Too Much Ring End Gap? 1985 FJ600

So I decided to put my 1985 FJ600 back together again this winter. The motor had 11,000 miles on it but it was never maintained by the previous owner. Low Compression from worn rings and burned valves. Using a telescoping gage I found the cylinders to be just under the maximum diameter (I am talking .001" under) to be in-spec for a standard size bore. So I honed it with a Flex Hone and fit a new set of standard size rings. When I measured the end gap of the rings a couple of the cylinders were about .001" outside of the maximum spec (spec is .006" to .012").

So my question is, will .001" over negatively effect the compression? I am too far into the motor in terms of time and money to try to find oversize pistons, rings, and a bore job.

Thanks
Tom

 

It won't last.

In hindsight, when you discovered that you were within .001" of maximum diameter you needed to be thinking rebore.

Did you measure the bore in three places, 'mic' the pistons, and compare the piston-to-cylinder dimensions with the spec for piston gap? If that's out of spec too, you might as well stop; you'd be building a grenade.

 

Ditto to what Bigfitz52 said......

 

I will add that using telescoping gages are very suspect to begin with, You just cant take one measurment.. You need to take lots of them and then average them out. Also are your mics correct? all it takes is one light ding and they will not measure correctly.. Your best bet with it being close to tolerance is to take the cylinder to your favorite machine shop and pay them a few bucks to measure the cylinders and have them measure the piston... This is one area where a rookie on mics can miss measure something by a half of a thou and .. Its best to have someone with a set of calibrated inside mics check it for you if you are in doubt.

 

I agree with you guys, but here is some detail:

Std Bore = 2.303" Wear limit = 2.307" Taper limit = .002"

Avg Diam Taper
Bore1 2.3045 .0015
Bore2 2.3055 .0002
Bore3 2.3055 .0001
Bore4 2.3058 .0005

Std Piston Diameter = 2.303" Miked Diameter (.276" from skirt) = 2.303"

Spec for Bore Diam minus Piston Diam = .001" to .002"

I took three measurements at the top, middle and bottom plus3 more at 90 degrees to them. I have a set of Mitutoya micrometer and telescoping gages quality and skill level is top notch.

So Like I said before, I agree with you guys, in a perfect world I would bore and refit with 2nd oversize rings and pistons, but they are no longer available anywhere. I bought two NOS over sized pistons on Ebay a few years ago, but I never saw anymore. I never saw over size rings on-line.

If you guys have a source, please let me know.

So I guess I am stuck, gonna ride a grenade

Thanks for the help!
Tom

 

Very good advice.

That being said, being that close to "out" isn't going to produce the most reliable motor in the world even if it's in spec by a RCH.

If you're building the bike to ride for the next five years or more, then you need to re-think.

If it's just going to be a "Sunday ride" and you won't be hammering it or planning any road trips, then IF it does end up ever so slightly in spec go ahead and put it back together. But set it up a tad rich and stay off the redline.

 

CRAP! I was still typing...

 

It's SOOO close. Be sure you do everything 110% right upon reassembly; and don't "lug" or scream the motor and it might actually not blow up.

First oversize would probably have done it; have you checked the aftermarket; folks like Wiseco? The 600 is a popular retrofit for racing a 550, they might actually offer something. Racing is the only thing that drives the aftermarket on motors this old; look at the MYRIAD of stuff available for the Yammie 500 single because of it.

 

Thanks, I looked at Wisecos web site and I didn't see anything for an fj or a yx600. I may call their tech line and see if they have something that would work. Scream the motor? Redline? No Iam too old for that.
TR

 

Gimme a break. I'm probably older than you are, and my 550 regularly sees redline in at least the first four gears, sometimes five (or even six.) Old is no excuse; old guys can go fast, too.

"Old" is a frame of mind that I refuse to accept; plus all the grey hair helps when you do get pulled over. (I live out in the stix and tend to cruise at 80.)

 

Thanks, I looked at Wisecos web site and I didn't see anything for an fj or a yx600. I may call their tech line and see if they have something that would work. Scream the motor? Redline? No Iam too old for that.
TR

 

Di you have any luck finding oversize pistons? I am looking for some too.