new top end rebuild question

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snowrocket

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new top end rebuild question..HELP!!!!!!!

End gap seemed good with a .356 mm feeler going in with no resistance at all and the piston mic out at correct dia.When at t.d.c. the piston seems to have a lot of play (BACK AND FORTH) but the cylinders DIA. mic out at middle of spec. It almost sounds like the piston is hitting the cylinder wall as i push back and forth on it. doesnt seem normal with a new top end rebuild. was about to put head on when i noticed it It just seems like the piston is moving side to side not the ring. Should the piston be able to touch the cylinder side wall at all. My concern is that the piston may slap the side wall to much during operation. everything measures correct so by this it should be ok but not sure.
 
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Did you assemble the motor dry? Meaning that you did not lube the piston before installing into the cylinder. There is supposed to be a little play between the piston and cylinder wall as the piston will swell under normal operation and the bore will also swell some too, plus there needs to be some room for the oil to displace so that the motor doesn't seize.

From what I can figure, you have about .014" of clearance which may be a little big(dont have my manual handy). The bores in the cylinders should not vary in size as they are bored with no taper. If your bores are out of spec you will need to send your cylinders out and have them replated... How many miles on this motor???
 
yep coated the rings and piston and cylinder walls etc...the play is not excessive but just felt a little more than usual. The bores are new coated and spec out great all the way through. The lower I just bought from a buddy that recked his last year and had 2000 miles on and so i just decided to do the top end anyway as originally i was going to put in a 780 kit but decide not too after apart. I used winderosa gaskets....have you heard any bad things about them. I read on TY that they have some issues but I have always used them in years past and have never had issues but did not know if somthing has changed.
 
I guess if everything measures in spec then you should be good to go... Have heard complaints about windrosa gaskets but have never used them, have always used either oem or cometic.
 
you dont want too much free play but...geez ive ran my cr250 with the whole crown of the piston on the front exhaust port broken...chewed ..and spit out and it took the front part of the rings and all and it ran me home 9 miles. and i re-used that cylinder... it was pretty messed up its nikaseal too. still runs today...my opinion re-sleeve with cast-iron instead of nikaseal...no re-plate expensiveness.. with cast just bore it out grab a oversid piston..............oh is spi a good piston brand ive never used them?thanks
 
There is a reason why the cylinders are nickasil plated and not a steel bore... A steel bore does not dissapate the heat like a coated aluminum bore, PLUS the coating is much tougher and slipery-ier than a raw steel or cast iron bore, there is also a potential problem with dissimilar metals and expansion rates and electrolosis.
 
i put the head on and torqued just to see and yea i have blow by. Can hear it coming out of the exhaust ports. i would not think you should have any blow by even before break in.
 
Okay..... Did you put a compression tester on it to see how bad??? You will have some blow by as the rings still need to seat and "get to know its new neighbor". This is one of the reasons they say to run the engine easy for the first tankful of fuel as the motor needs time to "break in".

You did say that the pistons measure correctly and so do the cylinders, right??
 
yes..I had the tester on it and it came up to 30 psi. The only thing i am wondering is the end gap was a little on the small side at .014 ( feeler went in but a little snug ( cold though was about 45 in garage that day) I am debating taking it back apart and opening the gap and putting a new oem base gasket on it? since we have no snow i have time...and we have no snow!!!!!!! :letitsnow
 
I set my ring end gap a lot higher than that, but my bore was bigger. I went on the big side of the spec, too... .022-.024 for mine, with a 74.8 mm bore. I think wiseco was calling for .018. They also called for .0025 piston to wall clearance and mine is set up at about .0035.

If it's loose, nobody knows... if it's tight, everybody knows!

I wouldn't worry about leakdown until it's broken in.
 
Dave your piston to cyl clearance is only 2 1/2 - 3 1/2 thousandths(is that overall or per side)? Where as rockets "seems" to be larger for a smaller bore(the way I took it). Somethings not right.... If rocket only has 30psi compression on new pistons and rings and all of that slop that he talked about then "something is wrong in Denmark", I think he may be getting confused between english and metric conversions... If your ring end gap is a little tight that won't hurt much if anything as the bore will swell with operating temperatures, and yes the piston and rings will swell also if your ring end gap was extremely tight the rings will not fit the bore as the ends will touch.
 
ok...the .014 i talked about was (IN.) the feeler gage has both in/metric. My Yam. book calls out .014 to .022 for end gap. I went ahead and poped off one cylinder ( gently ). When cold ( 40) in garage i could not get the .014 feeler to go in but could get a .012 with no problem and a .013 with slight force. Not sure if I should just leave it and put the cylinder back on ( if I can as it was only torqued down for a week) the base gasket ( winderosa) measured .025 after torqed. I have never in the past had to do this so not sure if it will seal up or not? My guess is take the other two off and put new gasket on and call it good. My rings are Wesco and I in the past have not had to open up the gap on rings so is it that they run the end gap smaller now so the customer can adjust if needed? also now that i have the motor out of the sled again is there a way to check comp. on the bench.
 
I would open up the rings just a little bit. If the spec is .014-.022 I'd run them on the high side, closer to .022. If they heat up and contact each other they can grab a port or bind in the bore. Maybe it's unlikely, but better safe than sorry in my book.

And don't worry about reusing the gaskets. You can get a few uses out of them if they don't get damaged. Just make sure you pressure test it when you put it back together. If you're concerned, buy some of that spray copper stuff and it'll make those gasket seal up just fine. If the motor hasn't been run, you could put it together with those gaskets, pressure test, and if there's a leak pull it back apart and then use the spray copper. But a lot of time's I'll just use the spray stuff on new gaskets anyway, because I know they'll seal up good that way.

Bandit, yes my piston to wall clearance is speced by wiseco at 2.5 thousanths, and that's total. That spec is low, in my opinion, because forged pistons especially will expand more with heat than the cylinder will (also because they're hotter than the cylinder). So mine are set around 3.5-4 thousanths. The first time I put the motor together they were measured with a fancy bore gauge and honed out to about .0036-.0037 (if memory serves correct). However I caught a ring on the exhaust port and had to replace a cylinder. So I had both honed out, and my friend that does the work had his bore gauge setup for some banshee work he was doing, so he did it by feel and checked it with a snap gauge. The one that was re-honed obviously got a little bigger, so it's probably closer to 4 thousandths. He used a snap gauge and a micrometer to measure the new one and it was at about 2.5-3, so he honed about another thousandth out and it ended up feeling about the same as the other one. So, they're both at about 3.5-4, which should be about right. I'd be uncomfortable running it as tight as wiseco suggests. I think on my waverunner I'm running that kind of clearance with a cast piston, but it's been a while so I don't remember the exact numbers. That's a bigger bore with a much greater ability to cool the cylinder, though.
 
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snowrocket said:
ok...the .014 i talked about was (IN.) the feeler gage has both in/metric. My Yam. book calls out .014 to .022 for end gap. I went ahead and poped off one cylinder ( gently ). When cold ( 40) in garage i could not get the .014 feeler to go in but could get a .012 with no problem and a .013 with slight force. Not sure if I should just leave it and put the cylinder back on ( if I can as it was only torqued down for a week) the base gasket ( winderosa) measured .025 after torqed. I have never in the past had to do this so not sure if it will seal up or not? My guess is take the other two off and put new gasket on and call it good. My rings are Wesco and I in the past have not had to open up the gap on rings so is it that they run the end gap smaller now so the customer can adjust if needed? also now that i have the motor out of the sled again is there a way to check comp. on the bench.
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Okay, I know what you are saying with the feelers having in/metric on them. Go to your local auto parts store o'reilleys, napa, advanced auto and ask for permatex gasket spray tack , or there is another version of this product that is brush on and comes in a small metal can with a brush applicator cap(believe it is called gasket tack). This will help with making sure the gaskets seal. You should be okay if you open up the motor again and recheck your steps just be sure that you don't rip or tear any of the gaskets.

Now when you did the work between cylinders and pistons are the pistons made by wiseco also? I am just making sure that you didn't mix and match parts... If so good. Wiseco pistons run a bigger tolerance than the stock cast pistons as the forged pistons tend to swell more than cast ones. 2 thou difference on the end gap isn't a big deal, I like to set my stuff up a little bit tight. If you set the end gap up large now you will wind up with more blow by later as the gaps will go out of spec quicker meaning that a larger ring end gap now is closer to your maximum wear limit. Remember that is what your tolerances represent in your manual is wear limits and not set ups.

Do you mean to check comrtession on the bench by pulling the motor over? Sure it can be done on the bench but you will have to be careful and you may need another set of hands. Also make sure that the plugs are out of the other cylinders.
 
There are 2 things to think about when setting things up. If it's as tight as it can be without damaging the engine, you will make the most power. However, if you go too tight, or overheat, or lean, you're more likely to toast the engine. If you set it up a little loose, you have a greater margin for error before you sieze the motor if you go a little lean or run a bit hot, or just hop on it and ride without letting it warm up properly. Yes you're closer to the wear limit, but in most cases that limit is just a suggestion anyway. There's no reason you can't exceed the wear limit on things like ring end gap and piston to wall clearance as long as the parts are still in good condition. It won't make as much power, and you'll give up a little bit of efficiency, but it'll still run.

I just want my shit to run and be fun to ride. I'm willing to give up a little bit of HP for that. If I had a bigger budget, unlimited time to work on it, and some actual freaking snow to ride it in, I might set things up on the tighter side of the tolerance and do all the testing / tuning for maximum power. As it is, though, I just want a reliable motor, slightly rich carb tuning, and clutches that work well even if they're not perfect.
 
Thanks for the input gents. As this is not the first time rebuilding engines etc..but it is the first in about 17 or so years so i appreciate the feed back. i will take back apart and inspect the gaps etc. I also ordered a new base gasket just incase i damage the old one. I just can not get over the wide clearences these engines have. When i use to rebuild the top end on my Honda 250R it was much tighter and my honda 200x (4 stroke)after adding a big bore kit was alot tighter too seemed anyway. Sure would like some snow so i can break it in before putting away for spring. :letitsnow
 
Clearances are generally dependant on piston and cylinder material, and are generally expressed as a certain # per inch of bore. So a larger bore will have a larger clearance because there is more material to heat up and expand. Also, a forged piston will expand more with heat than a cast or hypereutectic piston so they will require more clerance as well. Another important factor with forged pistons is warm up - you want the cylinder and piston to warm up gradually. If you start it up and start beating on it, the piston can get hot before the cylinder, causing it to expand into the cylinder walls and sieze.

And I hear ya on the snow! I just got my vmax back together, and rode it once. Played with the carbs a little, but the clutches are fubar and I will need some time on the ice or snow to get those close and tweak the carbs a little better. I spent a bunch of time in the fall and all winter dicking with it, and I have hardly ridden the damn thing!
 
Had to replace base gasket as the old ripped when taking ofF last cylinder. I got my new metal one but there are 2 of them so do I spray gasket tact on both( i assume ).
 
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