cutting only one half, may force the drill into the block.

[Fastjeff57]

May I make a stupid suggestion? Since the reeds take a pounding with a turbo (that slams them shut under intense back pressure), would it be possible to run this engine--under boost conditions only--without any reeds? The thought would be to have a by-pass arrangement that would send boost pressure to BOTH sides of the reeds when the boost is up, by-passing the reeds with the main air charge. When the boost pressure exceeds the crankcase compression, the air charge will roar right in there without need of reeds. (A GM diesel engine comes to mind here: They have a common crankcase pressurized by a blower that feeds the cylinders without any reeds at all.) To get the motor started and running off-boost, a simple, separate air flow circuit would use reeds in a conventional fashion.

Just a thought.


Jeff

[Dixon263]

Jeff, the problem with short lived reeds may be due to the original reed location being just too close to the crank throws. I just never could bring myself to close the reeds stops down to insure they wouldn't be able to open far enough to touch the crank. The broken reeds would all look the same, missing tips and split down the middle all the way back to the stops. The reeds 'see' more crankcase pressure, but the pressure is somewhat balanced out by boost pressure on the underside of the reed. On the dyno tests I did on 44's, I installed a reed on the outside of the crankcase very similar to the old days when the outside reed would pressurize the fuel tank instead of using a fuel pump. On a conventional 44, the one-way internal crankcase pressure would reach about 7 1/2 PSI. In the hydro I ran the turbo on, I had a dash mounted 25 PSI pressure gauge that, with about 12 lbs. of boost, would pin the gauge needle. I'm thinking the reeds would still be necessary at boost speeds too achieve these much higher than boost, crankcase pressures.

[Dixon263]

The pictures here show how I dealt with cutting the rod clearance into the new crankcase. I always assumed that the rod clearance was a true arc, but by cutting a scrap crankcase, I easily saw the true shape. I simply traced the sectioned crankcase on a piece of graphite, then cut the graphite to size and with an EDM (electrical discharge machine) I plunged to depth for a near perfect match. The video shows the electrode starting to cut the second pocket. Have your sound on for viewing.
http://www.youtube.com/watch?v=_ZPEp2PN8dY

[Dixon263]

This is how I went about cutting the front of the crankcase, reed cage pockets. The pic is the screen of the CNC Hurco that shows the program that was used to cut the four cavities. It's always fun and a bit scary when you have a part with alot of time into it, on the CNC when you hit "cycle start" a watch it go to work. One little error in programming really comes back to bite if things don't work out as planned! Btw, 7075 aluminum is said too be unweldable, so this adds too the stress level.
https://www.youtube.com/watch?v=knzJ...e_gdata_player