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Discussion Starter #1
I just built my FLHTC from the frame up. My first build. Put a late model Evo in her and its blowing oil out of the rear base gasket. As much oil as I put in, she pisses out.. I dunno what the check is going on. Not experience in Harleys at all. I need help..
Thanks!
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Just Ride
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If it's blowing out the rear base gasket, that is the first place I'd look. What year Evo? Is it a head breather or case? If head then where is it vented? Couldn't see what air cleaner is on bike. Evo's like to be warmed up before riding. Been known to eat base gaskets without proper warming. No blipping the throttle cold. Main cause of gasket leaks.
 

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Discussion Starter #3
If it's blowing out the rear base gasket, that is the first place I'd look. What year Evo? Is it a head breather or case? If head then where is it vented? Couldn't see what air cleaner is on bike. Evo's like to be warmed up before riding. Been known to eat base gaskets without proper warming. No blipping the throttle cold. Main cause of gasket leaks.
I believe its a 95, top breather.
 

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its got a fresh top end. When we first started the bike it didn't leak. I changed the air cleaner and now it won't keep oil in her. I guess ill try to remove that and see what happens. The guy that built the motor is no longer on the project and I just don't have the knowledge to fix her myself. I about to sell it. Although it would make me sad, I can't do it alone..
 

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Just Ride
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Gotta make sure you have the proper bolts in air cleaner so it breathes right.
 

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Retired citizen
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Make sure that AC isn't blocking off the head breathers.
Still, if the rear base gasket is leaking it's a good bet it's blown out and needs to be replaced.
 

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91 FXLR
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Their advice that's been given you, you should address those concerns first.

Now, if everything checks out then you need new Cometic Base Gaskets.

Also EVO's are bad about the Rear Cylinders rear left side leaking Oil. Harley supposely finally came up with a gasket to fix it. Me I had lots of issues with my 2 bikes, it got to the point a New set of Base Gaskets lasted 3,000 miles before it started pouring oil out, that's nothing in Mileage.

So, I read in 2013 a EVO Base Gasket reply from a guy on this forum from Arizona! He said, He use the Cometic Base Gaskets in rebuilds and never had a problem with any leaks ever again, even on the hottest of days in Arziona. But he also added, He coats both sides of the Cometic Base Gasket with Permatex Avation Form a Gasket Sealant Liquid, Remember a Little Goes a Long Way he said. That Permetax is the Key to stop the leaking, it seals, never gets Dryied out or Hard and it's made for Air Plane Engines that go from extreme Heat to extreme Cold.

I thank that Man from the bottom of my heart for this information. My Base Gaskets have never leaked again, it was dirt Cheap. Plus I took them both on long 10,000 mile Vacation rides out West during August the hottest month. Not even a Stain of oil on that rear Cylinder left side from Oil.

Before that I talked to Harley Corporate and a Dealer! They had no idea how to fix it but would sell me a set of New Cylinders which I did once but it didn't stop it from leaking. That money was wasted.
 

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I think I posted about the EVO base gaskets a long time ago but here it is again.

Using the current OEM base gaskets cut a narrow slit (1/32") outwards from each cylinder stud hole. The slit relieves pressure build up in the stud hole due to temp fluctuations during engine heat up.

This info was harvested from a Custom Chopper article that a cycle shop had investigated the EVO base gasket problems. That shop installed sensors in the cylinders to measure temp and pressure differentials to find out what caused the base gaskets to fail.

The slits in the gaskets relieves the pressure that builds up in the cylinder stud holes ! Made sense to me so I've been slitting stock EVO base gaskets ever since.
 
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As already said, make sure the correct bolts are in the heads for mounting the air cleaner backing plate, it sounds like maybe this engine has a blocked breather.

When the cylinders come off, take them to a reputable harley machinist and have the bases of the cylinders trued on a lathe, that will do more toward eliminating base gasket leaks than any other trick.
 
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