Bore sizes

All, just dismantled my 1981 xj550 uk spec engine 4v8 ?? Standard
I had hoped it would be standard bore of 57mm and i would hone/ deglaze the bores fit new rings do a valve refurb and rebuild.
I measure the bore and Piston diameter and find it to be 59 mm.

Is this possible as all imfo i read over here is max bore is 1 mm oversize . I.e 4 times 0.25 mm

I wonder if anyone can help or do i look for second hand cylinder block .

As you are aware this model was not a big seller in uk compared to US/ Canada so parts rare second hand and carraige costs on large parts from N America are prohibitive.

Look forward to any reply that may help.

 

It sounds like a different engine has been installed..............what is the engine code on the block and the cc size on cylinder jugs....see Page 4 and up:

http://www.xj4ever.com/catalog/frame-engine-id.pdf

 

XJ600s and Radians have 58.5mm bores. Could be one of those with a +0.5 or standard bore and inaccurate measurement. 598 on the block is the tell-tale sign of a 600 a 550 is in fact 528. Is your compression down? Before messing too much bear in mind a set of rings x4 will be over 200 quid.

BTW 550s sold well in the UK, 2nd hand parts parts are plentiful on UK ebay and German ebay..

 

Engine number *4V8. 000501*
Number on block 528

Hold fire , i might get different measuring tools as i was using a new digital vernier and an internal bore micrometer( old and no calibration date)
You wouldnt think they would both be wrong but thats where i suppose could get thrown off track.
So will get back when ive done above.
Dont suppose a 528 block could be bored out to accommodate larger pistons etc?.

 

Could be, but if so, someone went to a LOT of effort to do so, since Yamaha only makes pistons in 4 oversizes, the largest being +1.00mm (thus 59.00mm on a 528cc engine). BTW, O/S pistons are normally stamped on the crown with the o/s dimension, i.e. +.25, +.50, +1.00, etc. Cutting a 58.00 bore engine (the 528 engine) to that large of a diameter would mean running really thin cylinder liners......although 598 engines use the same physical size jugs, their liner bores are cast slightly bigger, so that the larger cast-iron liners can maintain their specified thickness (3mm, I think, but don't quote me on that............).

 

Will check piston crowns tomorrow to see if any numbers stamped on them, in mean time thanks for your help both

 

there is an old thread about doing over sized bore for larger pistons to a 550

 

The piston crowns have between the valve recesses the letter C and an arrow facing front of the engine. On the piston at the ignition pick up side there is a very faint line which might be seen as a number 1 but not definite.On next piston a 2 then next a 3. On the piston at the clutch side there is only the arrow and the C . I suppose if these are numbers for the pistons then number 4 is obvious by default.

Any ideas? New to forum is it difficult to upload pictures?

 

you can use a photo host site and post the link, or click upload file or more options for photos

 

I thought the 528 motor used 57mm pistons..

Kickaha (the 550 modification expert on here) I think suggests 2mm as minimum bore liner 'meat' is acceptable.

BTW does your motor have a rev-counter drive coming from the head?

 

Yes rev counter from exhaust side of head.

 

You are correct, my error.

The arrow is correct, as it indicated proper orientation of an installed piston (the arrows should point towards the front of the engine). But pistons are not labeled/cast with a piston location mark (1, 2, 3, or 4) from the factory, it may be that someone was inside that engine previously and marked them for "correct" re-assembly purposes.

 

That was a figure given by my engine builder, I had it bored to use standard 58.5mm XJ600 pistons using the XJ550 cylinder barrel

 

OK so Rev counter means its a 528 head - If they are 59mm pistons you're looking at a 566 cc motor - which I dont think I've heard of. A set of original size 528 barrels should be easy enough to pick up and if they are under 50k miles a new set of rings
will see you good I think. BUT if the 59mm bore is real has the head been machined to match?

 

All, thanks for your help, i have been in France for work purposes so unable to confirm accurately the piston/bore sizes. Will do so shortly when i aquire measuring gear and expertise and also as is best second person to confirm my measurements. Back soon

 

We'll be waiting ;-)

 

Sorry for delay in coming back. To update, I took a100man advice and managed to source a cylinder block complete with pistons which are standard bore (57mm) from internet.

Hopefully this weekend I will hone bores to deglaze\freshen up and source new set of rings and start rebuild. .

Thanks all.

 

Hi Hamish

I would measure your ring end clearance before consigning them to the bin - new ones are expensive and somehow unlike Honda SOHC stuff quite rare - lthough Len stocks them at I think the best price. BTW what about the head? Was it altered to match your unusually large bore? How about any history of the machine. It is intriguing.

 

My motor builder from back in the day, re- sleeved my cylinders and bored the cases to fit for oversize Honda pistons.

 

Dont think head was altered but i suspect head gasket was blowing between cylinders 3 and 4. Cant help much with the history im afraid. I bought as non runner. Got it running but looks rich. Dont have colortune yet. Mota (neta) exhaust fitted. What jets should be in or does it matter with that exhaust?