McCulloch Chain Saws

[leeha]

Lee & other Guru's:


Piston 2.292

Bore: 2.304/.305


Can I use this piston with new .020 rings?

Can I use .030 over rings and file the end gaps "to spec"?

Do I have to suck it up and go .030 over?

-Andy

minosi, Bad news.
You have .012 to .013 thou clearance.
Way to much. You should be at .004.5 to .005
It may clean up at .030 but i bet it will have
to go .040. The good is, Terry Ives in Ca. has
pistons for the 101 kart motors in every .004
increments up to .068 over. And a 101 piston
should work in your 797 as long as the rod length
and wrist pin diameter are correct.. You should
have your machine shop measure it and see where
it will clean up at. If you can find a machine shop
to bore a blind cylinder, I can help. I have a shop
40 miles from me that doe's all mine for $80.00.



Lee

 

[heimannm]

I do not have a lot of first hand experience with these bigger saws, but it sure looks to me like a +0.020" piston in a +0.030" bore comparing your figures with the charts.

If the bore is in good shape you may be O.K. with a +0.030" piston, otherwise it will be time to invest some $$ in your find to really make it a treasure.

Do not try to get by on the cheap with just a new set of rings, you will be sorry.

Mark

 

[minosi]

Thanks Guys,

Edited my post to better reflect my thoughts, I don't mind spending the money...I do want to do it right.

The bore is true, he measured it in multiple places and it's a solid number.

It's also in remarkable condition, with a light hone being enough to restore the bore. It has no damage, scuffing, scarring or otherwise.

So, go should I go with a .030 piston, or should I use one of the Ives pistons at another diameter?

I'm am green when it comes to all the boring & clearances etc. so bear with me.

-Andy

 

[heimannm]

The +0.030" piston should be PN 67093.

The cylinder and piston chart I have has two sets of dimensions listed for the same piston part number based on earlier serial numbers and later serial numbers.

Earlier numbers for the piston are 2.301/2.300 top and 2.3035/2.3025 bottom.

Later numbers for the piston are 2.303/2.302 top and 2.3055/2.3045 bottom.

According to the list I have, the largest standard bore (2.2805) and the smallest piston diameter (2.2700) would leave 0.0105" clearance where the smallest standard bore (2.2795) and the largest piston diameter (2.2735) would leave 0.006" clearance on earlier serial numbers. The chart does not give any dimensions for the 0.010, 0.020, or 0.030" over bore cylinders. If you simply took the standard bores and went 0.030 over you would get 2.3105/2.3000.

I would recheck your piston and cylinder making sure they were both at the same temperature (leave them together for 8 hours or so to make sure they are the same) and make a decision from there.

More than 0.010" does seem pretty excessive, but you would have a hard time putting a 2.3055 piston in 2.303 bore.

Mark

 

[minosi]

Thanks Mark.

So it seems going .030 over is headed the right direction.

I spoke with Terry Ives...I need to provide a wrist pin diameter for him to determine whether he has the right piston for this application.

I will probably just send Terry the piston assembly as the pin looks like it requires a proprietary puller.

My engine guy will do a blind bore for $65.00, so I look good there.

-Andy

 

[cowroy]

opcorn: I am like a sponge right now

The knowledge from you guys with these big engines amaze me. Can't wait to find one some day.

 

[minosi]

Will this piston assembly work:


Marmax's Kartsandparts.ca - vintage cz motorcycle go kart stop :: mcculloch vintage kart engines and parts :: vintage go kart mcculloch mc 125cc .030 piston fits mc 101 101a 101aa 101b 101c 101d 2.3030" 2.3030 includes rings ,piston bearings p/n


Andy

 

[mad murdock]

Thanks Lee,

I'm going to my engine guy this morning to figure this out.

The calipers should be close if not right on, it's probably the bore I measured incorrectly...don't have a good tool to measure that.

-Andy

In the aircraft world where I do my day job, we have inside mic's but don't use them much, it is real easy to misread it. Calipers, not precise enough by a long shot. We use telescoping Tee gauges and an outside mic, they aren't real expensive, but your measurments are real consisent! You want to check out of round and cylinder choke since you are that far into it, IMO. That way you have a real good grasp on overall condition. That is going to be one nice saw when you git'er done!

 

[heimannm]

That part number does not appear in the charts that I have.

It appears to me that either the wrist pin is in a different location (which would requires a different length connecting rod) or the skirt is shorter.

I don't know...

Mark

 

[heimannm]

Telescoping gauge

I was missing several telescoping gauges from my set, made a Google search, and ordered a set on line for around $70, arrived within 4 or 5 days last year.

Looking again I see HF has a 6 piece set for $14.99 + $6.99 shipping with 5 positive reviews.

You can buy the Starret set for $150 or $336 depending on who you choose to buy them from.

My micrometer came from Sears/Craftsman and has multiple anvils to adjust from 0-1" up to 4-5" if I recall correctly. I generally leave the 2-3" setup in mine and it's ready to go for most of my saw applications.

Mark

 

[minosi]

That part number does not appear in the charts that I have.

It appears to me that either the wrist pin is in a different location (which would requires a different length connecting rod) or the skirt is shorter.

I don't know...

Mark

Thanks Mark, figured I'd ask...

Andy

 

[leeha]

Will this piston assembly work:


Marmax's Kartsandparts.ca - vintage cz motorcycle go kart stop :: mcculloch vintage kart engines and parts :: vintage go kart mcculloch mc 125cc .030 piston fits mc 101 101a 101aa 101b 101c 101d 2.3030" 2.3030 includes rings ,piston bearings p/n


Andy

This piston Perry has is indeed a CP125 thick ring piston.
It can be used but will require the short connecting rod
to go with it. The 797 uses the long rod. Acording to my
Mac book the 69304 piston should mic out at 2.304.5
to 2.305 at the skirt.
Your bore dimension isn't coming out right for a stock
mac bore. Standard bore 2.280, .010 2.290, .020 2.300
and .030 2.310. Your bore is in the middle of a .020 and
.030 bore. Your block may have been improperly bored
and causing you to have excesive piston clearance.
Must have had some serious piston slap.
And your wrist pin diameter should be 1/2 inch .500 for
a standard 797.
I would go with Terry's piston once you find out what size
you need.


Lee

 

[minosi]

I would go with Terry's piston once you find out what size
you need.Lee

That does appear to be the best, and perhaps only, option.

Thanks for the explaination

Andy

 

[minosi]

"The Fire Breathing Beast" is turning the corner


Just talked with Terry, going to send my piston out to him...


I have a bunch of NOS parts coming for her too...some cosmetic, some out of necessity...she should come together nicely.


I guess the "boring" 5-10E will have to keep me pacified until everything gets here:hmm3grin2orange:


Andy

 

[fechtichmac]

pm800

New Addition
Very low used, piston etc. like out of box´´´
had missing starter pawls, may be broken but no damages inside the fan housing.
was stored not as good and with bio chain oil.But everything works as it should!
E.View attachment 282331View attachment 282332

 

[BigDaddyR]

No kidding. That is in sweet shape. Nice get!


Sent from my iPhone using My Fingers

 

[Eccentric]

New Addition
Very low used, piston etc. like out of box´´´
had missing starter pawls, may be broken but no damages inside the fan housing.
wasnt stored not as good and with bio chain oil.But everything works as it should!
E.View attachment 282331View attachment 282332

Very nice. No go forth and get a 28" bar/chain for it.

 

[fechtichmac]

Very nice. No go forth and get a 28" bar/chain for it.

I have a 28" b+c but dont dare (yet) using it since it`s NOS
Will try to order one from current production wich are still available.
View attachment 282343

 

[paccity]

puled these out last nite alittle clean up and they run pretty good for a little saw.

 

[heimannm]

Confused

I have a 7-10 that I have had for several years (thanks again to Plant Biologist for helping me secure that one) equipped with a pop up style compression release. In addition, I have 5 different IPL's, 4 of which show the same pop up style compression release.

Last week I saw two 7-10's on e-bay with the lever type compression release, both looked to be pretty good shape. I did not get the first one, I did get the second one...

It arrived on Friday and sure enough it says 7-10 on the top cover, looks to be all original, and has a 10- Serial Number. Turns out to have very good compression and started right up with some fresh fuel added. I will install a different bar and chain (came with a 16" hard nose bar) as I have a couple of the Yooper 18" bars on hand. I still need to do a little more cleaning, but this one is definitely a keeper (as if I would get rid of one in any case).

I was going to beg for a copy of the IPL (85017) but as I started looking through the ones I have, I see I already had one and hadn't noticed the lever style compression release before.

Well, I learned something this week and thought I might pass it along.

Enjoy,

Mark