Mcculloch sp125/101b kart saw build thread

[ManiacalMark]

@Bigmac id love to see what your different saws do on a dyno

 

[Bigmac]

@Bigmac id love to see what your different saws do on a dyno

It would be interesting for sure! I am liking this 101aa more and more, it has really good torque, and I think it’s going to get a little stronger with some more brake in. And the 101d with the v4 reeds an wb is fun, have never ran less than a 50” bar on that combo, so it’s hard to say, it has port work, but stock timing. It would fun to know and see how they do, don’t think it would be crazy, just fun to know.

it would be cool to see a stock 797, super 797, cp125 sp125 , Sp125c, 797/101 and sp125/101 just to see the differences.
I am going to put together a stock port 101 wb swap soon, might put the cp stuff before I start making manifolds, want to see if it had more torque than the ported 101wb

 

[ManiacalMark]

I thought that one with the 50” bar then 36” that saw shows it has the power and rpm across the board.

 

[Scott Kelsey]

Did some digging into the 101 I purchased a bit ago. Here is the crank journal. It is pitted badly. I have an extra crank that mic's out well, is straight, and has no pitting but I am curious has anyone ever had or know of a shop that would repair, weld, and grind a crankshaft such as the 101?

 

[Bigmac]

Did some digging into the 101 I purchased a bit ago. Here is the crank journal. It is pitted badly. I have an extra crank that mic's out well, is straight, and has no pitting but I am curious has anyone ever had or know of a shop that would repair, weld, and grind a crankshaft such as the 101?

I have not, if there was my cp125 would love a stroker! Lol

 

[Bigmac]

Just as an update on the cp, did a compression test on the cp when fist assembled and after some run in, it’s the same 120-125psi with my 2 gage average, thought my gages took a dump, but tested two fresh huskies at 160psi so it probably accurate. Disappointed on the comp, but kinda impressed with the low comp cp. so lifting the exhaust may have been a huge mistake. May never know! Lol

a stroker would tighten the squish, an bump the comp, the cp has bad squish, think it could take a 4mm stroker

piston and cylinder look brand new

 

[qurotro]

Hm.. My thinking is grind the crank and refresh the rod end then fit bigger bearing pins? That sounds doable.

 

[jacob j.]

piston and cylinder look brand new

It's probably the same difference I've found with static vs. dynamic compression on some of these saws.

I have a couple of SP saws that don't make much static compression, but they're very strong in the cut, two of the strongest saws I have.

 

[sawfun]

It's probably the same difference I've found with static vs. dynamic compression on some of these saws.

I have a couple of SP saws that don't make much static compression, but they're very strong in the cut, two of the strongest saws I have.

This is very true, the old L88 427 Chevy with 12:1 static ratio compression, would often yield 90 lbs on a gauge. The cam timing would cause this. Maybe the port timing on the CP is effecting the reading?

And we used to have machine shops that would weld crank journals. Sadly those shops have closed and the old boys who ran them are mostly gone. Getting the tempering correct on some cranks was an art. Most just welded them and regrouped them. I had the nose on a very expensive top fuel motor welded. The guy just ran beads and turned it down afterward, as I watched. This was common for stroking small amounts.

 

[Bigmac]

Not sure on this cp, I wish it had more static comp and dynamic. Guess that’s the big benefit of the kart motor. I think the cp came with less Calculated compression for sure and bigger squish, that’s killing it for sure, port timing is now a little higher than the 797, but only a hair, and still less than a 125c, the chamber kinda sucks on the cp, probably why it likes more timing.

The port timing is similar to cam timing, overlap and higher exhaust ports bleed compression, with the cp it’s like they they reduced calculated compression ratio, by increasing squish area. So if calculated compression is down, then so is running compression. I was hoping I could get a taller piston for this saw, it would help a lot, would have to do more porting to compensate, but it would be interesting.

I think the 125c and the intake would be a good combo. Still going to try it on a stock port kart motor next.
Welded up and reground crank would be cool, and a stroker crank would be fun to play with too. An undersized grind with largest bearings would be interesting too!

 

[sawfun]

If you want more static, add material to the top of the piston or the chamber? Too much static is gonna be hard on the starter. It also could make it just plain hard to start. I had an early CR500 that had that very issue. That's why Honda went to a relief slot in 87, the 85 & 86's were MFers to try and start. You have to be able to spin it fast enough to light it.

 

[Maintenance Chief]

Yeah I think I'd ask Shaun if he could weld a pop up on that piston.

 

[Lee H]

Yeah I think I'd ask Shaun if he could weld a pop up on that piston.

That is easy to do then machine it in a lathe, I talked to a guy a few years ago that modded 797's
and he had pieces made that fit in the combustion chamber. He screwed and glued them in.

 

[Lee H]

Back to compression, The last 797 i did didn't have what it should have. I related it to a leaking
decomp pin or valve, replaced the block in it with one from a known member of this group and
it now runs like it should just needs more time on it to break it in. but with the original build it
pulled over hard like it had normal compression but just didn't have what it needed.

 

[jacob j.]

Yeah I think I'd ask Shaun if he could weld a pop up on that piston.

That's my plan on my next SP build - get a slug made up and then do some port work to match.

 

[Bigmac]

That is easy to do then machine it in a lathe, I talked to a guy a few years ago that modded 797's
and he had pieces made that fit in the combustion chamber. He screwed and glued them in.

That was the original plan, and why I wanted to build the cp, terry was going to screw in a combustion chamber insert, but it didn’t happen.
I did a pressure vac test on the cp, mainly to test the dsp valve, so I feel pretty good about that not leaking, I just think the cp is low to start with. But have only tested 2 at 150psi.

 

[Bigmac]

Yeah I think I'd ask Shaun if he could weld a pop up on that piston.

That's my plan on my next SP build - get a slug made up and then do some port work to match.

Considering where things are, I think I will do that!

 

[Bigmac]

If you want more static, add material to the top of the piston or the chamber? Too much static is gonna be hard on the starter. It also could make it just plain hard to start. I had an early CR500 that had that very issue. That's why Honda went to a relief slot in 87, the 85 & 86's were MFers to try and start. You have to be able to spin it fast enough to light it.

I am extremely familiar with cr500’s have had 85,86,87 and several 89-01, the other weak points to the 500 was ignition, adding a modern ignition makes a huge difference, or take the 87+ ignition and adding dual source coils and doubling the spark voltage.
If I could get the cp to 180-200psi I think it will still start ok, one of my kart motors has 235 psi on the gage, it still starts ok

 

[Lee H]

I have or had several SP125's with 180 psi comp on my snap on gauge, Never had one
as low as 120 unless it had a damaged piston.

I think raising the exhaust port really hurt it, JMO

 

[Bigmac]

I have or had several SP125's with 180 psi comp on my snap on gauge, Never had one
as low as 120 unless it had a damaged piston.

I think raising the exhaust port really hurt it, JMO

I agree I lost comp moding the port! I can see 30 psi at a max, I have an sp125c that has 175psi and it’s exhaust port is higher than the cp. the ported cp is only.020 higher than a 797. The kart exhaust is 2.5mm higher than the cp. Just surprised it that low. What do your 797 supers and cp gage at.
I am actually pretty happy with how it runs concerning. Some more comp will help torque for sure.