Cool head domes... diameter?

[Bancheez]

OK fellas, I am a polaris technician w/ 8 years of experience in the bis (15 yrs w/a wrench in hand) and considered myself a pretty savy mechanic... Recently I decided to get serious about my passion, building high horsepower performance engines. I realized very quickly that I only know a 1/4 of what I "thought" i knew... i would love to get in to just some of the things i have learned in the past 4 days, but as i get further into this, i feel my brain shutting down (overloaded), so i'll get to the stupid question that spawned this thread. I am looking for a couple of you cool head owners to measure the diameter (cross section) of the combustion chamber. see, i have a couple sets of domes here and they both measure slightly different. the standard set is 66mm, the other set is for a 4mm stroke and measure 66.7mm. What is the absolute largest overbore on a stock sleeve banshee? I thought it was 66.5mm. Just curious if there are any other variation in size on these things... If none of this makes sense, please bear with me, im a little shot tonight. i'm done, thanx.

[Bansh-eman]

there are generally 2 differant size domes, small bore and big bore. depending on what size motor your running the dome size will deffer.

 

the absolute last leg of the stock jug is 100 over which puts it at 66.5

 

how ever it is running on very little wall at that point. i want to say that the smallbore domes are 66mm across but I'm not 100% if thats correct. Your best bet would be to send dlnoss a pm on here, he could tell you every thing you could possibly need to know being head makes coolheads and domes for a living

[BellicoseBanshee]

Your best bet would be to send dlnoss a pm on here, he could tell you every thing you could possibly need to know being head makes coolheads and domes for a living.

That is what I would do... :thumbsup:

[Bancheez]

OK, with a slightly clearer head this morning, i think i can explain myself a little better. I just got my set of stock bore cylinders back from Jeff @ F.A.S.T. (4mil port) and started assembling my engine. first, my base gaskets are about .010 thicker than what Jeff recomends. My gaskets are .030 vesrah's, Jeff recomends .020 gaskets (i assembled it anyway so i could check my squish). Then, i installed my Trinity head and checked my squish... .036 - .037, a little tight, but not too much, VERY runnable. So, if i had run the thinner .020 base gaskets, my squish would be .026-.027, OK for a full race engine that gets LOTS of maintenance, but too tight for a reliable trail motor (although, i ran it all last season with .025 squish with no problems... until it pushed an o-ring... then melted a 1/4" hole in my piston) So, satisfied with my squish numbers, i removed the head and sent it w/ my buddy to have it polished. Using the domes out of the trinity head, i was trying to explain, to a good friend of mine, what squish is and how to measure/change it. While holding a 65mm piston up to the dome to illistrate my point, i noticed just how much larger diameter the dome is compared to the piston (1.7mm larger) For a moment, i didn't think these were the correct domes for my set-up. I then realized the largest overbore is 66.5mm, so these domes are more than likely for a stock sleeve banshee. i was just a little overloaded at this point and all i could think was "great, now i have to order a new set of domes b-4 riding" But, after a little Clear thought, i realized everything is going to be OK, but it still doesn't explain why out of 2 sets of domes, the diameter varries from 66mm-66.7mm. I'm not realy asking a question here, just posting up my experience with this set-up. thanx for the responses fellas, and i WILL be contacting dlnoss about dome set-ups. thanx alot

 

 

 

THANX FOR ALL THE HELP JEFF! :thumbsup: