Piston Oil Holes

550 Engine top end rebuild. Figured I'd go large since no OS stuff available at decent price (and I am genetically mean). So why not put a 600 Seca-2 piston into a bored out 550 cylinder - 57 =>58.5mm. But Seca-2 pistons don't appear to have the two holes front and back just beneath the oil ring. Problem ?

 

Could be. The question is (and I do not have the answer for you) if the Seca 2 con-rods have oil jets in the big ends. If they do then you'll want to use those con-rods so the underside of the piston and the wrist pin are adequately cooled. Alternatively you can have oil jets bored into the Seca 2 pistons.

 

Yikes.. Not sure I wanted to go that deep in.. Oil jets on the big ends -is that common ?

 

OK brief research on ebay photos reveals that Seca 2/Diversion con-rods do indeed feature (a single) up facing oil-way/jet. BUT taking a closer look at the 550 that does too. So..

 

I was not aware the the 550 has oil jets in the con rods (I guess someday I'll just have to buy a 550). So it may be that Yamaha determined the piston oil jets were not needed. The 550 engine was made during a transitional period, so one can surmise that the piston oil jets were carryover for the sake of insurance against warranty claims. I don't recall there ever being problems with the Seca II engine in that regard.

This thread may be helpful (or not). http://xjbikes.com/forums/threads/who-made-a-60mm-big-bore-kit-for-the-xj550.39487/

 

Thanks K. Interestingly the xj600/fj600 pistons I already have DO have the holes so it''s only Seca 2 without ?? I wasn't going to use them as I thought they might be too badly scored however on closer inspection it's only on the skirt (not above teh rings) and they might clean up Ok with some scotchbrite

 

Hmmm.... more things that I don't have a definitive answer for. I've never had either a FJ600, or a Seca II apart.

 

Hi , Any opinion on the skirt scoring above ? Usable ?
Cheers..

 

Its simple to just drill the holes in the pistons. I have modified many many pistons- skirt shape/size, oil holes, etc. Not rocket science Just put the holes in as close to the same place, at as close to the same size and run it.

 

I wouldn't unless I had no other option.

 

I've seen worse put back into service, but on cooking car engines, producing half the HP per litre and consequently, more lightly stressed parts.
It's a measurement and judgement call - mic up the skirt and see how worn it actually is.
I think I'd use them on an old snotter that I didn't care about, and be prepared to put up with a bit of cold piston slap for a couple of years until it hits the graveyard. Slappy engines can go on for a long time if they're not thrashed.

 

They measure Ok. I have a feeling this scoring is from when I pulls the block which was rusted/pitted. It's only that bad on two faces out of eight and you can still make out the machining marks on them. Since the scoring is only really on the skirt (not above the rings i figured it might be Ok. I can't justify spending the value of the bike on 4 new piston/ring (approx 400 quid 600 USD !). Also this is going to be a lightly used machine i would think.


PS - All my bikes are 'snotters' - at least I like to think so

 

Give it a go, then. I'd probably re-use an old head gasket to start with, just to fire it up and check it out for a couple of weeks. When and if that blows, fit a new one if no piston trouble has shown itself.

 

Now you're talking my language..

 

I think those pistons are totally fine to run. I have re-used much uglier parts in single cylinder/two stroke applications where piston skirt condition is much more crucial. Make it run and go have fun!