Author Topic: Dolmar 7900 Porting Info  (Read 3795 times)

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Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #30 on: January 08, 2012, 10:38:32 am »
The quote thingy ain't working for me...... :-[

Ed the ratio your speaking of, is this crankcase to displacement?

Read the 2 ways to do it since update by server.   http://chainsawrepair.createaforum.com/general-discussion/%27quote%27-not-working/

Cool. :)
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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #31 on: January 08, 2012, 10:26:54 pm »
Sorry I thought someone answered your question and yes its total volume to engine cc ratio

Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #32 on: January 10, 2012, 07:36:44 pm »
I will be building a 7900 worksaw here again in a week or so, it will have the unlimited coil in it thou , not sure why but the owner wants one in it , the saw will be used to block firewood mostly in the 20 to 24 inch diameter in oak and maple

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #33 on: January 10, 2012, 11:28:46 pm »
I will be building a 7900 worksaw here again in a week or so, it will have the unlimited coil in it thou , not sure why but the owner wants one in it , the saw will be used to block firewood mostly in the 20 to 24 inch diameter in oak and maple

I have one here to build as well. I need a few days to get caught up before I start on it. The owner says he wants a GTG saw out of it so...........

What would you recommend????

Thanks Ed for the replies.
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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #34 on: January 11, 2012, 07:18:02 am »
if your using the stock piston then becarefull on the port timing , really watch your transfer porting as to high the motor lays down in the cut but if the guy can run the saw and cutting smaller wood then you can get away with the higher transfers , so go after compression

Offline w8ye

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Re: Dolmar 7900 Porting Info
« Reply #35 on: January 11, 2012, 09:45:03 am »
But is the combustion chamber pent roof offset in the 7900?

If so, it would require some fancy offset machining for the pop up?

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #36 on: January 11, 2012, 10:30:04 am »
But is the combustion chamber pent roof offset in the 7900?


If so, it would require some fancy offset machining for the pop up?


The offset popup is not an problem. They are no harder to make than a standard popup.

When you add a D shape to an offset the milling machine comes into play, but it still is just a simple task.

if your using the stock piston then becarefull on the port timing , really watch your transfer porting as to high the motor lays down in the cut but if the guy can run the saw and cutting smaller wood then you can get away with the higher transfers , so go after compression

I'll be tearing it down in the next few days to clean it up real well. If the piston has any wear to speak of I'll try to get a 272 piston.

I just did a 064BB with a 395 piston and it has a butt load of torque but not as much unloaded rpm as I used to seeing on an 1122 series Stihl.

I'll be going back in it another time or two.  ;)
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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #37 on: January 11, 2012, 03:20:18 pm »
just watch how many rpms you end up turning with those 395 pistons cause they break , the ring land cannot stand real high rpms at all and yes that is on OEM

Offline Mastermind

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Re: Dolmar 7900 Porting Info
« Reply #38 on: January 11, 2012, 04:43:03 pm »
The BB Stihl is turning 13,400
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Offline EHP

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Re: Dolmar 7900 Porting Info
« Reply #39 on: January 11, 2012, 07:14:49 pm »
that should be safe , I never had much trouble on gas but lots of trouble on alcohol , On muffler none broke but as soon as you put them on pipe and try turning 13,800 rpms in the wood they seem not to be able to stand that

 

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