Twisted Up 56 Mirrometer 660 Jug Build.

[drf256]

We need more build threads here, period.

This may be an epic fail, but the work is worth it to further our knowledge/passion for these pieces of lawn equipment we hold so dear.

It’s for my pal @MustangMike , so it’s worth the effort and likely embarrassment. So here it goes...

 

[drf256]

Big block 66’s suffer from lack of transfer area to feed the increased swept volume.

Finger ports are a way of adding transfer area to a big bore, but the stock ring pins are in the way and the casting is even thinner than the oem 54mm are. One can flip the piston pins to the exhaust side, but it limits the width the exhaust can be taken to. Losing the bottom ring can allow one to assynetrically widen the exhaust port, but the factory skirts are only about 60% of the bore on the standard B.B. slug.

A 395 piston is 56mm. It’s skirts are much wider than a standard BB slug, at almost 69% of bore width. The ring pins have a perfect location, about 4mm off centerline over the intake port. But the piston is .150 taller than the BB piston. It’s got a bigger pin, but the smaller bearing allows it to fit the small rod end of the 660 rod. The skirts are much much longer than the BB slug.

Despite its heavier and better design, the 395 piston only weighs 9 grams more than the B.B. casting with the pin and bearing. With machine work only to the 395 slug, I’m at 4 grams weight above the B.B. slug with machine work only.

 

[drf256]

Here’s the 395 piston stock vs the B.B. slug.

 

[drf256]

So I did this...

 

[drf256]

After I removed .110 from the skirts and .025 from the crown. Maintained crown to first land thickness of .103.

The minimum crown thickness is .130.

You can see the ring pins in the photo. Unfortunately, the lower pin is in the intake port at BDC, so I’ll have to run a top ring only.

 

[drf256]

Had to make a spacer plate for this build. It’s .065 aluminum. With 2 gaskets plus the plate, I’m at .115 height.

 

[drf256]

Some more piston shots. You can see how much sturdier and supportive the skirts and ribs are.

Also, some rough layout lines of the skirts on the jug with more tha, .100 on each side for safety. The stock B.B. slug was nearly at port edges.

The line in the center of the intake port is the top ring pin location.

 

[drf256]

 

[Backtroller]

Got to love a build thread.....especially one that's outside of the box. Very cool. Can't wait to see more.

 

[drf256]

 

[drf256]

Ok, for you number geeks (like me), this is where I’m at. Gotta run into work for a few hours, so more to follow this afternoon.

Unfortunately, I don’t have a saw to mount this to. No time to run it anyway, so it will make its debut on Friday Nov 3 when Mustang gets here.

Here’s the data so far.

395 Piston
Starting weight 132 grams. Now 127 grams. Stock B.B. piston 123 grams
.025 off crown
.110 off skirt
.130 nominal crown thickness
.103 crown to ring land

Jug
No work
With .115 of spacer beneath
Ex roof 100*
Intake floor 79*
Uppers 126*

Squish presently -.026

So 46 from band will yield .020 squish

Gonna trim skirt a drop more to move intake to 82*

There is no freeporting, yet.

 

[drf256]

Got these supplies from @Definitive Dave who is the man, in case you don’t know that already.

 

[rattler]

Doc a big Thanks for doing this build thread I hang on every word of these kinds of builds. Great work also.

 

[drf256]

Thank you Mike. We need more build threads here. I don’t care if I’m criticized on every step, as long as it’s constructive.

 

[rattler]

Yes Sir agreed same here.

 

[paragonbuilder]

Ok, for you number geeks (like me), this is where I’m at. Gotta run into work for a few hours, so more to follow this afternoon.

Unfortunately, I don’t have a saw to mount this to. No time to run it anyway, so it will make its debut on Friday Nov 3 when Mustang gets here.

Here’s the data so far.

395 Piston
Starting weight 132 grams. Now 127 grams. Stock B.B. piston 123 grams
.025 off crown
.110 off skirt
.130 nominal crown thickness
.103 crown to ring land

Jug
No work
With .115 of spacer beneath
Ex roof 100*
Intake floor 79*
Uppers 126*

Squish presently -.026

So 46 from band will yield .020 squish

Gonna trim skirt a drop more to move intake to 82*

There is no freeporting, yet.

Doc do you know the stroke and rod length?

 

[paragonbuilder]

Also we've talked A,B,C piston and cylinder matches in the past. When using a completely different piston, I'm curious what you have for clearance?

 

[TreeLife]

Thank you Mike. We need more build threads here. I don’t care if I’m criticized on every step, as long as it’s constructive.

I live for build threads...I just really enjoy the process, the art of grinding, the purpose of the porting etc.

 

[David Young]

So what's in store for the little transfers?

 

[Fruecrue]

What up with the squish band?