Olds Eddie Posted May 24, 2007 Report Posted May 24, 2007 I have checked everything I know to ckeck and after totally redoing my top end with Wiseco Pro Light pistons I still have low compression (60-67). I checked it with a known good compression checker and no carbs installed. I have the right pistons installed correctly and re-honed the cylinders. Engine has not been started yet since I fitted new rings and reassembled it. Will reeds cause low compression? Any other ideas? Quote
fastrthnu Posted May 24, 2007 Report Posted May 24, 2007 do you have access to a leak down tester? could be leak in in the head. reeds will sometimes mess with compression, but not that much. Quote
Bansh-eman Posted May 24, 2007 Report Posted May 24, 2007 you said you did a compression test with no carbs? Thats an issue right there.. to do a compression test you need your carbs and pipes on. remove one spark plug and install the tester. with the start botton turned to off. hold the throttle wide open and kick it over until the needle stops moving. thats your compression for that side. do the same for the other side. Quote
blowit Posted May 25, 2007 Report Posted May 25, 2007 you said you did a compression test with no carbs? Thats an issue right there.. to do a compression test you need your carbs and pipes on. remove one spark plug and install the tester. with the start botton turned to off. hold the throttle wide open and kick it over until the needle stops moving. thats your compression for that side. do the same for the other side. Carbs and pipes are not needed for static comp testing. The reeds should be installed though. If you are that now on comp with the reeds on, better do some lookin around. Brandon Quote
Bansh-eman Posted May 25, 2007 Report Posted May 25, 2007 Carbs and pipes are not needed for static comp testing. The reeds should be installed though. If you are that now on comp with the reeds on, better do some lookin around. Brandon you know what, iv never even thought of it but your right you dont. either way your getting the max compression with it carbs or not casue its not leaking out. Quote
blowit Posted May 25, 2007 Report Posted May 25, 2007 I have checked everything I know to ckeck and after totally redoing my top end with Wiseco Pro Light pistons I still have low compression (60-67). I checked it with a known good compression checker and no carbs installed. I have the right pistons installed correctly and re-honed the cylinders. Engine has not been started yet since I fitted new rings and reassembled it. Will reeds cause low compression? Any other ideas? Crap, sorry, I am replying to the wrong people here. Yes, your reeds can affect static numbers by not allowing crankcase pressure to be formed. That is needed to force air to the combustion chamber. If you have damaged reeds, you might take a closer look. Also, please let us know what comp tester you are using or even give us a pic of the very end that is threading into the head. That fitting MUST have a valve in it for accurate testing. Brandon Quote
Olds Eddie Posted May 25, 2007 Author Report Posted May 25, 2007 (edited) Crap, sorry, I am replying to the wrong people here. Yes, your reeds can affect static numbers by not allowing crankcase pressure to be formed. That is needed to force air to the combustion chamber. If you have damaged reeds, you might take a closer look. Also, please let us know what comp tester you are using or even give us a pic of the very end that is threading into the head. That fitting MUST have a valve in it for accurate testing. Brandon Thanks for the reply. I am using a Snap-On comp tester with valve at the guage. I used it on my sbc 400 in my fishin' boat to see if it was accurate and it seemed to be. I have done everything I can think of but replace the reeds. One of them has a burned spot on it that can be seen through the carb spigot, so that is why I suspect it is reeds.Will reeds make the compression that low? (57-65psi) Edited May 25, 2007 by Olds Eddie Quote
Satsol67 Posted May 25, 2007 Report Posted May 25, 2007 What is your ring gap? Are you sure you used the right pistons??? If ring gap and pistons are right see if it is leaking around your head. It can only be a few things. Quote
Olds Eddie Posted May 25, 2007 Author Report Posted May 25, 2007 What is your ring gap? Are you sure you used the right pistons??? If ring gap and pistons are right see if it is leaking around your head. It can only be a few things. Ring gap is within spec. (.30-.45mm) I filed and chamfered them myself. Head gasket has been re-done 3 times since I started this investigation. What else can it be. It ran great before I did some wiring and wouldn't restart afterwards. That's when I checked the compression. It had been leaking unfiltered air around the filter which took out the fresh rings. I honed and re-ringed her and still low compression. I'm stumped! Quote
blowit Posted May 25, 2007 Report Posted May 25, 2007 What is your ring gap? Are you sure you used the right pistons??? If ring gap and pistons are right see if it is leaking around your head. It can only be a few things. Yes, the reeds can drop the pressure but how much, I just don't remember. If one side is good, you should still test good on that side. Your reeds may need flipped over so they seat better. All in all, if you have a side with no visual problems, you need to look elsewhere. The first thing to do is check that squish clearance. Brandon Quote
David Keith Posted May 25, 2007 Report Posted May 25, 2007 Just in case you want to do a leak test yourself, here is all you need. Quote
. Posted May 26, 2007 Report Posted May 26, 2007 Just in case you want to do a leak test yourself, here is all you need. where do I get a paper towel with hearts on it, I have all the other parts, just cant find the towel :biggrin: Quote
Satsol67 Posted May 26, 2007 Report Posted May 26, 2007 Ring gap is within spec. (.30-.45mm) I filed and chamfered them myself. Head gasket has been re-done 3 times since I started this investigation. What else can it be. It ran great before I did some wiring and wouldn't restart afterwards. That's when I checked the compression. It had been leaking unfiltered air around the filter which took out the fresh rings. I honed and re-ringed her and still low compression. I'm stumped! If thats your ring gap that could be the problem. If I remember correctly ring gap should be something like .012 to .018mm but then again I have been known to be wrong. Quote
Olds Eddie Posted May 26, 2007 Author Report Posted May 26, 2007 (edited) Just in case you want to do a leak test yourself, here is all you need. If I interpret the parts correctly you plug up the spark plug holes, exhaust, and carb spigot on one side while putting compressed air to the other carp spigot with leakdown guage adaptor. Did you make your own spigot adaptor and plug? Edited May 26, 2007 by Olds Eddie Quote
Bansh-eman Posted May 26, 2007 Report Posted May 26, 2007 If I interpret the parts correctly you plug up the spark plug holes, exhaust, and carb spigot on one side while putting compressed air to the other carp spigot with leakdown guage adaptor. Did you make your own spigot adaptor and plug? to do a leak down, leave spark plugs in, remove your exhaust and plug them. remove carbs. plug them. one of the carb sides has the gauge one has the pump. you only want to build 6 lbs for a leak down test. and let it sit. if after 6 mins you still have 6lbs your good. click on RNBrad link in my sig he shows how to make a differant tester with a medical bulb. problem with using compressors is if you add too much pressure your going to blow your seals Quote
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