Boring Question...

[brentde3]

I've been doing some extensive work on my r90, and I finally got some numbers back on my bores. Both bores are nearly two one-thousandths out of spec. In addition, both pistons' ring grooves are one one-thousandths out of spec (the rings wobble and, as my awesome mechanic/machinist said, "skip along").

I now seek your wise council on what to do next. He says I can likely hone the bores and install some new rings and keep on trucking for another year or two. Or, I can have them bored and get new pistons (more expensive to be sure).

I can get the pistons from Motobins for ~$480. By the time I pay him for boring and whatnot, I'll be out ~$600. I've got my heads with Ted Porter now, so I'd wind up with an entirely new top end if I went that route.

What would you guys do? Money isn't tight right now, but it isn't terribly loose, either. Things tend to snowball with this bike, and I wind up treating the project like dominoes. I'm all ready in there, so I might as well, so I might as well do that too...so I might as well... You guys know how it goes .

[MANICMECHANIC]

It's already apart, why do it twice?

[88bmwjeff]

It's already apart, why do it twice?

+1

If you can afford it, you might as well get it done right this time, then you can start worrying about the next thing. I mean enjoy riding the bike.

[James.A]

On a well maintained motor, it is nearly impossible to beat out the bottom end. Do this right, right now and you will not live long enough to have to do it again.

[brentde3]

Anything else you'd guys do while you're in this deep? I'll have new bores, pistons, rings, seals, gaskets, heads, etc. Should I look at the lifters or connecting rods, or, or, or? All in the spirit of doing it right, of course.

[MANICMECHANIC]

How is the clutch? I presume you've got a new rear main seal and oil pump O-ring. How about the timing set?

[brentde3]

New main oil seal, yes. Clutch has been fine. Timing's been fine. Splines were done the winter I bought her (two-ish years ago).

[88bmwjeff]

Anything else you'd guys do while you're in this deep? I'll have new bores, pistons, rings, seals, gaskets, heads, etc. Should I look at the lifters or connecting rods, or, or, or? All in the spirit of doing it right, of course.

Well, you didn't say how many miles are on the engine, but I'm guessing it's not a low mileage engine given the specs of the bores. That being said, I'm not much of an expert here. But, I would at least pull and check the tappets/cam followers. For peace of mind, you could pull the con rods and check the bearings and while they're off you can have them balanced with the pistons. Having things balanced will lead to a much smoother engine. Of course it's all time and money, and you need to determine how much time and money you want to put into it.

[lkchris]

Fitting new Nikasil pistons/cylinders will make for a much more reliable bike. Compare the cost at least.

[krpreston]

Fitting new Nikasil pistons/cylinders will make for a much more reliable bike. Compare the cost at least.

I was about to say the same thing when you beat me to it!

[85K100LT]

"I can get the pistons from Motobins for ~$480"


I would shop around on those piston $240 for a single piston sounds high.

Do some more research - got to be a better price out there!!!!

Let us know what you find.

[brentde3]

Hucky's first oversize R90 piston is $370 for one.

Max wants the same. Any other ideas for sources?

[85K100LT]

WOW - I looked could not find any - Cost is crazy!!


No ideas!!


or call

www.motoghost.com

he might have a source.

"I've been doing some extensive work on my r90, and I finally got some numbers back on my bores. Both bores are nearly two one-thousandths out of spec. In addition, both pistons' ring grooves are one one-thousandths out of spec (the rings wobble and, as my awesome mechanic/machinist said, "skip along")."


If you put it together with these specs it will run fine for the next 100,000 miles - the beauty of Airheads!!!!


or:

http://cgi.ebay.com/ebaymotors/Pisto...Q5fAccessories

[ISAMEMON]

the e-bay pistons are sold already, was that you ?
the nikasil is the way I would go.
and if your gonna go bigger why not chase down r100 ?
my previous bmw was not a nik bike and at 110k it was just out of specs, and I know I could have just slapped new rings in and been good for many a mile, as it was not burning oil as it was, but I instead found a cheap set of low miles jugs and pistons wihtin specs and went that route.
my current bike is a nikasil bike, at 90k it needed a few things, including of course push rod tube seals,
pulled it all apart and bores were within specs so just went with new rings so the nikasil deffinetly hold up, and this was nolt a nicely treated bike by p.o.

while I was "in it" it was not a bunch more to put in new con rod bearings ( preventative and cheap) and got the pistons , rods balanced. I dont remeber the specs, but I was surprised how far out "balance" they were for being a bmw.
I also pulled the lifters, and one was galling, you dont want to see pits, so I replaced two of the 4 and had them balanced as well, for the heck of it while everything else was beeing balanced, no added cost, why not, benefits ?????

I also toook the approach, well its apart fix it now, and did tons more then originally intended, but Ill be good for another 100k plus ( for the lower end anyway)

good luck with yours

[44006]

"He says I can likely hone the bores and install some new rings and keep on trucking for another year or two"

I would go this route and keep my eyes open for another bike or engine with better parts.
Probably if you weren't down and itching to ride you would have the patience or luck to
find what you need long before you really need it. A lot of other crap can happen in two
years to change your life forever. For what it is worth from my point of view why spend
a small fortune and miss riding time with all that perfectionist crap. If it works just ride it
till it doesn't work.