Mcculloch sp125/101b kart saw build thread

[jacob j.]

Nice work Mr. N! I think I'm going to do something similar and then use a different reed material.

 

[Al Smith]

It seems to me McCulloch have had bad runs of plating issues over the years .I don't know the actual problem was but perhaps the quality of the hard chrome .Never the less what to do to salvage them ? There's always the option of an iron sleeve liner . WTH I did it using home made tooling and it worked out just fine . Matter of fact in the last few days the subject came up on two other forums with other saw engines .I'm a firm believer anything made with human hands can be duplicated or repaired but sometimes you have to think outside of the box so to speak

 

[Al Smith]

You always have options .To replate for repairs or build a custom engine you first need to find some place to do it .Brown's in Ky used to but I think they are out of business .US Chrome perhaps ?
I used grade 50 cast iron which is what Harley used for cylinders .Nodular iron which was used for Ford iron blocks is probably better but is harder to machine and finish .You could also 4140 steel tubing which is used for aircraft piston engine cylinders .
Hart's automotive machine shop in Cecil Ohio ,one of the best in the USA if not the world uses precision honed tubing which is available in many sizes but rather costly .Weather LA sleeve would have something that would work I have no idea ,they might .Falicon ,famous for crankshafts moved from Florida to someplace near Cleveland I think used to advertise doing sleeved cylinders so that could be another option .

 

[Bigmac]

So I did some measurements, wheeled a few blocks and came up with some info the kart 101b has an exhaust duration of around 180-183ish it looks like the sp125c is about 177 on the exhaust, about .030 of an inch lower, the cp is way low, at least the one I have, it’s in that 165-166 range, and almost .080 lower than the 125c. Trying to decide how far to
Go on the cp.

 

[Al Smith]

I think no matter how you slice it it still comes back to port time area open .You could drive yourself insane trying to figure it out .

 

[Scott Kelsey]

Can you guys tell me a source for the lower rod to crank needle bearings for the SP125C? Thanks.

 

[Lee H]

Terry Ives is where i have bought many sets. I have also reused many. Are yours bad?
If there is no pitting or discoloration from heat you can probably reuse them.

 

[Bigmac]

Got some stuff done for the weekend, did some porting, nothing crazy, lifted the exhaust 1mm and radius the hard edges. Got a really nice squarish port, a bit wider than stock. Happy with it.
Also ground on stock the intake so the manual oiler still works!!!


Some pics of the stock intake vs the custom v4, still going to trim the reed stops on the v4. You can see how plugged the stock stops are

 

[Bigmac]

Also got the linkage setup on the wb

 

[Bigmac]

With some major help form @jacob j. We have some decent exhaust duration numbers for the 125cc macs some interesting results!
101b 179.2°
Sp125c 174.2°
Ported cp125 169.2° was shooting for 170°
Early 797 boost port 166°
Cp125 early 164°
Early sp125 iron liner 153.3°

 

[jacob j.]

Also got the linkage setup on the wbView attachment 318704View attachment 318705View attachment 318706View attachment 318707View attachment 318708

With those pictures, it's easy to see why the kart guys radius everything inside the block. I've seen some blocks from the long time racers that look like works of art - custom oversized heads, custom manifolds, etc.

 

[Bigmac]

With those pictures, it's easy to see why the kart guys radius everything inside the block. I've seen some blocks from the long time racers that look like works of art - custom oversized heads, custom manifolds, etc.

It I had endless time and money I would try a bunch of things, more epoxy, more grinding! Would be a lot of fun!

 

[Lee H]

Nice job, And your right " If we only had time" We could play with these things forever.

How much compression do you think you will lose with the 1mm off the roof of the exhaust port.

Is @Definitive Dave working on pistons for the 125 with Wiseco. Be nice to see a pop up piston.

 

[Al Smith]

Unless I'm mistaken back in the glory days either Wiseco or Horstman did make over bores for 101's .According to what has been said Wiseco will make anything to want but you have to buy like a dozen of them .

 

[Bigmac]

Nice job, And your right " If we only had time" We could play with these things forever.

How much compression do you think you will lose with the 1mm off the roof of the exhaust port.

Is @Definitive Dave working on pistons for the 125 with Wiseco. Be nice to see a pop up piston.

I am expecting to lose 15 pounds give or take 5 psi. I want to turn some decent rpm, so I am not too worried, I am shooting for 9500-10000 rpm. A pop up, or an optional tall piston for the saw blocks would be nice. The squish on the cp is huge! A tall piston would really help. And it would open the door for porting, I realize that’s a super small market. A standard pop up would be killer, with the aggressive porting of the 125c it would rival kart performance.

 

[Bigmac]

Unless I'm mistaken back in the glory days either Wiseco or Horstman did make over bores for 101's .According to what has been said Wiseco will make anything to want but you have to buy like a dozen of them .

Have seen the old wiesco’s for sale, think @jacob j. has had some. I believe they were cast not forged like modern wiesco’s
And yes they will make custom pistons, but it’s kinda expensive and in quantity, I have no idea on the minimum order would be money wise.

 

[Al Smith]

I've told the story a zillion times but once again Louis B who is one day older than me and we went to apprenticeship school together was number 2 nation wide in the AGKA in the 70's .He ran 101's and has his port maps ,notes etc .He was trying to locate a 101 for me but about two years had a stroke . I should see how he's doing just haven't taken the time to .Kenny Burden RIP was number 1 two or three years in a row earlier running Mc 10's .I know his entire family .I now wish I'd talked more with him . He is in the Talladega hall of fame .

 

[qurotro]

May I join the club? Just got it a few days ago. Read all threads nothing but good, however this saw is as old as my father, I might have some stupid question later on..

 

[Lee H]

Welcome to the Mcculloch 123cc club, Looks like you found a nice CP125S, Ask any questions you like.
There are a few of us here that have been in these saws many times.

 

[Al Smith]

Since at one time Wiseco did make racing pistons for the 101's and others it would make sense they still have the specs .As such since the methods have changed and likely are cut on CNC machinery it shouldn't be a big deal to write a program to do it .Back in the glory days of two cycle karting it was standard practice to rebuild the engines at around a time period of around ten feature races Which would be less than 2 hours of actual run time .Unless I'm mistaken they made them in 2 thou overbore up to around 100 thou over .