New rebuild, compression issues, got questions.

[Walleye]

I got 65.5mm wiseco pistons, and the box says 2.579 bore is needed for ring clearance, well when i got the jugs bored and honed, it was exactly 2.579, and i checked the bottom of the piston skirt, and it read, i forgot the exact number, it was 2.573 or 2.574, so i figured it was fine, and its how wiseco set it up. so i installed it, and did a compression check before starting it, and it was btw 105 to 110 psi. i ran it for a while like 15 - 30 mins and let it cool then another run same lenth down the road. outside temp of the jugs with temp gun read around 13x degree.

 

i rechecked the compression after letting it cool down completely a hr or so later, it reads only about 115 to 117psi.

 

my question is for others who rebuilt with wiseco pistons, did you do compression test before first fire, and then another one after a good run? or check it after breaking it in?

 

what is the proper compression supposed to be with 65.5mm bore and .030 shaved head? thats what i have.

 

My last rebuild with 65.25mm yeild out 135psi and i rebuilt it again after 10-12hrs of hard ridding because i wanted it to be between 160 to 180 psi like other friends have in their 250r and cr500. plus my bore was .003 over when i put in the 65.25mm pistons.

 

 

now the bore is exactly 2.579 but the skirt reads smaller. so am i supposed to run it for a good few hr or a tank to allow the pistons to thermal expand?

 

or is it not correctly setup? and should i remove the pistons and contact wiseco and get another piston replaced since the bottom of the skirt is not 2.579" which its supposed to be at.

[RILS]

I got 65.5mm wiseco pistons, and the box says 2.579 bore is needed for ring clearance, well when i got the jugs bored and honed, it was exactly 2.579, and i checked the bottom of the piston skirt, and it read, i forgot the exact number, it was 2.573 or 2.574, so i figured it was fine, and its how wiseco set it up. so i installed it, and did a compression check before starting it, and it was btw 105 to 110 psi. i ran it for a while like 15 - 30 mins and let it cool then another run same lenth down the road. outside temp of the jugs with temp gun read around 13x degree.

 

i rechecked the compression after letting it cool down completely a hr or so later, it reads only about 115 to 117psi.

 

my question is for others who rebuilt with wiseco pistons, did you do compression test before first fire, and then another one after a good run? or check it after breaking it in?

 

what is the proper compression supposed to be with 65.5mm bore and .030 shaved head? thats what i have.

 

My last rebuild with 65.25mm yeild out 135psi and i rebuilt it again after 10-12hrs of hard ridding because i wanted it to be between 160 to 180 psi like other friends have in their 250r and cr500. plus my bore was .003 over when i put in the 65.25mm pistons.

now the bore is exactly 2.579 but the skirt reads smaller. so am i supposed to run it for a good few hr or a tank to allow the pistons to thermal expand?

 

or is it not correctly setup? and should i remove the pistons and contact wiseco and get another piston replaced since the bottom of the skirt is not 2.579" which its supposed to be at.

Im going to try to anwser this.I think you are in the ball park with your clearace,you will get a better reading after your rings have seated completly.As for your compression you said yourebuilt to get it higher this is where im confused.What elevation are you at?I would guess if you shaved 30thousands off you should be between 130 and 150 depending on elavation.If you want to go higher than that the easiest and best way would be to get a aftermarket head and the domes to get you where you want to be.Keep in mind if you get around 160 or higher you will need to run atleast 106octane or better.But why would you rebuild after only 10 hours for compression reasons , at that time you were just getting it broke in good?

[brilei5]

The first thing I would do is check the gauge. Borrow a freinds or buy another. They do go bad. Depending on elevation 0-1000 feet above sea level your compression should be around 130-140 with the shaved head. I have had compression go up slightly after break in, but I am talking 177 going up to 180. Are you doing the test with the fuel on-- throttle open-- and kick it until the gauge will not go any higher? That is what I do. If it is still low. I would start checking things like o-rings or head gasket. Also you did not mention any Port work. But port work can effect the static compression. i.e. the same size engine with different size exhaust ports can have different compression readings on the gauge but the same compression ratio.

[Walleye]

Im going to try to anwser this.I think you are in the ball park with your clearace,you will get a better reading after your rings have seated completly.As for your compression you said yourebuilt to get it higher this is where im confused.What elevation are you at?I would guess if you shaved 30thousands off you should be between 130 and 150 depending on elavation.If you want to go higher than that the easiest and best way would be to get a aftermarket head and the domes to get you where you want to be.Keep in mind if you get around 160 or higher you will need to run atleast 106octane or better.But why would you rebuild after only 10 hours for compression reasons , at that time you were just getting it broke in good?

 

 

I am at like about 500-700ft elevation.

 

the reason i rebuilt it is because the first rebuild, the bore was .003 too big, and i only got 135psi so i thought why not get next bigger bore wiseco has from 65.25 and make it 65.5 and get the bore exactly right to the requirement for ring clearance which is 2.579" and hope to get the correct psi which i thought would be 160 or more since my other friends have 160-180 on their other 2stroke atv or dirtbikes. but im not sure what the stock psi is on the banshees.

 

 

I have only run a few laps on the road with the most recent rebuild, and its only showing 115psi while the last one showed 135psi. so i was seeing if that is pretty right and needs to break in more in order to get more psi increase.

 

but i guess i will have to run it more and check again. but my concern is that the piston bottom skirt only showed 2.573 or 4 so thats pretty much .005-.006 under what the ring requirement is. So i was thinking i know that does make a big difference to the psi, than if the pistons were at 2.579 and the bore was at 2.579 it would show up more psi than 115psi.

 

So my question is what psi should i be getting and if i should return these pistons before i put any more wear on it and get the correct skirt sized pistons. or should i just risk it and break it in longer and thenc heck it again?

 

The first thing I would do is check the gauge. Borrow a freinds or buy another. They do go bad. Depending on elevation 0-1000 feet above sea level your compression should be around 130-140 with the shaved head. I have had compression go up slightly after break in, but I am talking 177 going up to 180. Are you doing the test with the fuel on-- throttle open-- and kick it until the gauge will not go any higher? That is what I do. If it is still low. I would start checking things like o-rings or head gasket. Also you did not mention any Port work. But port work can effect the static compression. i.e. the same size engine with different size exhaust ports can have different compression readings on the gauge but the same compression ratio.

 

 

i did it only with throttle open, will need to try with gas on, but i have the tank off when doing the compression check since its much easier to install the gaue that way.

 

only port work i have is knife edged intake dividers, and polished the exhaust ports. thats all.

 

i'm going to recheck the torque. also my H22A1 engine in my Civic shows 225psi all over the 4 cylinders. i have no other gauge to try out, will need to buy.

[RILS]

I am at like about 500-700ft elevation.

 

the reason i rebuilt it is because the first rebuild, the bore was .003 too big, and i only got 135psi so i thought why not get next bigger bore wiseco has from 65.25 and make it 65.5 and get the bore exactly right to the requirement for ring clearance which is 2.579" and hope to get the correct psi which i thought would be 160 or more since my other friends have 160-180 on their other 2stroke atv or dirtbikes. but im not sure what the stock psi is on the banshees.

I have only run a few laps on the road with the most recent rebuild, and its only showing 115psi while the last one showed 135psi. so i was seeing if that is pretty right and needs to break in more in order to get more psi increase.

 

but i guess i will have to run it more and check again. but my concern is that the piston bottom skirt only showed 2.573 or 4 so thats pretty much .005-.006 under what the ring requirement is. So i was thinking i know that does make a big difference to the psi, than if the pistons were at 2.579 and the bore was at 2.579 it would show up more psi than 115psi.

 

So my question is what psi should i be getting and if i should return these pistons before i put any more wear on it and get the correct skirt sized pistons. or should i just risk it and break it in longer and thenc heck it again?

i did it only with throttle open, will need to try with gas on, but i have the tank off when doing the compression check since its much easier to install the gaue that way.

 

only port work i have is knife edged intake dividers, and polished the exhaust ports. thats all.

 

i'm going to recheck the torque. also my H22A1 engine in my Civic shows 225psi all over the 4 cylinders. i have no other gauge to try out, will need to buy.

In my opinion you are no offense but pissing in the wind messing with the pistons oner that clerance,I agree it could be a little tighter but,you have to have some for the ring,and if thats what they recommend you should be fine.On that same note ur rings have more to do with holding compression than your pistons,for example if your bore was exactly the same size as your pistons you would never getthe piston in, Thats where the clearance and ring come into play.If you like to have your pistons tighter than that I would take the pistons to the shop who does the bore and ge them bored maybe a little tighter,but they do expand and you can file the ring to fit.If you were at 135 and now your at 115 I say you have something else going on like a oring or something leaking.Like I said before if you want to run 160psi get a noss head with 20ccdomes if you want 170 get 19cc domes if u want 180 get 18cc domes and be done with it,you could have done this without boring proably with less money and got ur compression at what ever you want with just the change of the domes at any time.

Edited June 10, 2006 by RILS

[brilei5]

As far as the piston to wall clearence goes. On Forged pistons, wich is what Weisco's are. you should hone to .002-.003 clearence. You have .005-.006 that would affect compression a little bit. BUT in my experience, I notice about a 10% decrease in compression when piston to wall gets to around .008-.010. Thats when I know I need a rebuild. Who ever bored your Cylinders may have gone too big in my opinion. Any machinest should mic the piston and then bore and hone to the correct tolerance.

[dlnoss]

Make sure the compression tester threads into the spark plug hole the same depth as the spark plug. If not, you will get a false reading. Some of the testers only thread in 3/8" to 1/2" which displaces less volume in the combustion chamber giving false (low) readings.

[RILS]

Make sure the compression tester threads into the spark plug hole the same depth as the spark plug. If not, you will get a false reading. Some of the testers only thread in 3/8" to 1/2" which displaces less volume in the combustion chamber giving false (low) readings.

This is true.

[Walleye]

okay guys i think your getting what im saying wrong in some areas, but thats ok, ill clarify it a bit.

 

i bought my banshee with bad compression like 90 psi, bought 65.25mm pistons, got it bored and honed but it was .003 bigger than what the ring clearance requirement on the box of teh pistons stated from wiseco, 2.569, which the bore of jugs, it measured 2.572 after bore and hone. the 65.25mm pistons at the bottom shows 2.569. i decided it was ok, and rode 10-12 hrs of hard abusive ridding, and the compression after 2 hrs ish of break in showed 135psi.

 

 

now i thought that since it was .003 overbore than what wiseco specs are, that was the reason i wasnt getting anywhere close to 160 psi. so i decided to get 65.5mm pistons and re do the bore and make sure its exactly 2.579. it turns out when i got the jugs back it was exactly at 2.579"

 

keep in mind this is my 2nd rebuild. before installing the pistons i measured the bottom of the skirts which i try and remember the numbers which is lower, around 2.573 to 2.574 on the bottom of the skirt on pistons.

 

i decided that it was how wiseco did it, and installed it anyways and thought the heat will thermally expand the pistons.

 

 

but now im thinking if my 1st rebuild the bottom of the skirt on the 65.25mm pistons read 2.569 and then why does the 65.5 mm pistons read .005-.006 smaller than what the number on the box of the piston box stated (which is 2.579). so i figured that those pistons i got were manufacturing mistake, so im not sure if it is, or its how wiseco did it specifically.

 

also i just spoke with my friend a few min ago letting him know what the updates are on my thread, and i told him that some people here stated that anything over 160psi is not safe on pump gas. his CR500 has almost 180psi and hes running 93 octane and 40:1 mix ratio. and its been fine since, and hes getting 160ish psi on his TRX 250R and running 40:1mix ratio on 93 octane.

 

we were wondering why 160 or over is not safe on pump gas while my car motor, which is 2.2l DOHC 4 stroke is showing 225psi on each 4 cylinders and i am running 93 octane. it doesnt make sense to us in some way.

[RILS]

DETONATION.It will ruin your motor tell ur budd to put some 110 octane in and see if it sounds the same.Id like to see the pistons in that cr on 160 u might get by with a 50/50 93/110 mix.If you dont want to run high octane there is no need to raise the compression that high.

[Walleye]

Make sure the compression tester threads into the spark plug hole the same depth as the spark plug. If not, you will get a false reading. Some of the testers only thread in 3/8" to 1/2" which displaces less volume in the combustion chamber giving false (low) readings.

 

 

i just ran out in the garage and checked and its the same length.

 

DETONATION.It will ruin your motor tell ur budd to put some 110 octane in and see if it sounds the same.Id like to see the pistons in that cr on 160 u might get by with a 50/50 93/110 mix.If you dont want to run high octane there is no need to raise the compression that high.

 

 

its stock compression, just at its last bit of bore size wiseco offered, nothing was done to increase the compression.

Edited June 10, 2006 by Walleye

[RILS]

i just ran out in the garage and checked and its the same length.

its stock compression, just at its last bit of bore size wiseco offered, nothing was done to increase the compression.

Ive never had a motocross bike with stock compression that high and ive had a few.If you choose to run 180psi on 93 good luck but i feel you will lean a lesson the hard way.I would say your buddy has been lucky to still be running.Bore size has nothing to do with compression when you here that ping its not good.

[Walleye]

Ive never had a motocross bike with stock compression that high and ive had a few.If you choose to run 180psi on 93 good luck but i feel you will lean a lesson the hard way.I would say your buddy has been lucky to still be running.Bore size has nothing to do with compression when you here that ping its not good.

 

 

well it does not ping at all, hes a member at cr500riders.com forum and other people there that have 180 psi and dont ping and run just fine on 93 octane.

 

if 160 or higher isnt good then why is it ok with my honda motor running 225psi on stock motor and 10:1 cr on 93 octane, that part is confusing me.

[RILS]

well it does not ping at all, hes a member at cr500riders.com forum and other people there that have 180 psi and dont ping and run just fine on 93 octane.

 

if 160 or higher isnt good then why is it ok with my honda motor running 225psi on stock motor and 10:1 cr on 93 octane, that part is confusing me.

180 psi is not 10;1 its more like 12.5;1 and its not allright to run a honda at225 thats over14;1 on 93 go to your nearest race track nascar dirttrack dragstrip or anything even your local grease monkey and see how many of them run 93 on a motor with that kind of compression.I didnt say it wouldnt run i said it will damage it and it will spark nock "ever heard of this".If it was ok you would see the whole nascar field filling up at the local bp instead of hauling aroun sonco and all the other expensive race fuels.

[Walleye]

180 psi is not 10;1 its more like 12.5;1 and its not allright to run a honda at225 thats over14;1 on 93 go to your nearest race track nascar dirttrack dragstrip or anything even your local grease monkey and see how many of them run 93 on a motor with that kind of compression.I didnt say it wouldnt run i said it will damage it and it will spark nock "ever heard of this".If it was ok you would see the whole nascar field filling up at the local bp instead of hauling aroun sonco and all the other expensive race fuels.

 

 

when i stated 225psi, i was talking about my 1993 Honda Prelude H22A1 2.2L DOHC VTEC 4 cyl motor, its stock compression is 10:1 and i just checked the compression and the max i saw on one cylinder was 225psi, it was from 217 to 225 on all 4 cylinders. and i spoke to other people on a honda forum where its a well known place and most H22A owners run 190 to 230psi and those motors run on 93 octane, why cant 2 stroke run on pump gas (93 octane) above 160psi?

 

I've built Honda auto motors before a few times and those psi are about right.