XJ700 Maxim X big bore kit

Is it just me or does this look like it will fit the X as well? I plan to overhaul engine soon and big bore kit is cheaper than OEM separate parts. Plus some extra horses will never hurt lol https://www.cruzinimage.net/2017/08/25/81-84-yamaha-xj750-818cc-bigbore-piston-kits/

 

those pistons will not fit the X.
I increased my 750-X to 911cc by using 87/88 FZR1000 block and pistons.
68 mm bore to 75 mm.
The block required aluminum weld build up and machining where the water pipes attach at the rear.
Also had to machine the block top surface to get the compression ratio back to 11:1 as the 1000 pistons were shorter than the 750.
Keep in mind I did this to the 750-X with a 51.6 mm stroke.
If you have a 700-X the stroke is only 48 mm.
Yamaha used even taller pistons in the 700-X to get the piston all the way to the top of the combustion chamber.
This means you would need to machine even more off the FZR block to get the compression ratio back.
I'm not sure if the cam chain tensioner will take up this much difference.
You would end up with an 848 cc motor.

 

I am wondering why? I mean looking for a project that is supper different? With all the bikes out there to chose from why do a big bore kit overhaul? I understand if it is a show thing but just for a normal bike. To each there own and if you chose to do this please keep a good thread going, would love to see how it works out for you. Big project...wow..good luck.

 

Gotcha. I had my hopes up and my mind racing, but this would too good and too easy to be true. Nothing is easy when it comes to X. It has probably a lot to do with how many of them were made. Not too many options when it comes to altering things. Well, at least OEM's are available.

 

Not a showroom bike but it has little to do with how it would look, rather perform. I just like working on my bike and there are a lot of things that could function better, but don't require immediate attention yet, like gear pinions and gear forks, also piston rings probably, and because this stuff is at the bottom and I'd have to take the engine out than why not do some extra. I don't get excited at all to get all that ish done just so that the bike would function like it did 30+ years ago. I'd rather modify stuff to improve performance, especially if it takes nearly as much time and money. I plan to ride it to another continent, it would be more pricey if something would break down in the middle of ISIS controlled area lol. Now I'm still in the "fishing for information" phase, so I don't know how much I will do to the bike yet. Maybe I will decide to let it all be because I may get into a situation where I'll have to abandon the bike in some third world country. But it would sure be awesome to get it meaner technically. I got very used to how it performs stock riding to other countries annually and pretty much daily in summer.

 

Do you still have this bike? 750X with Fazer 1000 block was on the roads here in Norway, it was totalled a couple years ago. Considering how rare X bikes are I just have to ask lol

 

Yes still have it. more here https://xjbikes.com/forums/threads/highly-modded-650-seca.85760/#post-505494
Back in about 1997 I toured 5,000 kms of Norway, epic ride. Constantly winding along the fjords then a mountain pass to the next fjord.
The pavement just never straightened out.
I rented a 900 Diversion for a week and a few more days on a Ducati ST2
Then I borrowed my brother's 1000 Interceptor the 2nd week, he married a Norwegian girl.

 

When you start mucking with an old engine like these you have to be careful about exceeding the engineering limits on related parts. Just swapping in bigger jugs and pistons can quickly lead to crank balance issues and bearing damage. If you want to make it run better, take it to a builder that knows Yamahas and them do it right.

 

My 911 has been running reliably for 20+ years. It is a proven mod on FZ750's. There is merit to what you stated though. My bike is mostly for show and sunny afternoons riding people around in the sidecar. I would never consider touring far or pushing the performance for extended periods.
Our Norwegian friend (OP) sounds quite adventurous with his bike so I would agree Ryengoth best to keep it as reliable as Yamaha meant it to be.
I'm currently restoring a Turbo and once it is up and running I also plan to muck around with bigger jugs and pistons. I just can't help myself, LOL.

 

Bigger jugs are always more fun...
ANYway, as long as the crank is re-balanced for the additional weight it should be OK. It does not take much harmonic distortion in a high rev situation to wear the bearings into oblivion in short time. If you do take the crank out get the journals WPC treated for less bearing wear.

 

If one needs more power that much a different cycle might be best. For show I get it, but for everyday riding and putting a smile on your face, not sure I would put all that work into it. IMHO If you do that project love to see the write up. Good luck either way.

 

Awesome man, thats good to know!!