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Post by dystopias on Jun 17, 2013 17:39:12 GMT -5
my compression was measured at 60psi, which as I understand, is too low. So I'm trying to figure out what is causing that. I tore it all apart and nothing stood out as obviously broken - but I don't really know what I'm doing - so thought I would ask for some advice. attached is a picture which shows the valves (which may or may not be closed . . .) and the piston, which had some scuffing on the top of it. I didn't know if either of these things were something to worry about. as always, your kind help is greatly appreciated. thanks, mitch Attachments:
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Post by justin010304 on Jun 17, 2013 17:45:40 GMT -5
Hard to diagnose when it is all torn down. Could have been as simple as the valves being too tight and sticking open. Could have been worn rings, or even a bad head gasket.
I can't get the picture to enlarge on my phone, but is that carbon buildup where the gasket goes? If so it may have been a bad head gasket or improperly torqued head.
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Post by scootnwinn on Jun 17, 2013 18:26:30 GMT -5
Valve is definitely open. Piston certainly scuffed. Is the cam in a position where the valve should be closed? Might as well kit it since you need a new piston and I'm guessing your cylinder matches your piston...
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Post by dystopias on Jun 17, 2013 19:15:53 GMT -5
more images: imgur.com/a/y7Ge3forgive me if I am misunderstanding - but the camshaft isn't attached to the valve in that picture, so both valves should be closed - correct? I don't see any corresponding scuff marks in the cylinder (although take a look at the pictures, it was hard to get a picture of the inside of the cylinder) this was a BBK that I installed last fall. I've ordered another one since I wasn't sure which part(s) I would need to replace and it was only $50 on ebay. (http://www.ebay.com/itm/330459445932?item=330459445932&viewitem=&sspagename=ADME:L:OC:US:3160&vxp=mtr) so you're saying I should just replace all of it? as for torque - I used a torque wrench that I picked up at an auto supply store, but it seemed to be geared to higher torque numbers than I used for this, so probably wasn't very accurate at the low end. is there a particular wrench you would recommend? |
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Post by carasdad on Jun 17, 2013 19:41:49 GMT -5
[replyingto=dystopias]dystopias[/replyingto]You are correct..both valves should be closed...but one is stuck open. You have scuff marks on the piston skirt badly...and look closely at your rings...they are scuffed as well. So your cylinder should show some scuffing also. Question is why? A bent valve stem will stick the valve open...broken or compressed valve spring can too..but you can push the valve shut.If you can't push it shut most likely it is bent. With all that carbon..it shows the engine was not run too hot and causing the damage.Therefore I would check the oil pump and oil level. Have you ever run it while low on oil or empty? Because to me...with all that damage...rings piston and valves..it leans towards an oil flow issue or lack of oil issue. Cheapest and fastest route is to re kit the engine. But DO CHECK AND VERIFY OIL FLOW! With the new kit on...leave the valve cover off..pull the plug wire so it does not fire up...then crank the engine and look for oil coming from your Rocker Arms.If after a few seconds of cranking you see no oil flow...there is a high probability your oil pump failed.  |
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Post by pmatulew on Jun 17, 2013 20:50:17 GMT -5
DX Piston, cylinder, rings, at a minimum. Looks like considerable wear. How many miles on that build?
Gotta figure out what's up with that valve and decide if the head is still okay to use.
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Post by jerseyboy on Jun 17, 2013 20:57:36 GMT -5
Yeah looks like the valve is open for sure,,
If it was all together,,you could squirt some motor oil into the cylinder and if the pressure came back up too normal 9 out of ten times its your rings,,if it don't its either valves or head gasket.
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Post by scootnwinn on Jun 17, 2013 21:04:14 GMT -5
Looks like the whole top end is done for actually that valve though is likely your compression issue though...
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Post by dystopias on Jun 17, 2013 21:09:32 GMT -5
[replyingto=jerseyboy]jerseyboy[/replyingto]just an estimate here, but i would say about 400 -450 miles on that. don't know if it matters, but when i took it apart there was oil under the valve cover. i can't get the valve to close any more by pushing on it.
again, I'm still learning about all of this, so please excuse the following question, which may sound rather ignorant -
could this have anything to do with the jets on the carb? when I went from 50cc to 100cc i didn't do anything to them and some people have suggested that I should have . . .
thanks again,
mitch
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Post by carasdad on Jun 17, 2013 21:09:56 GMT -5
DX That valve is bad Mojo...how you even got 60psi is beyond me with that valve opened up that far...  |
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Post by jerseyboy on Jun 17, 2013 21:12:55 GMT -5
[replyingto=dystopias]dystopias[/replyingto]You may have got it way too hot with a LEAN condition,,was it popping/backfiring through the exhaust on decel?
What did the plug look like,,really light in color?
Probably needed to up jet and get more fuel in there to keep things cooler and running right.
JMO
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Post by scootnwinn on Jun 17, 2013 21:13:06 GMT -5
Yes you should have up jetted you ran too lean and that is the result. Read every build on this board before you go forward. I thought too lean from the first post...
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Post by alleyoop on Jun 17, 2013 21:14:43 GMT -5
Looking at the piston top unless the carbon fell off where it is still shiny that side was not torqued correct. Looks like that whole side of the head was not torqued correclty. Need to tighten them up just nice and snuge EVENLY CRISS CROSS Top Left-Bottom Right Top Right- Bottom Left then TORQUE in the same sequence to 18Ft LBS.
Alleyoop
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Post by dystopias on Jun 17, 2013 21:21:52 GMT -5
[replyingto=jerseyboy]jerseyboy[/replyingto]No, i've never heard any popping/backfire.
as for torque, what kind of torque wrench would you recommend?
i'll deff. read more posts on this, tried my hardest to follow instructions well last time.
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Post by hank on Jun 17, 2013 21:28:41 GMT -5
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..BAD TO THE BONE..