Can I get a piston read?

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12/15/2018 6:20 AM

1988 Rm 250 full rebuild about 4 years ago, 8-10 hrs run time, was running good, 1 ring piston, figured I would pull it down to inspect. Cylinder replated & piston matched by Powersealusa. I use Evans waterless coolant, it is clear With a blue tint when new, when I drained it it was darker & had a 2 stroke burned oil smell, like exhaust gases were being pushed into the coolant system...it did not overheat & I did not find coolant in the pipe....the underside looks brand new, no oil stains. The sidewalls of the piston are near perfect. all opinion are encouraged & welcome...thanks... Photo
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12/15/2018 6:22 AM

The head Photo

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12/15/2018 6:29 AM

The cylinder..! It looks like hell, but you cannot feel anything with your finger nail......I have not measured piston to cylinder and ring end gap yet.........The previous owner had the cylinder resleeved, which I"m not a big fan of. Powersealusa said the sleeve looked good and I had them plate the cylinder & match the piston. Photo
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12/15/2018 6:30 AM

Piston looks fine. My guess is you've got a head gasket leak. Looks like it's been compressing water from seeing the dome.

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12/15/2018 6:51 AM

Harry Backmon wrote:

Piston looks fine. My guess is you've got a head gasket leak. Looks like it's been compressing water from seeing the dome.

Thanks for your opinion Harry....I still have to clean off the gasket material for the head & cylinder tops, but a quick check for warpage did show 1 spot on the head that exceeded tolerances as per the Suzuki manual..but just barely...I will surface both for sure....

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12/15/2018 7:51 AM

I see a good bit of blow by on the piston rings. The cylinder shows it is not getting a good seal to the piston ring.
I would have the piston to cylinder fit checked as well as the ring end gap.
I too suspect a leaking head gasket.

Paw Paw

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12/15/2018 8:59 AM

I had an older RM with heads studs start to push water around the studs. I took the studs out and cleaned them up with a wire brush, once removed I could do a better job of cleaning the cylinder for a new head gasket. I would put a small amount of Yamabond on the studs when I reinstalled them to keep them from pushing water again. Only bike I ever saw do this.

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2018 KX450F
2005 KX250
2003 KDX 220
1984 KX 80
1982 RM 80
1980 RM 80
1977 XR 75
1969 Honda Mini 50

12/15/2018 9:56 AM

Paw Paw 271 wrote:

I see a good bit of blow by on the piston rings. The cylinder shows it is not getting a good seal to the piston ring.
I would ...more

Thanks PawPaw, I"m heading out to the garage to do some cleaning & take some measurements.

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12/15/2018 9:58 AM

dkurtd wrote:

I had an older RM with heads studs start to push water around the studs. I took the studs out and cleaned them up with a wire ...more

Agree,these studs also show some corrosion around them.. I will pull the studs out of the cylinder clean them up and surface the cylinder top, the yamabond around the studs is a good idea too, thanks for your suggestions..

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12/15/2018 10:02 AM

Not sure what to do with the cylinder...it is plated so a scotchbrite pad won't really do much...it's weird, you can clearly see the marks but cannot feel anything...

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12/15/2018 9:13 PM
Edited Date/Time: 12/15/2018 9:17 PM

the oil ratio is rich and your piston does not look like it was "compressing" water. to me

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12/16/2018 5:35 AM

barnett468 wrote:

the oil ratio is rich and your piston does not look like it was "compressing" water. to me

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40:1 amsoil dominator w/50/50 Sunoco 110 leaded & 91 non ethanol gas. The first hr of run time was with the mikuni carb that was leaking fuel internally so it was loading up/ running very rich until I swapped to a keihin carb. The last time I rode the bike was in the deep sand so I was jetted rich for safety, but the bike ran well. I did use your piston to cylinder clearance test with the folded over notebook paper! It worked good. My ring end gap is never less than .013"and never more than .015" at anywhere along the cylinder, so I think piston to cylinder is acceptable and ring end gap is acceptable. After examining the bottom Of the head gasket, I can see a few spots that appear to show a path of coolant or spent exhaust gases from the combustion chamber .....I will post a photo later on today ...thanks for your opinions...

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12/16/2018 8:04 AM

barnett468 wrote:

the oil ratio is rich and your piston does not look like it was "compressing" water. to me

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sandman768 wrote:

40:1 amsoil dominator w/50/50 Sunoco 110 leaded & 91 non ethanol gas. The first hr of run time was with the mikuni carb ...more

Glad the paper trick worked. I learned that from a guy named bill qualls back in 75 whom owned a boring shop called q & e cycle in anaheim which is still there. his son runs it now but bill still stops in once or twice a week.

It may very well have a head leak. My point was merely that it in your case, it is impossible to say definitively that it has a leak or is "compressing water" based on looking at the piston alone.

You can use a granite or marble counter top or window pane to check the surfaces for being flat although it's pretty hard to check the cylinder on a window pane. Just clan the sealing surfaces then color them with black felt pen then put a piece of 32o sand paper on the counter or window then place the cylinder or head on it then rotate it a few times then look at the colored surface. If it is not flat, there will be areas where a lot of the color remains. If the surface is not too warped you can surface it this way also but yu will likely need coarser paper like 220 and some water or wd40 on it. You can also put water on the 320 for the initial flatness check.




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12/16/2018 10:16 AM

barnett468 wrote:

the oil ratio is rich and your piston does not look like it was "compressing" water. to me

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sandman768 wrote:

40:1 amsoil dominator w/50/50 Sunoco 110 leaded & 91 non ethanol gas. The first hr of run time was with the mikuni carb ...more

barnett468 wrote:

Glad the paper trick worked. I learned that from a guy named bill qualls back in 75 whom owned a boring shop called q & e ...more

I have a nice surface plate with Emory paper taped to it to cleanup minor warpage..it works very good...I also use the sharpie marker trick to show the warpage! The head has no warpage..the cylinder top is also good, but the sleeve is slightly below the cylinder top, I,found a spot that I can get .05mm feeler gauge in using a straight edge... See photo. I removed cylinder studs & surfaced top some to get it to under .04mm which is within manual specs.... The factory head gasket is very thick ..1.35mm to be exact & has a soft metal ring that surrounds the bore, so I'm thinking with that head gasket I should be ok with the sleeve being slightly below the top of the cylinder.... Photo
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12/16/2018 10:21 AM

Few more piston photos.... Photo
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12/16/2018 10:34 AM

I will contact Powersealusa to inquire about possibly honing the cylinder before I reassemble....everything else on the teardown looked good, rod, crank bearings feel tight, reeds & intake boot were new, still look good, powervalves were still very clean & sliding nice....I did find some slight warpage on the base of the cylinder, and one of the cylinder studs into the case came out with the base nut, so it may have not been tight enough... I cleaned that up & used some blue thread locker on it....the only other think I can think of that maybe I should have I done is to retourqe the head nuts after initial break in...really if it were not for the cylinder marks, I would think everything else is normal for the hrs in the engine...

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12/16/2018 10:48 AM

sandman768 wrote:

Few more piston photos.... Photo
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"the cylinder top is also good, but the sleeve is slightly below the cylinder top, I,found a spot that I can get .05mm feeler gauge in using a straight edge..."

Ok, I for one would have the cylinder machined until it is flush with the cylinder. Shouldn't cost more than $40.00 and might take all of 10 minutes for a machine shop to do. You could also have them cut around .001" off the top of the liner if you wanted.

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12/16/2018 11:20 AM

I do have a good machine shop that I use, I will have them take a look at the cylinder walls & top....Another reason to not have a cylinder sleeved! When I had Powersealusa replate the cylinder they stated the liner was installed good, now I"m wondering........thanks again for your input...

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12/16/2018 12:53 PM
Edited Date/Time: 12/16/2018 12:54 PM

sandman768 wrote:

I do have a good machine shop that I use, I will have them take a look at the cylinder walls & top....Another reason to ...more

ah, ok, the plot thickens, however, i reread your post, and i initially thought it was .5 mm too low. .05 mm is not that bad but i would still get it machined since it is already off then maybe use a cometic head gasket or at least a factory one.

i also would not use evans coolant. regular 50/50 coolant is fine, and if you add 1.5 times the recommended amount of dei radiator relief to it, it will work even better.

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