Another SP-125/101b build

[cpr]

This engine was supposed to go in a 790, but didn't. To read that story go here: http://www.arboristsite.com/chainsaw/172208.htm. Rather than further clutter that one, I want to start fresh with this build.

Several guys have been down this road, Brad is doing one concurrently that I am watching quite intently and leeha and rwoods are going to be doing it very soon as well. Collectively, we stole the design of this particular installation from a 125-blocked, stock-appearing racer that mcbob has been racing in Oz for a while now. GTG special, these. Too hot for work, not fast enough to race.

I hope to document my experiences building this one, specifically what it takes to get a 101b into the SP-125 chassis, no matter what carb you use. Had I put this in the 790/5/7, it would have been a little bit easier.

My donor frame was a hybrid CP/SP125 I got off feebay last year that was supposed to be a runner, but has no compression. I haven't taken apart the CP block yet, but I'm betting I find a stock piston in a bored cylinder. I can reach in through the exhaust port and rock it back and forth. I'll save that for another day and rebuild it as the hybrid CP/SP it was.

Then the 101 itself. This one has stock ports.

The exhaust from the outside.

In through the exhaust.

Intake side transfers. The "cover" for these is the sloper intake with reeds. There is another set of 3 on the other side accessed through plugs and fed by ducting on the other side of the cylinder. In addition, there are 2 "boost ports" seen opposite the exhaust above.

Down through the top looking at the exhaust.

Down throught the top looking at the boost ports.

Out of photo capacity. More to follow.

 

[Jacob J.]

.004" over? So that must be a Burris piston? I think only Fuller and Burris made those odd sizes.

 

[blsnelling]

What carb, intake, and reed block are you going with? How about exhaust?

 

[cpr]

Barely visible in this shot is the name above the wrist pin identifying this as a Burris piston (they're still in business, but don't list any McCulloch parts on their website).

It's an odd-ball, too. .004 over.

Attached to it is an AEE H-beam rod in place of the McCulloch one.

So, that's the lay of the land. Now to get one of these in the SP-125, there is some minor block machining to do. If you've ported a saw this will be easy, just don't screw up because it'll be an expensive mistake and Jacob J., Ambull, busmech, Leeha, RandyMac, Eccentric, Heimannm, me, and a bunch of others will be lining up to whack ya one . I may get decked before this is over myself.

First thing I tackled was to get the small bumper block in at the base of the block. You can see the 2 holes where it went on the CP block at right. I measured it off and center punched the kart block for the holes. DO NOT use those 2 small holes already there. Center is closer to the bloch and more outboard.

Pilot holes drilled. I temporarily set the stuffer plate in place and a right angle manifold on the block to keep to a minimum on chips getting inside. I'll still have to flush the engine out, though.

More to come.

 

[cpr]

Done.

Next, I have to get the passage drilled for the manual oiler rod. It goes where the hole-to-nowhere is in the stuffer. I was VERY nervous when I first did this on the MC-91. I figured there was no way to fit it all in, but it works.

The oiler rod passage does slightly interfere with the chain-guard/engine mount boss, but when assembled it all works.

The next bit is going to take awhile. I have to get the rear AV mount to attach to the head. You can see the 2 holes in the shroud of the CP block where it goes and nothing on the 101 head. I'm leaning towards aluminum block on the outside (leaving the 2 gussets) and another block between fins 1 and 2 and TIG welding them in. Then drilling and tapping the mount holes and drilling out and counterboring the block between the fins for the head bolt.

I have a shopping list of small parts to get. This saw will use a BDC carb on a sloper with the bottom of the airbox cut away to fit it. For exhaust I have a GEM header that comes back and down at a 30deg. angle for now. I may change that for the "sleeper" look.

Speaking of the BDC, here it is next to an SDC20 that came in the late-model Super 797s and CP-125s. I think I figured out what the letters mean: Small Damn Carburetor and Big Damn Carburetor :tongue2:.

 

[cpr]

Lastly, my little corner where all the fun happens. It isn't the cleanest, the biggest, the brightest, or the best stocked, but I get by and enjoy how cozy it is.

 

[turtle561]

just seeing red x's on last post #5. previous ones were fine. great stuff.

 

[nmurph]

just seeing red x's on last post #5. previous ones were fine. great stuff.

Yep!

 

[Ambull]

Man that 101 fever is running rampant. Looks like you have things pretty well covered. Subscribing.

 

[cpr]

just seeing red x's on last post #5. previous ones were fine. great stuff.

On the move for the rest of the day, but it's working on my phone.

 

[Brian13]

Looking forward to watching this one. Still waiting for the methanol 101 project to.

 

[leeha]

Nice project. Will be following this thread.
Sounds like you have everything under control.





Lee

 

[heimannm]

Watching and learning...I have two MAC 10's and one MAC 40 (or vice versa, can't remember right now); I will try to slip one of those in a D-44 or Super 44 over the winter just for fun.

Mark

 

[rwoods]

:help: all the good stuff is hiding under the red X's.

Keep it coming. I'm still gathering parts. Ron

 

[rwoods]

Speaking of the BDC, here it is next to an SDC20 that came in the late-model Super 797s and CP-125s. I think I figured out what the letters mean: Small Damn Carburetor and Big Damn Carburetor :tongue2:.

I've been doing a little research on the BDC. I've read that the single pumper was designed to pump 5 gph :msp_w00t: The standard carb for the 101B was a double pumper because the engine was starved for fuel if you run alky. I don't know if mine will be too hot to work but it appears it may be too thirsty to run long. Ron

 

[cpr]

I've been doing a little research on the BDC. I've read that the single pumper was designed to pump 5 gph :msp_w00t: The standard carb for the 101B was a double pumper because the engine was starved for fuel if you run alky. I don't know if mine will be too hot to work but it appears it may be too thirsty to run long. Ron

Yeah, I'll need a 2 stage for the methanol one. I'm not opposed to using a tilly for this, but I need that top threaded hole to put some allthread in and bend it to recieve the cover.

 

[rwoods]

Some advice on cutting mag.

I am trying to split the 125 tank that Ambull gave me (don't ask why). I don't have a dremel or die cutter. A jig saw with hack blade or coarser blade barely cuts it and the cut is pretty ragged. Best results so far have been with a sawsall hack blade in a handle but still I have only cut about 6" in 45 minutes - this is killing me. Any suggestions. I'm afraid that if I continue with my current method I'll be 85 before I'm done and I'll likely break the delicate webbing at the handle. Any suggestions? Also I don't need a mag fire in the chainsaw lab (aka my basement). Thanks, Ron

 

[rwoods]

CPR, I was looking over my dis-assembled kart saw and noted for the first time that the builder took the easy way out - no fuel tank snubber and the rear av was mounted to the cowling only. You can tell the saw has been used from all the layers of sawdust and pitch I had to remove so it must have worked. Ron

 

[cpr]

After talking with a mechanic friend of mine that I trust, welding the head to receive the AV mount is out. It boils down to the melting temparatures being so different that the result is gas pockets and inclusions that lead to a very brittle weld. I'm not up for ruining this head.

I got some aluminum at the hardware store today and Saturday morning will tackle the fabricating. I'll use JB Weld to secure it. It's good to 500 F and if the head gets that hot, I have other problems. Once the holes are drilled and tapped throught the second fin, nothing's going to move anyway.

BTW, Marmax is out of the copper head gaskets. Not sure when they'll get more. I'll call RM Motorsports tomorrow. May swing in there Monday and see what else I can score...

 

[parrisw]

Nice!! Good to see threads like this popping up on here. Love it!