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CR 250 Piston Blow By and Ring Condition ?

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Hello, the pictures I am posting below are of the piston and cylinder wall on my 2003 CR250R. I just put the LA SLEEVE 270cc Big Bore kit. The pictures are taken from the exhaust port and I would say that the new sleeve, piston and rings have approximately 8 hours on them. My question is I am seeing blow by that goes down past the second ring and worried if this is normal or acceptable. I followed the LA SLEEVE break in procedure exactly. I have been running the premix 32 to 1 instead of 40 to 1 could that cause this. Just a little worried because this is the second new sleeve and piston in 3 months. I am pretty sure the first failure was caused by my son riding it with a damaged radiator that was loosing coolant and blocking the flow of the coolant. I have since then went with new oversized radiators and fixed that problem. Please let me know what you think... I appreciate it.IMG_20130711_215601_951.jpgIMG_20130711_215827_787.jpgIMG_20130711_215835_711.jpgIMG_20130711_220145_630.jpgIMG_20130711_220356_197.jpg

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I did and it was within specification unless I measured incorrectly. I used a digital measuring caliper that I bought a Advanced Auto Parts store... Not top of the line but I assume it is accurate.

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Ring end gap is measured by inserting the rings into the cylinder without the piston and measure the gap with a set of feeler gauges. Sounds like you just measured the open end ring gap.

I don't know why it would be too big if it was all new and the correct parts. Normally its too small and you have to file some away but if for some reason it was way too big it could be causing the blow by.

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I do not even change my rings or ever even worry about them. If your rings are shot, you have bigger things to deal with. It is time for a new piston kit at the least. and possibly a replate.

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That's a lot of blow-by for an 8 hour engine. Did you oil the new piston and rings when you built the engine? That will promote cylinder glazing and increase ring blow-by. An easy break-in it does it too.

I wouldn't run out and buy a new piston. If it measures in spec, it's good. You do need a new set of rings.

Edited by CamP

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If the rings were in spec (or close) when you first installed them and they are already shot after 8 hours you could have some bigger problems to deal with like dirtjumpordie said.

I don't really know much about the la sleeve but i'm guessing they supplied you with a matching piston and ring kit. Yes?

Edited by GaDRZ400sMan

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I did not measure the rings in the cylinder without the piston but saw that I should have while searching earlier today. I will do that next time. My question is do you think it is to much blow by or something that I should be worried about. Part of the problem is that it is the 270 kit and I have to rely on what LA Sleeve recommends. Like I say this is a brand new build and has no marks or scoring on the piston walls or cylinder. I runs awesome I am just worried about the blow by, should I be worried about it?

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That's a lot of blow-by for an 8 hour engine. Did you oil the new piston and rings when you built the engine? That will promote cylinder glazing and increase ring blow-by. An easy break-in it does it too.

Yes, I for sure over oiled it thinking the more the better, I guess not, it was like a stick of butter when I put it in. Do you think that is what caused it. I put a lot of Lucas premix on the cylinder rings and sleeve before I put it together.

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If the rings were in spec (or close) when you first installed them and they are already shot after 8 hours you could have some bigger problems to deal with like dirtjumpordie said.

I don't really know much about the la sleeve but i'm guessing they supplied you with a matching piston and ring kit. Yes?

Yes LA Sleeve supplied the correct piston and ring set for the big bore.

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So it sounds like I need a new set of rings, today starts my vacation and was planning on woods riding the next 3 days, will I be harming anything by riding it as is and replacing the rings after the week of riding?

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Did you install the sleeve or did LA Sleeve install it. I was reading on their FAQ and it says its a semi-finished bore when they send it out. If they did all the work then its no problems.

Here is the FAQ: http://www.lasleeve.com/technical

Yes LA SLEEVE did all the work and supplied the Wiesco piston and rings that they recommend. They also machined the RC valve for the bore. This is the first bike I have ever worked on with the electronic RC power valve, if I did not adjust the cables correctly could that cause the symtoms in the pics. It does run awesome... am I being paranoid?

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looks like my old piston shortly before it cracked at the exhuast bridge (that one lasted 6hrs). is it burnt on the top? are you running with a lean condition?

being as paranoid as i am now, I would atleast re-ring and bump my fuel quality. I had pinging issues with my head being lowered. was over in the sand dunes last weekend, ran 40:1 on 50/50 premium/VP110 and it felt strong. will pull the pipe soon enough to get a look at the piston.

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Yes, I for sure over oiled it thinking the more the better, I guess not, it was like a stick of butter when I put it in. Do you think that is what caused it. I put a lot of Lucas premix on the cylinder rings and sleeve before I put it together.

Blow-by is too be expected if you heavily lubed the piston/rings when you built the engine. Buy a new set of rings and assemble the piston and rings dry. Don't baby the engine when breaking in the new rings. Thoroughly warm up the engine, take one easy lap, then hammer it hard.

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I don't like the idea of dry assembly. I learned from a very respected engine builder (car engine builder) that you can use WD40 while assembling an engine. It is a solvent so I use it to clean the bore, then I spray a film on the cylinder and the piston while assembling. It is a thin oil so it won't glaze your cylinder. I don't like the idea of my piston going at 2000 rpm until enough lube gets in there to lube the piston and bottom end. It also helps to ignite the engine for the first time too.

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I don't like the idea of dry assembly. I learned from a very respected engine builder (car engine builder) that you can use WD40 while assembling an engine. It is a solvent so I use it to clean the bore, then I spray a film on the cylinder and the piston while assembling. It is a thin oil so it won't glaze your cylinder. I don't like the idea of my piston going at 2000 rpm until enough lube gets in there to lube the piston and bottom end. It also helps to ignite the engine for the first time too.

A light film of WD40 is fine, just wipe off any excess with a paper towel. As soon as the engine fires, it's getting sufficient lube from the fuel. In 35 years of building 2-stroke engines, I've found that the dry build has no down sides, but if you sleep better with a little WD40 on the piston, it won't hurt anything. The last thing you want to do is put pre-mix oil on the piston, rings and/or cylinder.

Edited by CamP

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Ok guys, a lot of helpful hints and I will for sure not use a half gallon "Ha Ha" of pre mix on the cylinder and walls when I install the next set of rings. I just want to know if anyone thinks I will be damaging any thing if I ride in for 3 or 4 rides as is before tearing down and putting the new rings in. Also if the cylinder and piston walls are glazed, how do I fix that.

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