Too big bore or not to big bore.

[capitanoinsano]

Hello
I am getting my head redone due to a leaking valve seal.  Bike has only 20k miles.  I get a small cloud of smoke if the bike sits for a couple of days, but problem goes away if its warm enough outside that the engine never gets cold.  The cloud of smoke happens about 10 seconds after startup, then clears away, then no smoke whatsoever, and no oil consumption.  Bike runs perfect though especialy since factory pro jet kit and emulsion tubes.

So while the heads off.....  I'm considering the 1219 Wiseco big bore kit.  I am not really after more power.  I use the bike for touring use more than sport use... Well I tell myself that till I get out in the open somewhere.  While the head is off I could have that done by a great local engine builder that I know.  But I'm thinking the forged pistons could be a reliability upgrade but could also be a liability.  The skirts surely would be stronger, no crumbling with forged.  But the stock ones usually last many miles too.  The negative is the extra clearance for the piston which expands more and means more warm up time and possibly more bore wear and ring wear.

Is the lifespan of bores and reliability better with the Wiseco pistons?  Has anyone went 50k on a set in an fj1200?   There is also aluminum sleeves and nikosil, that would eliminate the need for extra clearance, but would add 1000 dollars or more to the project.  Also, is a big bore fj1200 harder to start?

[higbonzo]

I have about 53,000 miles on my bike and it doesn't smoke.  I had it on the dyno and it hit 102 but the clutch went so I didn't get an accurate dyno.  Oh, and that was the original clutch.  I've heard of these motors running untouch for well over 100,000 miles.  I had a 550 Maxim and road it hard all the time, and it didn't start smoking until about 70,000 miles.  Yamaha make strong engines.

Later.....

[capitanoinsano]

The smoke I have is not smoke from wear (rings, valve guides, etc).  It is an old hard valve seal (or two) which are letting oil seep onto the valve when the bike is sitting (especially if its cold out).   When it runs for a few seconds the oozes around the valve as it opens and closes and you get smoke.   Sometimes valve seals do that.  If it were rings it would keep smoking when you ride it, but it makes no smoke after the first 20 seconds.  I understand this is classic valve seat seepage.

I have read of rare cases of skirts failing on the cast pistons, so was considering a big bore kit, but probably won't as I am mostly happy with the power I have now.  Gas mileage is excellent, at least 45 on the highway going near 65 mph.   May go down a bit as I added a factory pro jet kit, but probably not much.

[FJmonkey]

I cannot say much on the big bore but my 86' has 60K+ and it smokes at start up, I figure its over 18 so I cannot legally do anything about it. I don't have to kiss it, just ride it like I stole it. 

[andyb]

Let me see if I'm reading this right.

Bike does everything you want it to do, smokes a little and needs a little headwork done to fix that.

So you want to tear it apart and soup it up?  Why not just fix it and enjoy it as it is, if it's doing everything you want it to do?

You could consider something like retiming the cams to shift the powerband around and perk up the midrange, for a rather smaller expenditure.  The only reason to rebuild a good-running motor that completely is in search of more power.  The question is really if you're after that kind of power or not, and if the FJ is appropriate to put that type of money into.

[higbonzo]

You know you can always go with a about 4-5 teeth bigger back sprocket if you are just after more acceleration.  You are still going to be able to run up to 140 mph, but it will feel like you put a new motor in while you are taking the trip there.   The other reality is, if you have not done any wheel and tire upgrades you are just go to spin your tire further and faster.  You may want to improve your braking, suspension, wheels, before you go throwing a bunch more horsepower at the bike.  Just my $0.02

later.....

[capitanoinsano]

The last thing I want to do is drop gearing.  I like it that it cruises smooth on the freeway at 75-80 without taching 6-7 grand.  The big bore kit would make more power everywhere, but just not sure its worth doing.  Cast pistons can fall apart, doesn't happen often, and usually when poor maintenance on carbs and fuel lines clogs a main jet.  But its pretty hard to break a forged wiseco piston.  My question is does the extra clearance required cause other headaches and shorter lifespan of bores.  While the head is off would be the time to do it, but I'm leaning to staying stock and just bumping cam timing a hair.

[capitanoinsano]

The reason I want to fix it, is that if the valve seals are hard (or some), or cracked, they (or it) could fail completely when I'm 500 miles from home.  I'd make it back home, but it could cause plug fouling, oil loss and smoking all the way home.

While its open I'm replacing all cam chain tensioner parts. They are 20 years old and while its open, might as well.

[Pat Conlon]

Hey Mark, as I understand your basic question is; New aftermarket pistons: Forged or cast? (don't know any that are not forged)
A question to the group: Are the oem FJ pistons forged or are they cast? I've heard that they are forged.

I know that Frank and Steve are very careful about letting their monster 1450cc FJ motors warm up.
Yes, we know that the denser forged pistons expand more than cast (or the superior hypereutectic) pistons, so more piston to wall clearance is needed, and thus the possibility of the dreaded cold slap with forged pistons.
On water cooled engines this could be a problem but watching Frank and Steve I note that our air cooled FJ motors warm up quickly, esp. when standing still.

RE: Warm up; Frank has a theory and I believe he is right: The majority of engine wear occurs when a FJ motor is run hard before the *oil temperature* is correct, which we know happens several minutes after the engine cylinders are warm.

I *think* our FJ motors already have oem forged pistons (any help here?)

IMO It will be hard to notice the power difference in the small bump in displacement to 1219cc  like you would going from 1200 to 1450 monster.

You mentioned Niksil lined cylinder bores: Yes, better heat transfer so they run cooler with tighter clearances. A popular mod is installing the XJR 1250 pistons and cylinders which are oem Niksil plated. These XJR cylinders are the basis for the monster 1450cc motors. Hank and Randy takes the XJR1250 cylinder and bores it out and sleeves them for the large (forged) pistons.

Go ahead and fix your valve seals  (w/Viton seals) and call it a day, or go ahead and do the whole top end while you're at it...

While the head's off, if your cylinder bore measurements are in spec. leave them alone.

Cheers.

[Pat Conlon]

Correction to the above. Frank's and Steve's motors are 1349cc's not 1450cc's....

[capitanoinsano]

I don't think the stock pistons are forged.  They are made by ART (Japanese company) for most japanese bikes.  So they are all a "work of ART"...sorry.

Anyway, that is why Wiseco says their pistons need another .001" of bore clearance to piston.  I don't think there were any air cooled bikes that came with forged pistons, and the majority of watercooled bikes are not forged.   For example, I have a 2000 Triumph Speed Triple 955i.  Stock pistons were cast aluminum with steel sleeve bores (typical).  I put a Triumph Daytona engine in it last winter, now it has an engine with forged pistons with nikosil over aluminum bores.

Steel sleeves and cast pistons are normally used together.  Forged pistons and Nikosil bores are normally used together.  The reason is the thermal expansion coefficients are similar.   When you put a forged piston in a steel sleeve, you don't have as good a match.   But if you let the bike warm up well its ok I think.

[andyb]

Pretty sure OEM are cast.

They sure break easily enough, usually a forging will bend and cast will shatter.

Don't drop either, but I can tell you the skirts will break off the OEM's pretty easily.

[capitanoinsano]

Piston slap may not always cause problems.  My 95 Buick Lesabre with the legendary 3.8 has piston slap for the first 10 seconds after starting.  There were many complaints about piston slap that year even with low miles.  It was due to piston pin tolerance.  But it doesn't seem to hurt anything as the owners claim to have had slap on startup for 200,000 miles but still running.

[capitanoinsano]

I think air cooled engines actually take longer to warm up than water cooled (but I could be wrong).  The reason I think that is because on a water cooled engine you have no cooling fins and with the thermostat shut, not much cooling by heat transfer to air.  Also water cooled engines have less metal in the cylinders and heads (I think).  Also air cooled engines are tuned  so the gas can help cool things down.  I am not sure they really use more gasoline, its just that since the air cooled engine runs a little hotter, the air/fuel ratio is richer than it needs to be for that combustion temperature (a warmer charge or air and fuel needs a little less fuel).

If it takes more time for an air cooled engine to warm up, then with a wiseco kit you will have quite a bit of waiting to do.  But the higher compression of the Wiseco kit (10.25 vs 9.7) will help speed things up.

[capitanoinsano]

Ok, so I contacted Hank Scott Racing.  He recommended a 1201 kit (may have been 1200 or 1202, but around there somewhere) Wiseco kit. He has them made for him by Wiseco. He said the FJ1200's sometimes didn't have the most accurate bores from the factory.  He thinks my brief smoke at startup may not be valve seals, but bore tolerances, but most think it is valve seals.  He also said he runs the Wiseco's with 1.5 thousands clearance and its fine.  I think that is same as stock.  His opinion is that the big bore kit is a reliability upgrade.

So I'm thinking Wiseco, but I'll get the one he recommends, price was competitive too.  To run aluminum sleeves with nikosil you would have to bore out the cases as the sleeves need to be thicker than the steel sleeves from the factory.