Author Topic: Compression  (Read 2472 times)

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Offline ed

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Compression
« on: February 04, 2012, 03:06:34 pm »
Hi, 1st post here. I have a number of the Mcculloch models, 1010 Pro Mac 650, 700 and 800 series, several of each in some cases. I have noticed a variation in compression from 110 to 165. Three 650's all have 150+ PSI. One 700 @ 115 but runs suprisingly well. A"Pristine" 700 @ only 135. (Maybe not broken in?) I recently saw a saw on ebay referencing 180!! Holy Crud. What is normal when new? What would the minimum be in you opinions....Any easy ways to increase? I cleaned the decomp valve on one saw and it went up 35 psi....Others? Thanks..ed

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Offline man of stihl

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Re: Compression
« Reply #1 on: February 04, 2012, 05:30:47 pm »
Not all saws are the same when it comes to compression, I'm not real sure where the Mcculloch's are. I have some 10-10's and they are around 140 psi. Some of the older saws i hear can run on lower compression. Now modern saw's like a newer Husqvarna 372 can have only 135 and broke in around 145 or so. and they run great!. where if a Stihl 440 had only 140 psi, it would be time to rering it. My 440 has 175psi right now and its not broke in yet. Al Smith from this site can lell you where the Mccullochs should be. I do not know a whole lot about them. Oh yeah, I have a couple ported GTG\race saws that have 200+ psi. ;) I gain compression on saws by tightning the squish and new rings. (If wore out).
Ron

Offline Al Smith

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Re: Compression
« Reply #2 on: February 04, 2012, 07:12:21 pm »
Al Smith really can't tell you for sure how much they should have .I've never taken a comp reading on any of the Macs .

I have a 125 that I resleeved and as of yet doubt it's got over 1 hour running time .That engine is 123 cc and without using the decomp is almost impossible to pull over .This praticular one mentioned has not seated the rings yet and as such can be rolled without the decomp .Once that old dog is running it cuts just about as good as another I have which is well seated .

Some of them will surprise you .It may be the fact that on a 2 cycle the rings tend to tighten up under power .That's about the only thing I can come up with because I honestly don't know .

Now on those PM 650's which is a later version of a PM 610 they had thin rings which probabley accounts for the higher static compression readings .

Offline ed

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Re: Compression
« Reply #3 on: February 05, 2012, 09:24:20 am »
"It may be the fact that on a 2 cycle the rings tend to tighten up under power" I did not know that. Maybe I'll do a hot / cold comparison just for curiosity. Not the same as "under power" though. Hey, I have a 805 "The Professional" Is this an uncommon saw? I haven't ever seen another one. I picked it up local here in Phoenix..... ed

Offline Cut4fun .

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Re: Compression
« Reply #4 on: February 05, 2012, 11:18:02 am »
You can use search to find things or click on each board to see what is posted in them.

This 805? 

http://chainsawrepair.createaforum.com/mcculloch/pro-mac-805/
REDNECK Saw Repair Getter Done

Offline nmurph

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Re: Compression
« Reply #5 on: February 06, 2012, 10:44:56 am »
I have a near-new 700 with only 135psi compression. I have never run it much and thought there might be a problem, but it appears that might not be the case.

Offline Al Smith

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Re: Compression
« Reply #6 on: February 06, 2012, 06:38:40 pm »
I doubt it will be a problem .Most likely the difference between static and dynamic compression will more than make up for it . Anyway the proof is in the pudding so to speak .If it runs okay under power it's obviously fine .

Offline David Young

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Re: Compression
« Reply #7 on: February 06, 2012, 10:01:38 pm »
one variable that will cause a large disparity in static compression  is oil.  Another is the temperature of the motor.

 the most consistent is warm recently run on good mix. 

you want a bragging psi pour a tablespoon of 30 wt down the spark plug hole.

d

Offline Al Smith

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Re: Compression
« Reply #8 on: February 07, 2012, 03:07:10 pm »
I dunno . Some of them will pump up by  just sucking some fuel . Fact I've got an SP 81 Mac that will snap back on you every bit as hard as an 084 Stihl and that's saying something . Geeze it isn't any wonder I can about predict the weather by how bad my left hand feels in the morning .Thank heavens it passes though .

 

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