Heads

[oldjapanesebikes]

Not sure how, but the first post disappeared so second time lucky (I hope).

I could use a bit of help from the board members - I have been sorting through a number of cylinder heads I have in preparation for an update to the Field Guide for the GT750, and would like some help in getting an idea of which engines they'd go with. If you could please take a moment, and look at the photo below:



From left to right these are an early J, another J/early K and a mid-range K - looking at the left head, note that the front fins are a uniform 'waterfall' shape, plus there is a small extra fin just by the thermostat housing. As a matter of interest to odd people like me, this also matches the image used in the parts manuals and is part number 11111-31001. (there was a 11111-31002 which was the split head variant) The middle head is still of the waterfall design, but the small fin has been dropped from the casting. I have several examples of this and so am sure it is a casting change and hasn't been snapped off. The head on the right is the design used through till end of production and was introduced in the K production (part number 11111-31003) in which the front fins are shaped much differently in front of each of the leading edge main cylinder head bolts. The only difference introduced later was that later heads were planed 0.2 mm starting at engine GT750-57533 to increase the compression ratio. What I'd like to know then is when did the J changes happen ? If you have a J, could you just take a look and if yours matches the left or middle head, please PM me the engine number and which one you have ?

Addition: while you are looking, if you also have the early style full waterfall with additional tab head, are you also missing the additional cross brace between the front down tubes that was added at some point ? This was added across the frame just below the cooling fan and early J's don't have one.

Any help you can offer would be greatly appreciated ! I'll use this information in the updated version of the field guide I'm working on - the current version is available here.
http://oldjapanesebikes.com/fieldguide/ ... cover.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[oldjapanesebikes]

Bump.

[tz375]

Ian,

This won't help much as all bar one of the heads I have here are the later type. The one early head came from a J with a matching set of barrels with the bolt on flanges. I'd speculate that barrels and heads changed together

[oldjapanesebikes]

Thanks Richard - actually that does help as it supports what I'm seeing - the bolt on carb boot change to a spigot mount happened at about frame 21133 - from that frame and higher they seem to have the stepped fins seen on the right of the photo. Prior to that frame they seem to have had one of the earlier style of heads.

And as well, the added bracing cross bar between the front down tubes appears some time after frame 22932, but before frame 31319 so that is also starting to narrow down. And yes, its boring and won't solve world hunger, but it does help to pass the time .....................