McCulloch Chain Saws

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mogulmasher said:
I suppose the open transfers perform better? I'm guessing the bridge was added to add to piston life?
Click to expand...

I believe years back someone posted MAC literature that stated the divided transfers provided better performance. Maybe due to creating a swirling flow. I am not sure if I recall the last point correctly.

Ron
 
rwoods said:
I believe years back someone posted MAC literature that stated the divided transfers provided better performance. Maybe due to creating a swirling flow. I am not sure if I recall the last point correctly.

Ron
Click to expand...
I was just thinking the bridge would help support the rings. Sometimes when ports get too big there can be problems with rings catching.

Anyone think there is anything to gain by smoothing out the bottom edge of the transfers? I don't know if it may slow the velocity or alter port timing too much.
 
vinnywv said:
View attachment 834525
I believe i found the reason for low compression and the nasty grinding sound as i slowly turned the saw over. Backstory...i found a great looking pm805 and bought it. Yes ebay and seller said it had lots of compression. I made an offer and it shows up. 50/50 chance of a good engine from ebay. Again the rest of it looked very good. So i tried turning it over gently and it sounds like sand in the engine. So i take it apart and to my dismay i find this. The exhaust side has very little chrome left on it. Intake side is ok. The saw looks like it was barely used. Very little saw dust on it. But very little chrome. Ive got few options at this point, find a cylinder or rechrome this one. Piston is garbage also. Anyone have a good spare theyd be willing to sell? Its a q port exhaust, 82cc, drilled for decomp valve.
Click to expand...

Ouchy man. Now's your chance to weld the Q before replating:)
 
RolandM said:
Yes,
Doing this sort of thing you need a pile of parts saws to play with. Also you have to be careful, as I get onto later.
Today I ran up the PM 555 with the newly rebuilt carb. Massive improvement but still not perfect. Low screw out 1 1/2 turns and speed changes on tilting. I built this about 3 years ago, and it had a million miles on it before I got it, so time for a bit more than a blow off with the airline. Drive side seal leaking and exhaust loose. I know the seals were not changed then, and just now hardened. 5/8 X 7/8 X 1/8" for drive end with double lip ordered. The exhaust rattling - screws loosened off - but and here is the but. I noticed that compared to the 700 the 555 has less fin depth and as I had fitted the complete exhaust off a Danarm 55 there was a big gap between the cowl and the block which means cooling air has an easy route rather than being forced through the fins. This space is occupied on the 555 by the horizontal pancake style exhaust, and so a simple swap should of ended in disaster. I have got away with it. Dug out the pancake reed and will port it as best it can be whist waiting for seals. So a reminder about keeping awake with this fun.
On the Pro Mac 700 here is some intake port pic's. Extra timing comes by shortening the piston skirt, but the effort here is to try and make transition from round carb to oval intake as smooth and gradual as possible, but not make everything too big.View attachment 830121View attachment 830122

Roland.
Click to expand...


So have a bit of run time on the hot rod project 700. Had both the tweaked and standard 700's running together, and picking up in turn cut on cut to get a feel for what the result was.

To recap I have extended the intake timing to 140' of duration, tided up and blended the various steps in the intake and similar on exhaust side. No changes to transfers to exhaust timing, no other changes to the rest of the saw.

The changes are subtle, the Mac character remains. Maybe a little loss in torque right down, but difficult to be sure. No loss in the working range. Both saws running same bar length and both on 3/8 chisel chains in a slightly hungry raker state. A definite increase in top end speed. The hot rod saw runs at a guess ~500 rpm faster in its happy working spot. Idle unchanged, no spit back or oil deposit in air box. Power increase - yes. Not mind blowing, but unmistakably stronger.

I am happy - I suspect next move is exhaust on this power quest.. That outlet from the head is awkwardly tight. Not going there right now, too busy and cutting done for this season pretty much.

Last point, fuel consumption. Both tanks emptied together so no negative on the hot rod. 700's use much more fuel than my 555 which gets noticeably more work done on a tank.

Roland.
 
Maintenance supervisor said:
Alot of times I'll put a tank seal in and button everything up, then set the saw out in the blazing sun with the air cleaner cover off , that'll make it build pressure to the whole system and a mystery leak will show up pretty quickly, obviously it works better in the summer.
Click to expand...
Or just sit in the shade with a beer and a Mity-Vac and find the problem in two minutes. LOL
 
Fwiw, us chrome and millennium are the only 2 places I know of that offer cylinder replating. Those are the only 2 places I've ever had snowmobile cylinders done by, I've never had a machine shop tell me there was another option.
 
U.S. Chrome has several different locations, the one I have used is in Fond du Lac, WI.

https://www.uschrome.com/locations
The Sawzilla seal set will work on 600 Series saws and 10 Series saws with the narrow bearing where the seal fits the same bore as the bearing. The seal that fits inside the wide outer race of the other bearing has a smaller O.D., I think it is 1.375 but it has been a few weeks since I checked.

Mark
 
I spoke to bob on it. The piston would not matter due to the machining and fitment anyway. He sends them to wisconsin. He charges 225.00 plus the ride. He also has pistons for it so likely its a total of near $300.00 parts plus shipping back to my house. His pistons are either 92519 or 87791. Thats a complete piston rings and bearings. They are 65.00 dollars. So i could send it myself after i buy the parts from bob or send it to him in the first place.....easy button is to let bob have the fun. He was really excited to help on this project. Usually he tries to talk me out of spending so much on a saw. He will ask is it worth that? But this time he went through a parts list off the top of his head and told me he would be more than willing to take care of it. If it makes him happy id spend a few extra to do that.
 
vinnywv said:
I spoke to bob on it. The piston would not matter due to the machining and fitment anyway. He sends them to wisconsin. He charges 225.00 plus the ride. He also has pistons for it so likely its a total of near $300.00 parts plus shipping back to my house. His pistons are either 92519 or 87791. Thats a complete piston rings and bearings. They are 65.00 dollars. So i could send it myself after i buy the parts from bob or send it to him in the first place.....easy button is to let bob have the fun. He was really excited to help on this project. Usually he tries to talk me out of spending so much on a saw. He will ask is it worth that? But this time he went through a parts list off the top of his head and told me he would be more than willing to take care of it. If it makes him happy id spend a few extra to do that.
Click to expand...
Thats what Bob told me $300 He's good people. I would let him be the one stop shop so to speak. and Get Er Done! lol. I now have two SP81s with 120ish compression. gonna strip them down and if fixable the blocks are going to Bob. Back in the day we trashed a bunch of blocks I wish I still had to fix now.
 

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