Hi, I'm doing a bit of engine research and have a couple of questions regarding the Gen II engine. (1) Does anyone know the cylinder bore pitch? (2) My understanding is that it is the same as the Gen I bore pitch but I may be wrong... i.e. the Gen I has a smaller bore but the pitch is the same. Is this correct?
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wildweasel_pt
Well-Known Member
By pitch you mean the stroke? i.e. the distance between TDC and BDC?
Zeus36
Well-Known Member
Bore pitch is the distance between the centerline of a cylinder bore to the centerline of the next cylinder bore adjacent to it in an internal combustion engine
Gotcha......I can find almost every dimension related to the engine (in the service manual) other than pitch.
Zeus36
Well-Known Member
Someone will have to measure it for you on both generations. I don't find it on the web or in the service manual. No evidence of Yamaha's engine blueprints online either.
Thanks Zeus36, I'll wait and see if someone happens to tear down their engine and can get the measurement and if not I'll end up buying a junk set of engine cases on ebay. I'm prepared to pay to cover the time taken for taking these measurements.
Thanks
Thanks
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wildweasel_pt
Well-Known Member
I'm curious to know why do you need those dimensions
I'm curious as to the interchangeability of parts between the Gen 1 & 2 as I love modifying things. If the bore centers are the same between Gen 1 & 2 then there's every chance you might be able to use a Gen 2 head on a slightly bored out Gen I engine. Not all the way to 90mm like the Gen II but certainly somewhere around 80 to 85mm. It'd need some modification but I'm no stranger to that. The engine being an "open deck" design would be a perfect candidate for Darton "Mid" Sleeves. You might say it'd be cheaper to just buy a Gen II but that wouldn't be as much fun... I just found out that the Gen I cylinder pitch is 146mm.
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wildweasel_pt
Well-Known Member
Cool. I like visionaries and proactive people. Good luck
Ain't never going to happen. Using Gen 2 parts on a gen 1 is simply not practical to do. Everything is on a larger scale. Here's the requested information.
70 mm between side walls plus the bore centers gives you 160mm bore spacing (which is what we always called it - not pitch).
Pictures include the measurement of the wall to wall (obviously not perfect to measure this way but plenty close to give you the idea). Copper gasket is 87mm (vs 90mm of the stock gen 2 bore). Other gasket is stock Vmax 76mm bore. Even shifted to the side the copper 87mm gasket shows just how far out it is from being able to work.
Keep in mind that the largest you can bore the stock gen 1 without head alteration is 83mm. After that it can be used but performance starts to suffer since the piston becomes heavily shrouded.
70 mm between side walls plus the bore centers gives you 160mm bore spacing (which is what we always called it - not pitch).
Pictures include the measurement of the wall to wall (obviously not perfect to measure this way but plenty close to give you the idea). Copper gasket is 87mm (vs 90mm of the stock gen 2 bore). Other gasket is stock Vmax 76mm bore. Even shifted to the side the copper 87mm gasket shows just how far out it is from being able to work.
Keep in mind that the largest you can bore the stock gen 1 without head alteration is 83mm. After that it can be used but performance starts to suffer since the piston becomes heavily shrouded.
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Just to clarify things: (a) I personally have always called it bore spacing or bore centers however google lists 3 times as many hits using "bore pitch" as "bore spacing" and most forums I frequent, use "pitch" so in order to not cause confusion I used "pitch". (b) You are right in that it is never going to happen however please remember my first words which were that I was INVESTIGATING in case the bore pitch/spacing/centers were the same. They are not so yes, it's not going to happen. (c) I was only interested in boring it out IF I could have used the Gen II head. I can't due to different bore spacings so therefore and to use your words again, it ain't going to happen. (d) I am very grateful that you measured this and as a result answered my questions.
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The gen 2 heads in my opinion are not that greater in efficiency anyway. If you look a the power output between the gen 1 vs the gen 2 it's mostly a function of CC's.
1200cc stock generates 115 rwhp = .09583 HP per CC
1200cc with header/jet kit 125 rwhp = .1042 HP per CC
1700cc stock generates 170 rwhp = .1000 HP per CC
1700cc with header/reflash 185 rwhp = .1088 HP per CC
The bulk of the power is created with the increased CC's. I am sure that there are slight increases in power from the head design but a large part of what's left is due to the compression increase.
What's your end goal? I have seen a few sets of billet gen 1 heads which could be made to make more power (usually shifts the power band up as well which hurts low end).
1200cc stock generates 115 rwhp = .09583 HP per CC
1200cc with header/jet kit 125 rwhp = .1042 HP per CC
1700cc stock generates 170 rwhp = .1000 HP per CC
1700cc with header/reflash 185 rwhp = .1088 HP per CC
The bulk of the power is created with the increased CC's. I am sure that there are slight increases in power from the head design but a large part of what's left is due to the compression increase.
What's your end goal? I have seen a few sets of billet gen 1 heads which could be made to make more power (usually shifts the power band up as well which hurts low end).
