Mcculloch sp125/101b kart saw build thread

[Bigmac]

I ran into some trouble when I torqued the rod bolt, had assembled with low torque to check the rotation, and it was fine, but after full torque it wants to bind a little, double checked everything and and I can’t see anything glaring I even tried some used needles to see if that was an issue, it wasn’t. So I called terry and the short of the long, I am going to ship him the motor to see if he can find out what’s wrong. He thinks it’s possibly a piston issue or bent rod.

 

[p61 western]

I ran into some trouble when I torqued the rod bolt, had assembled with low torque to check the rotation, and it was fine, but after full torque it wants to bind a little, double checked everything and and I can’t see anything glaring I even tried some used needles to see if that was an issue, it wasn’t. So I called terry and the short of the long, I am going to ship him the motor to see if he can find out what’s wrong. He thinks it’s possibly a piston issue or bent rod.

Well chit that means yours will be with mine soon lol. Sucks you had trouble with it. He has some real nice rods there fyi.

 

[Bigmac]

Well chit that means yours will be with mine soon lol. Sucks you had trouble with it. He has some real nice rods there fyi.

This one was nos, and a new piston, I’m not worried about it, it will just be a bit of a delay

 

[p61 western]

This one was nos, and a new piston, I’m not worried about it, it will just be a bit of a delayView attachment 190916View attachment 190922View attachment 190922

Did he mention the other rod? They are bad azz, and pretty fair priced.

 

[Bigmac]

Did he mention the other rod? They are bad azz, and pretty fair priced.

No he didn’t,That may not even be the problem, it’s possible even the pin boar is a little off on the piston or something like that it seem to consistently want to bind at the nine and 3 o’clock positions, I think there is something definitely misaligned somewhere

 

[jacob j.]

This one was nos, and a new piston, I’m not worried about it, it will just be a bit of a delay.

I'm assuming you dry-mated the cap to the rod before installation and made sure the uneven areas lined up (where they strike the rod after heat-treating).

It looks like a 1/2" wrist pin set-up? Sometimes on the 9/16" wrist pin set-up, the shims will bind up after assembly and you have to re-set the wrist pin.

 

[Bigmac]

I'm assuming you dry-mated the cap to the rod before installation and made sure the uneven areas lined up (where they strike the rod after heat-treating).

It looks like a 1/2" wrist pin set-up? Sometimes on the 9/16" wrist pin set-up, the shims will bind up after assembly and you have to re-set the wrist pin.

Yes I checked, and had everything all apart again, all looks good, And the cracked caps line up nice, it’s not as tight as some I have had, the cracks are flatter not as jagged as others. And the dots on the side are correct. It’s a 1/2 pin, it’s free and smooth. The odd thing is the rod tracks dead center with the cap at 30 in-lb’s when I step it up to 60 it tracks edge to edge of the crank journal, like it’s bent

 

[jacob j.]

Interesting - Is there any galling you can see on the rod journal on the crank?

 

[Bigmac]

Interesting - Is there any galling you can see on the rod journal on the crank?

The crank is in super nice shape, and measured at new specs, I came out of a runner had chrome issues, journal is smooth

 

[Bigmac]

The crank is in super nice shape, and measured at new specs, I came out of a runner had chrome issues, journal is smooth

The only other thing I can think is if the line bore is off, like the points box is misaligned.

 

[Steve]

My SteveAlerts stopped working! Had a few pages to catch up!

 

[Bigmac]

I have been spinning it repeatedly and it wants to track to the pto side, not really side to side, it’s all at the bottom of the stroke, but only once tight. It looks like the the piston might be a few thousands crooked in the bore at top dead. One side is low and the other high, the high side is the pto side, so that would probably explain that, either rod or pistons is off,

 

[Bigmac]

My SteveAlerts stopped working! Had a few pages to catch up!

Better late than never! Welcome back!

 

[Steve]

Better late than never! Welcome back!

Thanks for the warm welcome Nathan!

I really like how you did the decomp valve. I agree that if you put a huge hole in that chrome cover RPM will come out of his grave and bish slap you.

 

[Bigmac]

Thanks for the warm welcome Nathan!

I really like how you did the decomp valve. I agree that if you put a huge hole in that chrome cover RPM will come out of his grave and bish slap you.

Thanks Steve , not going to lie, it’s a pain to do! I bought a lot of 8 heads cheap on eBay, and tried it first on a junk one, it’s hard to not break fins! Once you break a fin it gets easier! Lol and if you make a mistake on the depth, you can always use a husky decomp, I did that on another one! Lol

 

[Bigmac]

As Mikes knows my other project will get some more time now that this happened , I will start a build thread later!

 

[sawfun]

As Mikes knows my other project will get some more time now that this happened , I will start a build thread later! View attachment 190986View attachment 190985

Now thats more like it. I'm curious to see how you adapt that carb to a 125 type tank.

 

[Bigmac]

I

Now thats more like it. I'm curious to see how you adapt that carb to a 125 type tank.

need to get a 90° fuel inlet, and am making an intake manifold for v4 reeds. It’s super tight!

 

[p61 western]

I

need to get a 90° fuel inlet, and am making an intake manifold for v6 reeds. It’s super tight!

Fixed

 

[Bigmac]

Fixed

If it would fit I would!! The v4 is super tight! The reeds need to fit slightly into the block, the v6 is wider than the opening in the block, so I can’t do that and run a boot, I might space the carb and see how much room I can get under the box, then it might be possible, really want to see how this runs, if its disappointing, going to start really hacking!