Excessive Engine Pressure
Road Master
Joined: Feb 2014
Posts: 913
Likes: 5
From: indiana
A shop that rebores engines has a procedure that they follow and they are quite aware of the importance of cleaning out the stuff that results from the machining process etc. In my opinion your cylinders are ok and your comp. test seems to prove this as your readings for both cyls. are equal and normal.
In my experience the psi. difference you see between hot/normal and hot/wet is ok. for a motor that has not been " correctly " run in yet.
You said you installed a aftermarket " breather ? " and i suggest you check that for proper operation. Also check the pushrod tubes to ensure you have replaced the old o/rings etc. etc.
I suspect that you have a simple oil leak at the pushrod tubes otherwise there would be oil spewing out everywhere.
Relax and let us know what you find .
In my experience the psi. difference you see between hot/normal and hot/wet is ok. for a motor that has not been " correctly " run in yet.
You said you installed a aftermarket " breather ? " and i suggest you check that for proper operation. Also check the pushrod tubes to ensure you have replaced the old o/rings etc. etc.
I suspect that you have a simple oil leak at the pushrod tubes otherwise there would be oil spewing out everywhere.
Relax and let us know what you find .
that's why I say this is a big problem. first time engine builders assume they are clean and find out the hard way they were not.
also a stock evo with a N grind cam and 12.9cc domes on the pistons will produce 185 to 190 ccp. but im guessing on his cam
so his compression is low. that's why I said to do a leakdown test to see how much is leaking past the rings.
Last edited by D_gyver; May 13, 2014 at 07:19 PM.
Thread Starter
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1st Gear
Joined: May 2014
Posts: 5
Likes: 0
From: Belleville il
I performed cylinders leak down test and discovered the following:
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
Likes: 5,448
From: la la land jerzey
I performed cylinders leak down test and discovered the following:
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
if the motor is not seated in yet like these numbers suggest and the loss in the timing plug hole is heard ( the pressure is passing the rings ) - you need to drive it a 1000 miles maybe and keep the RPMs under 3000 - some machine shops use a grit stone that takes longer than others
if you cant get the push rods to stop weaping you can use another top thick o ring in the center as that will make the tube very tight and it will seal it up -
drive it like a human for the time being --
Road Master
Joined: Feb 2014
Posts: 913
Likes: 5
From: indiana
I performed cylinders leak down test and discovered the following:
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Afterwards, test results of front cylinder at TDC is 25%. Rear cylinder at TDC is 22%. From what I understand, I newly rebuilt cylinder should be less than 20%?
Also, during testing of both cylinders, I could hears a slight hissing sound coming from the timing plug hole (plug was removed). Is this normal?
fxrstew
and I have 18% front 16% rear. and I have 2.6 cfm flowing out the breather.
after break in the cfm will drop to around 1.9
Road Master
Joined: Feb 2014
Posts: 913
Likes: 5
From: indiana
dont sweat the 2 or 3 percent difference - each directions i have read about doing a leakdown have never said anything about the compressors line pressure < and that will make a difference in the percentage loss overall
if the motor is not seated in yet like these numbers suggest and the loss in the timing plug hole is heard ( the pressure is passing the rings ) - you need to drive it a 1000 miles maybe and keep the RPMs under 3000 - some machine shops use a grit stone that takes longer than others
if you cant get the push rods to stop weaping you can use another top thick o ring in the center as that will make the tube very tight and it will seal it up -
drive it like a human for the time being --
if the motor is not seated in yet like these numbers suggest and the loss in the timing plug hole is heard ( the pressure is passing the rings ) - you need to drive it a 1000 miles maybe and keep the RPMs under 3000 - some machine shops use a grit stone that takes longer than others
if you cant get the push rods to stop weaping you can use another top thick o ring in the center as that will make the tube very tight and it will seal it up -
drive it like a human for the time being --
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
Likes: 5,448
From: la la land jerzey
but his discription was at the timing PLUG an audible sound coming from the plug hole
the Harley V Twin relies on a cylinder loss ( piston ring seal or lack of ) to be able to then use it ( high pressure air ) to lube the cam chest and all its workings Via the breather valve as it is timed to take advantage of the event -
jz
Stellar HDF Member
Joined: Aug 2013
Posts: 3,416
Likes: 3,502
From: Texas
I have built a bunch of inline 4s and that has been my experience with APE, you have to clean the cylinders yourself.
Club Member
Joined: Apr 2011
Posts: 5,764
Likes: 7,798
From: SE Louisiana
I performed cylinders leak down test and discovered the following:
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Front cylinder had strong airflow coming from the carb and rear cylinder had strong airflow coming from exhaust. I backed off the adjustment on all four adjustable push rods to ensure all valves were fully closed.
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
Likes: 5,448
From: la la land jerzey
i am just a guilty - not reading it to the end and end up answering something that is of no value - helping is sometimes a job - hahahhahaha