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Squish... Should I care?

wildroamer

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Hi gang,

Getting ahead of myself, but thinking about the Solo 681 P/C kit on the 665. If my plan is simply a swap, no porting, do you guys think I need to worry about measuring squish?

I know it is not an enormous undertaking, but it would require me to buy a few things, calipers, solder, etc. I'm just wondering if I really need to bother. It seems that slapping the gasket that came with the kit on, bolting the sucker up, and running it would be fine.

Thoughts? As a novice, I am thinking that the only reason I would be concerned with squish is if I was contemplating a gasket-less install, in an attempt to squeeze the most power from the saw.

What am I missing?
 

jmssaws

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Squish is super easy to check and I wouldn't get hung up trying to achieve the perfect number. Don't go extremely tight and it will be fine.
 

wildroamer

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I have seen, read, etc enough to feel fairly confident in that. Just don't want to add more work and expense if it's not going to change my install at all.

Top end came with the one gasket...
 

wildroamer

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Thanks, I was rooting for an answer like yours! :biggrin:
 

Marshy

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Because you asked it tells me you really want to dick with it some. My suggestion is to go to Harbor Freight and buy a $10 pair of dial calipers and some solder and check the squish with no gasket installed. Just lightly snug the cylinder bolts and see what the clearance is. If its 0.020 or more without a gasket then go to your local auto parts store and get the proper sealant to do a base gasket delete. The only suggestion I have for you with the solder is get some thin stuff, you dont want to get the really thick stuff. Also, make sure you check the areas of the piston at the wrist pin to minimize piston rock. You can bend a length of solder and stick it in through the spark plug hole. Your welcome, let us know what you end up with. ;)
 

skidooguy

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Last time I had an issue with squish I think i had too much liquor in me and decided that a bigger gal was kinda cute.... I'll let your imagination and/or similar experiences tell the rest.
 
B

Backyard Lumberjack

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successful engine building and modifying is based, in part... on knowledge. data produces information and information produces facts and therein like the knowledge. and one way to get that knowledge is thru measuring things. personally, just me, that is... I cannot fathom a modification such as I assume u r suggesting some kind of BB kit with out measuring tools. ie, micrometer. as stated HF has a very nice $9/10 unit. I have one. really like the accuracy and the numerical read out. you probably don't need to worry about squish, but for many, the deeper you understand ur engine and it parts the better one can take care of it... generally speaking. I measure squish see how it mite change if this or that... I use children's play clay. soft or softer, I prefer not to use solder. if I am off .oo1 or .002 it don't matter to me. I am shooting for 6 hp, not 6,000! lol yes, by all means... tell us what u do, and of course pix always fun to see. good luck with ur project.

to measure squish: small bits clay 4 corners of piston, roll it thru its cycle, remove cyl and measure with your new $10.00 HF digital micrometer... squish expected also tells u if parts manufactured are on course... what if cyl manufactured wrong specs... and squish actually .050... and BB kit runs, but bit sluggish... where do u start to look for answers?... you prob would think its carb H setting... or carb itself...

low buc micrometer, HF:

mic.jpg
 
B

Backyard Lumberjack

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>It seems that slapping the gasket that came with the kit on, bolting the sucker up, and running it would be fine.

you are joking, right! ? :eek: rarely, if ever in my exp... has such an approach as the first two yielded the results stated in #3!

just sayin'...
 

wildroamer

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Thanks for that! I will be looking for a micrometer before attacking this project, and will snap some pics, too.
No H Freight around me, but might just order one. No big hurry anyway.
 

wildroamer

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Well, I wasn't fully joking. I figured that since the 681 and the 665 are the same saw with the exception of the top and, that I could get away with a simple swap. However, ic that I would be better served, on a few fronts, by digging in there and measuring squish, learning a bit more about this stuff, etc.
 
B

Backyard Lumberjack

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Well, I wasn't fully joking. I figured that since the 681 and the 665 are the same saw with the exception of the top and, that I could get away with a simple swap. However, ic that I would be better served, on a few fronts, by digging in there and measuring squish, learning a bit more about this stuff, etc.

hi -

yes, if u ask me, now you are thinking more so like an engine builder... these saws are imo quite complex, have a lot of parts crammed into one small space... there is a lot to putting a new piston pin, circlips, rings, cyl and piston onto a crankcase to ensure proper operation and reliability. good question, though, imo. there is a lot of good informative vids on utube about taking saws apart, repairing with new P & C, rings etc... it is an art just to get the rings on properly and not bend them, or worse break them. I have spent many hours watching some of the better vids, like donnyboy's, just to know and become familiar with the process, etc. it mite 'slap up an bolt together'... but then it has to be tuned and broken in correctly, too. you don't want to burn up what you just created! happens all the time... also a factory Repair/Service manual can be very helpful... too.

BL
 

smokey7

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If it was me I would measure and record everything I can. Including piston to cyl clearance ring gap in multiple places, squish, compression on assembly, pressure vac test info, after first run compression, after break in comp. But....I am a little on the nutty side when it comes to my saws and my records.
 

drf256

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I have a Mititoyu (?spelling) and it's really accurate and fast. Wasn't cheap, but you get what you pay for.

I would always check squish. You don't need to do the 4 quadrant way either. A piece of solder through the plug hole is all u need.

It's cheap insurance. IDK, I do it on every saw. Stock or otherwise.
 

drf256

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Measure the squish. You're mixing and matching parts from two different saws. Manufacturing variations do exist.
100% true.

I just did Backtroller's 034 to ported 036 conversion, and my MS360 building case had a .005 variation in squish from Pat's saw. .015 vs. .020 on my case.

Attention to detail separates the men from the boys in this rodeo.
 
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