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Discussion Starter #1
new motor- two cylinder v twin- 30% front cylinder 8% rear compression 180 on both, bore scope looks good on both but blowing into the lower end on leakdown on front cylinder. any thoughts or just run it
 

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Hot? Cold? I you leak a motor cold and dry you can hear the rings flutter sometimes. When you leak it is the air going past the rings?
 

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Is the leak down the same if you move the piston/rotate the crank 10 to 20 degrees? If yes, then that's a thumbs down. If no, then run it.
 

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Discussion Starter #8
tried moving the crank 20 degrees both ways with the pushrods out, no difference so i'm going to run it, thanks for all the help
 

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Capri For Sale
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Imo it's leaking 30% through the bottom end no matter how you check it, it's broke.
 

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Motorboatin SOB
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I leak my shit at TDC and both valves backed off...if yours leaks 30% at TDC theres an issue IMO.
 

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Run it till it warms up, then run it FUCKIN HARD, THEN KEEP RUNNING IT HHHHAAARD!!! Then let her cool down. Then run it around at moderate power. Shut it off and recheck the leak down.
Rings WON'T seal unless it's put under load.

I run turbo engines until they are warm .........then put them in gear and slowly bring the rpm up against the converter until the boost gauge starts to move, then I SLAM THE THROTTLE OPEN UNTIL THE TIRES SPIN (POWER BRAKING IT). Then I hand the keys to the owner and tell him to drive it like he stole it. After 200 miles, change the oil/filter. (I had already done so before handing them the keys and I had cut the filter open and checked for debris-by the way). Let your V-Twin EAT!!!!! There is t anything (based on what you have posted) that will hurt your engine more..............Run it!
 

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Long Live The King
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tried moving the crank 20 degrees both ways with the pushrods out, no difference so i'm going to run it, thanks for all the help
If it's not blowing oil run it.
 

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How old is this motor? do you feel its broken in yet?


If you have some miles on it why did you do the leak down? is it running poorly?


Still wondering what type of V twin still? ..... I assume its a Harley? and if so is the breather Timing set right? (depending on what Harley as well!)


Every motor can be different! more info may give you better advice!
 

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Discussion Starter #14
v twin drag bike-45 degree aftermarket motor-no cooling fins-motor has been heat cycled three times-down the track once-not blowing oil into the breather tank-external oil tank with crankcase vent
 

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Think you need to pull the piston/rod from the offending cylinder and look at the piston, ring lands, rings and bore over really well.
 

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v twin drag bike-45 degree aftermarket motor-no cooling fins-motor has been heat cycled three times-down the track once-not blowing oil into the breather tank-external oil tank with crankcase vent
What aftermarket motor? ........... I had a Ultima 127 that had Prosody in one Ex port! ..... to make that better it was into the oil drain back hole and was burning oil as it leaked into the port!


That's not something you see a lot of! but is a good reason to take it down and have a look!


Seen a motor bolted up without a oil support ring once! that one ran great but smoked on start up only! .... never did a leak down not sure you would see that on a gage tho?


Do you race in the AMRA by chance??? I always make the US131 race!
 

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Think you need to pull the piston/rod from the offending cylinder and look at the piston, ring lands, rings and bore over really well.
This! ....................... Except you should not have any need to pull a rod .... that's not easy on a Harley!


Just need to pull the top end off! and be sure to pull the cylinders not just a head! ...... cant see rings with the head off!


New gaskets should be like $60 ..... and your time to do it! ....... Some gaskets I reuse if there good! MLS head gaskets that still look great I use again! ...... if this is a EVO or Twin Cam rocker box gaskets I always re use if not damaged! ..... and Twin cams have O rings for base gaskets unless its a huge bore!
 
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