Pulling head on YZF750---

Want the specs for a valve adjustment? Can you provide tips for bleeding brakes? Please use this section.
dfrois
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Post by dfrois »

Hi all,

been away a while, I`m surprised this thread still lasts! Anyway, if I understand correctly, the problem at hand is that the 1000 block is too tall for mounting on the 750 crank. It needs 16mm shaved off, which can`t be done without damage. So, here`s a thought:

Standard Yamaha repair procedure involves removing liners and inserting new ones, on a press (Yamaha says they are not rectifiable). So, what about removing the liners, and then shaving 16mm off the bottom of the block, instead of the top? Then, reinsert liners as if new...probably ground 16mm from the bottom as well. I can`t see why it shouldn`t work, and camchain path should not be disturbed too much.

Never done it, though, so I may be talking nonsense. Please correct me if so!

As for CR woes, there is another approach that I have not seen mentioned here yet. A smaller-than-wanted chamber can be profitably turned into a tuning advantage if the chamber is worked around the valves to increase its volume. The idea is to create a bigger-than-standard clearance between valves and combustion chamber walls, so that the flow area at low valve lifts is no longer shrouded by the walls. This is usually done in many heads, and the limit is (you guessed it...) that removing too much metal will drop the compression too much, and skimming the head a great deal to get it back can bring about valve/piston contact, which means making or increasing valve cutouts on piston tops, which then negates the flow increase, etc., etc. But, starting with a smaller head can be an advantage here. Not easy, though; hardest part is making shape the same on all chambers while retaining same volume!
:)
DF

KontoBoy
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Post by KontoBoy »

Well, my motor is back together now--not in the bike yet but it will be soon so this thread is more academic now.

Shaving the bottom off is going to take off all the gasket mating surfaces. See the pics in my previous post. Maybe that's not so bad, but pressing in and out sleeves and since you working from the bottom, shaving the sleeves is also going to drive up costs.

The same goes for machining the combustion chamber. It's beyond my expertise (hell, Im probably already there) and taking it to a shop is $$ I don't have. I was looking for cheap power--probably an illusion. (In the last month I've paid enough in room, board, books, laptops and tuition to buy a nice new R1).

I did ask LA Sleeve about options for resleeving the 750 cylinder (76 inside, 81 out, 6mm top lip). No reply yet.

The 750 forum raised another issue on using the 1040 kit in a 750. Apparently the 1000 and 750 heads are different and the center intake valve will bump the 1040 pistons running in a 1000 cylinder block. Ouch!

Kontoboy

cromwelluk
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YZF 750 top end

Post by cromwelluk »

Kontoboy

It looks like me and you have got the same spares just sitting in the garage.
The “dream of looking for cheap power--probably is an illusion”
Looks like the Yzf 750 was a bit of an odd ball to get cheap & easy power

It seems the best way forwards is FZR 1000 crank. Piston’s, Head & may be Carbs to save re-jetting ?
Giving a 6 speed FZR 1000, but it’s a total engine rebuild and dot a direct fit as it need s either an adaptor plate or the frame drilling for the head mounting bolts

The last option may be using the Pistons form a FZR 1000 exup and see if the sleeves from a FZR 1000 can be machined to fit

Someone must know if it can be done

Crommie

KontoBoy
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Post by KontoBoy »

I still have that YZF1000 head too. Maybe the sleeves can be pushed out and reused.

No reply from LA sleeeve. I need to call. It seems only half the vendors ever answer the tech support questions submitted on-line.

Kontoboy

jjs777
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Post by jjs777 »

exupturbo wrote:The artical was in a UK mag either "Performance Bikes" or "Superbike" if my memory serves correct and it had a picture of the FZR911 and another bike doing a wheely on the front cover, it was a long time ago though so finding one might be a problem unless a UK brother has a copy to scan ? Condition of the barrels is not really a problem as they are going to be bored and skimed anyway. The 750 and 1000 exup have identical crank cases, the only difference is the length of the cylinder head bolts due to the taller barrels and longer stroke on the 1000, there is nothing stopping you building a complete 1000cc motor into your cases but this will involve using a 1000cc cylinder head and some brackets to allow for the increase in height of the cylinder block as the head mounting to frame point will be out of alignment.
If I find any more info I will let you know ;)

Mark
yeah the 911 article is on our server...
http://www.exupbrotherhood1.com/brother ... onversion/

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