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Combustion chamber stuffing

Canadian farm boy

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ok guys got maybe a stupid question for everyone to discuss. I read in another thread(don't remember which) that somebody had put a bolt through into a combustion chamber to try and increase compression and it got me a thinking,

What I'm thinking is that if for example we took an ms260 jug, removed the decomp and then put something like a 1/4" or 5/16" carriage bolt through the decomp hole so the head of the carriage bolt was inside the combustion chamber. This would effectively increase compression which is good but it also changes the shape of the CC which could be bad.
Personally I've never done this but it does have me wondering if this would be worth trying.

What do you guys think?
 

drf256

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I could see it affecting flame travel.

One, large diameter bolt that could be adjusted would be quite interesting on the chainsaw Dyno.

Imagine being able to keep increasing compression to see where power falls off?
 

drf256

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It's tough to get a Tig torch in a chamber. Mike Lee says he's flooded the entire chamber with argon and used a huge stick out to weld a combustion chamber.

I plan on trying it on an 026, but more compression doesn't negate the fact that the model has a 95-98* exhaust at best.
 

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Another thought here, what if a hole was drilled into the very top/center of the CC and then install the carriage bolt? The bolt could be removed and weld added/removed to optimize the shape and adjust compression
 

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Great idea. The only issue I see is the cooling fins.

Could tighten exterior nut, weld onto bolt and grind, so it never loosens.
I thought maybe use a shoulder nut and a brass washer along with some blue loctite. This way the bolt is still removable when making adjustments
 

Motorhead

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Another thought here, what if a hole was drilled into the very top/center of the CC and then install the carriage bolt? The bolt could be removed and weld added/removed to optimize the shape and adjust compression
That would probably work,It would be quite a conversation piece.
 

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If you had to remove a bit off the cooling fins I think it would be ok. There's lots of saws out there that have several missing fins. I think the bolt would also act like a bit of a heat sink helping to pull heat out of the CC
 

drf256

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I could drill that *frencher right on my lathe. Easily put an end mill on the Chuck and make the recess for the bolt.

Cylinder sealing will be an issue.

If a decomp can leak, there's no way we are sealing a carriage bolt through the head.
 

drf256

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Gotta try this on a clamshell motor.
100%

The issue with the comp bump is multi factorial.

It's usually a byproduct of wanting to drop the jug so that one has more leeway with the timing numbers.

The comp bump is usually a side effect of this. The occurrence is generally welcomed, but I've opened chambers at times to reduce compression.
 

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I had wondered about sealing it up too. I figured that something like a brass washer under the nut should work. The brass washer works pretty good for bango bolts and flex lines. Brass also tends to swell a bit when heated so in my mind it should seal up even better as the saw heats up
 

jmssaws

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If you had to remove a bit off the cooling fins I think it would be ok. There's lots of saws out there that have several missing fins. I think the bolt would also act like a bit of a heat sink helping to pull heat out of the CC
I did a 660 over a year ago that had bn squished by a skidder and had almost all of the fins broke off, he wanted to run it so I ported it and he is still running it everyday so I wouldn't worry about a fin or two.
 
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Cut4fun

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Thread the chamber dead in the center. Lock nut on top. Shaped the bolt head as you wish to blend into the chamber like a poor man's torroidal chamber.

I remember a guy trying this in the racesaws build offs back in the day.
 

jacob j.

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The guy that tried it at Racesaws didn't think it out too well and the idea flopped. Sealing is an issue, especially sealing the thing for the long term.

This would be a fairly practical idea for a clamshell saw, but in a professional grade work saw- I'd want to go the traditional route.
 
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