Makita 6401 to 7901 Plus porting the 7900 and the Solo 681

[Mastermind]

That's a nice thread Randy, thanks for sharing. Do you think you'll have the time to record some vids from thes saws when done?

Oh yeah. We will have video.

I have a question
Wouldn't it be easier to make the base plate out of round stock instead of square? Wouldn't you be able to use a Three Jaw chuck if that all you had?

That won't work because you cannot adjust runout with a 3 jaw.

How do you decide how much to take out of the Squish Band?

Experience. I've done a **** ton of saws, and had to learn what to do to each one by trail and error.

Awesome work randy! Have your ever put the solo crank in a 7900?

No Carl. I have still got a NOS Solo 665 though. We might have to play with it someday. It's like a stroked 6400 with a closed port jug.

Is the solo rev limited just like the 7900?

Yes.

So the Dolmar uppers were just as narrow in height as the Solo ones before grinding?

Or is that your point, that smaller tighter uppers make more power?

The work is beautiful.

The whole transfer passage setup is small and tight on these saws. They make a lot of flow velocity.

I have a stock OEM 7900 jug sitting on a shelf, would You like me to snap some pictures for comparisons with the 681 jug?

Interesting thread.

Sure. I love to see these threads get more folks involved.

 

[concretegrazer]

Beautiful work sir.

The Solo has the windowed piston. I wish I had a slab sided piston.........I bet it would help.

Isn't the dolmar piston slab sided?

 

[Mastermind]

Beautiful work sir.

Isn't the dolmar piston slab sided?

The latest top ends are, and the 7910 is. These saws both come with windowed pistons (the earlier version).

 

[MillerModSaws]

The latest top ends are, and the 7910 is. These saws both come with windowed pistons (the earlier version).

If you need a slab side holar. I have a brand new saw sitting here tore apart. I'll jerk the piston and get it in the mail.

 

[Sty57]

That won't work because you cannot adjust runout with a 3 jaw.

So if a guy made a mandrel to cut the Squish band by hand, would you be able to cut the base on an 3-Jaw?

 

[Mastermind]

If you need a slab side holar. I have a brand new saw sitting here tore apart. I'll jerk the piston and get it in the mail.

I'll just have to be content with the windowed piston Carl. You know how it is.........when they are done, they're gonna leave here.

So if a guy made a mandrel to cut the Squish band by hand, would you be able to cut the base on an 3-Jaw?

That will work.

 

[sunfish]

Excellent thread, Randy!!!

 

[cgraham1]

Hi Randy.

 

[wde_1978]

Stock OEM Dolmar PS-7900 cylinder pictures Version 1!

Tried to take the pictures at a similar angle/point of view and order like Randy did.

5 Megapixel pictures taken with non-smart mobile phone Sony Ericsson Elm @ macro setup, no flash, natural outdoor light (cloud covered sky).
Pictures have been cropped (unimportant surrounding removed) but not resized - might take a moment for them to load.

 

[wde_1978]

Stock OEM Dolmar PS-7900 cylinder pictures Version 2!

8 Megapixel pictures taken with smartphone HTC One S @ macro setup, no flash, natural outdoor light (cloud covered sky).
Pictures have been cropped (unimportant surrounding removed) but not resized - might take a moment for them to load.




The HTC tended to refuse to focus on the point I wanted it to, the Sony Ericsson Elm is much easier to get a good focus on a specific spot.

 

[wde_1978]

Stock OEM Dolmar PS-7900 cylinder

A view down the barrel with the HTC One S - it seemed to like this view point!

Again 8 Megapixel pictures, macro, no flash, natural outdoor light with cloud coverage.

 

[Mastermind]

Very nice pics. The lower transfer openings are quite a lot different.

 

[wde_1978]

Very nice pics. The lower transfer openings are quite a lot different.

They seem not to be beveled much, if any!?

Looking at both mine and Your pictures of the 681, it seems as if the 681's intake is taller then on the 7900.
It also looks as if there is a difference in transfer tunnel wall thickness, might be an optical illusion though!
But one can't deny that these cylinders show striking design similarities.

Stock OEM Dolmar PS-7900 piston:



Piston ring says "MAW".

 

[Locust Cutter]

Subbed

 

[Mastermind]

I noticed that the intake was taller on the Solo. I raise the roof of the Dolmar intake about 3mm to end up about the height of the Solo's.

 

[Trx250r180]

do these saws use similar #s to a 372 ?

 

[Locust Cutter]

Sp Randy are these a customers or are you selling them?

 

[jar944]

Sure. I love to see these threads get more folks involved.

If you dont mind. a 7900 vs 7300 transfer vs a AM 7900.

 

[redfin]

I noticed that the intake was taller on the Solo. I raise the roof of the Dolmar intake about 3mm to end up about the height of the Solo's.

How much room do you have before the ring would get into the intake?

 

[mdavlee]

There's a good bit of difference in the cylinders. More than I would have thought on the intake also.