What's up with my cylinder?

muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc
Edited Date/Time 7/28/2021 7:29pm
1984 CR250 Finished assembling engine after 35 years in a box. I've run the engine for about 30 minutes total while trying to sort out the jetting. Pulled the pipe to try and seal up exhaust manifold to pipe with high temp silicone and when I looked inside at the cylinder walls, saw these wear patterns. Pulled the cylinder to get a better look and some pictures. Any ideas what's causing this? Should I bee worried?
The 2 areas above the exhaust port are polished so much that I can barely see the crosshatch.






|
charlie68
Profile picture for user charlie68
Posts
154
Joined
6/28/2019
Location
North Windham, CT US
charlie68 6/21/2021 11:02am
6/21/2021 11:02am
Wow, was the ring end gap in spec?
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/21/2021 11:17am
6/21/2021 11:17am
charlie68 wrote:
Wow, was the ring end gap in spec?
Wiseco instructions are .011" top and .013" bottom
I did .012" and .014"
kb228
Profile picture for user kb228
Posts
6160
Joined
1/31/2018
Location
Mansfield, OH US
kb228 6/21/2021 1:30pm
6/21/2021 1:30pm
Looks like the piston was the wrong size
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/21/2021 2:55pm
6/21/2021 2:55pm
kb228 wrote:
Looks like the piston was the wrong size
I don’t have a bore gauge. But I can fit a .003” feeler gauge between the piston and cylinder wall a .004” won’t fit.

The Shop

See All »
kb228
Profile picture for user kb228
Posts
6160
Joined
1/31/2018
Location
Mansfield, OH US
kb228 6/23/2021 6:12am
6/23/2021 6:12am
kb228 wrote:
Looks like the piston was the wrong size
muc wrote:
I don’t have a bore gauge. But I can fit a .003” feeler gauge between the piston and cylinder wall a .004” won’t fit.
Need a bore gauge.
1
charlie68
Profile picture for user charlie68
Posts
154
Joined
6/28/2019
Location
North Windham, CT US
charlie68 6/23/2021 8:50am
6/23/2021 8:50am
kb228 wrote:
Need a bore gauge.
I agree, the cylinder bore does not appear round.
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/23/2021 10:01am
6/23/2021 10:01am
Before I assembled this engine I took the cylinder, piston and crank to Bill Bune in Anoka MN, talked to Josh. Asked him to check crank and piston to bore fit. He took the parts in back for a few minutes. Told me he couldn’t be sure about the crank because he had another crank in the fixture and because it’s a tin can crank he wouldn’t be able to do anything but he was pretty sure it was fine. Said piston and cylinder were good but rings seemed a little tight and one was upside down. Didn’t want to charge me. Called Wiseco and they told me these are barrel shaped rings and there is no upside down, Said to file another.001” off the rings if I was worried.
Not sure if I should go back there or try to find someone else.
Do I need to go to a motorcycle shop or will any good engine machine shop be able to check this? I don’t want to spend $300-400 for a good bore gauge and I worry that the $50 ones on Amazon won’t be much better than the snap gauges I already have.
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/23/2021 10:03am
6/23/2021 10:03am
Can anyone recommend a good shop in central Minnesota?
TrailDigger 6/23/2021 5:28pm
6/23/2021 5:28pm
Can’t help with a recommendation, but you should be able to find a machine shop with one and ask if they would mind checking the cylinder with you.

Ask what their favorite beer is and bring a 30 rack.
kb228
Profile picture for user kb228
Posts
6160
Joined
1/31/2018
Location
Mansfield, OH US
kb228 6/24/2021 5:58am
6/24/2021 5:58am
muc wrote:
Before I assembled this engine I took the cylinder, piston and crank to Bill Bune in Anoka MN, talked to Josh. Asked him to check crank...
Before I assembled this engine I took the cylinder, piston and crank to Bill Bune in Anoka MN, talked to Josh. Asked him to check crank and piston to bore fit. He took the parts in back for a few minutes. Told me he couldn’t be sure about the crank because he had another crank in the fixture and because it’s a tin can crank he wouldn’t be able to do anything but he was pretty sure it was fine. Said piston and cylinder were good but rings seemed a little tight and one was upside down. Didn’t want to charge me. Called Wiseco and they told me these are barrel shaped rings and there is no upside down, Said to file another.001” off the rings if I was worried.
Not sure if I should go back there or try to find someone else.
Do I need to go to a motorcycle shop or will any good engine machine shop be able to check this? I don’t want to spend $300-400 for a good bore gauge and I worry that the $50 ones on Amazon won’t be much better than the snap gauges I already have.
You dont need a mitutoyo bore gauge. Harbor freight digital calipers give the same measurement as a starrett. Youre paying for quality and longevity. Its not needed for the occasional DIY project.
1
DynoDan22
Profile picture for user DynoDan22
Posts
777
Joined
9/7/2011
Location
Victorville, CA US
DynoDan22 6/24/2021 7:52pm
6/24/2021 7:52pm
Not to be that guy, but you do need a bore gauge to measure a cylinder correctly. I'm also curious about the grooves in the piston.
1
Falcon
Profile picture for user Falcon
Posts
10774
Joined
11/16/2011
Location
Menifee, CA US
Fantasy
407th
Falcon 6/25/2021 9:29am
6/25/2021 9:29am
x4 on the wrong size piston or oval bore. That's an iron sleeve in there, right? I'm trying to remember when Nikasil became a thing... I want to say '85 or '86.
It should be pretty easy for a reputable shop to bore/hone that cylinder to spec. You can go 1x, 2x, or 3x overbore without too much trouble. Then you can go all old-school and say your bike is "boreded-out." Cool Smile

I, too, have never seen a grooved piston like that.
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/25/2021 11:08am
6/25/2021 11:08am
muc wrote:
Before I assembled this engine I took the cylinder, piston and crank to Bill Bune in Anoka MN, talked to Josh. Asked him to check crank...
Before I assembled this engine I took the cylinder, piston and crank to Bill Bune in Anoka MN, talked to Josh. Asked him to check crank and piston to bore fit. He took the parts in back for a few minutes. Told me he couldn’t be sure about the crank because he had another crank in the fixture and because it’s a tin can crank he wouldn’t be able to do anything but he was pretty sure it was fine. Said piston and cylinder were good but rings seemed a little tight and one was upside down. Didn’t want to charge me. Called Wiseco and they told me these are barrel shaped rings and there is no upside down, Said to file another.001” off the rings if I was worried.
Not sure if I should go back there or try to find someone else.
Do I need to go to a motorcycle shop or will any good engine machine shop be able to check this? I don’t want to spend $300-400 for a good bore gauge and I worry that the $50 ones on Amazon won’t be much better than the snap gauges I already have.
kb228 wrote:
You dont need a mitutoyo bore gauge. Harbor freight digital calipers give the same measurement as a starrett. Youre paying for quality and longevity. Its not...
You dont need a mitutoyo bore gauge. Harbor freight digital calipers give the same measurement as a starrett. Youre paying for quality and longevity. Its not needed for the occasional DIY project.
Your experience is different than mine. During the reassembly of this engine I got tired of converting from inches to millimeters so I bought mid level digital caliper when I tested it with my standards from my micrometers, I find it to be off between.0005” to .002” and these deviations are not consistent. But when I test my old starrett dial caliper it is never off more than.001” and is repeatable. Maybe I just got a bad one or maybe those long dead guys who trained me were right when they said “never skimp on precision measuring tools”. I was hoping that all the manufacturing advances made in the last 30 years would result in better cheap tools. But cheap is still cheap and you don’t get what you didn’t pay for.
The cheap bore gauges only touch 2 places in the cylinder. They look like little more than a fancy snap gauge.
muc
Profile picture for user muc
Posts
16
Joined
1/19/2021
Location
Sartell, MN US
muc 6/25/2021 12:11pm
6/25/2021 12:11pm
Yes this is a iron sleeve. It had already been bored .25mm over when I got it. I’m guessing the shop that bored it back in 1985 took it to the.75mm over it’s at now was because that’s the piston they had in stock. Remember that this is an engine that ate cast pistons due to the large exhaust port. If I remember right, the cylinder and piston were in pretty good shape and I only had it bored to try and make it the rest of the season. I had the engine apart for a problem that required me to split the cases.
I used to rebuild outboard motors back in the 70s and early 80s and occasionally I would be given racing pistons with grooves similar to these to install. I assumed these grooves are kind of like how we used to knurl piston skirts to reduce drag back then.
When I called Wiseco about the blue coating on the piston. They told me they had no idea, they didn’t coat pistons back then. But they did warn me about the spirolox wrist pin keepers. Said “don’t lose or deform them because we don’t sell them anymore and wire locks won’t work because of how the piston is cut”.
I’m thinking the cylinder is slightly out of round. I’ve spent some time with my snap gauge and mic. And while I’ve never had the talent to trust myself with a snap gauge, it does seem to be slightly oval. I’m going to try running it like this because if it is too far out of round, I’m going to need a rebore and new piston anyway. Guessing I got nothing to lose?
Thanks for everyone’s help.
SilverSpurs
Profile picture for user SilverSpurs
Posts
561
Joined
2/5/2021
Location
Sarasota, FL US
SilverSpurs 7/26/2021 11:15pm
7/26/2021 11:15pm
You can use a new piston ring to see if the bore is round and or tapered. Look for light between the ring and bore and the change in end gaps. Only good above the exhaust port.

Post a reply to: What's up with my cylinder?