HarleyTechTalk

I had a cylinder base gasket leak. While I had the heads ,rocker boxes and cylinders off I painted them. Paint was coming off. I put it back together and ever since it is sucking the rocker gaskets in causing oil to leak. It is a 1989 fxst. It has plenty of air coming out of the breather hose. It runs great just leaking oil all over the place. Where it sucks the gaskets in is on the plug side on the lower rubber gasket at the ends of the rocker shafts. It doesn't matter how tight or loose the bolts are. Thought I was squishing them out till I watched it happen. They will stay in place till it idles about a half hour. You can watch it move in and then leak oil. 

OEM gaskets from HD?

Quote from: blueovalmechanic on August 27, 2023, 01:01:24 PMI had a cylinder base gasket leak. While I had the heads ,rocker boxes and cylinders off I painted them. Paint was coming off. I put it back together and ever since it is sucking the rocker gaskets in causing oil to leak. It is a 1989 fxst. It has plenty of air coming out of the breather hose. It runs great just leaking oil all over the place. Where it sucks the gaskets in is on the plug side on the lower rubber gasket at the ends of the rocker shafts. It doesn't matter how tight or loose the bolts are. Thought I was squishing them out till I watched it happen. They will stay in place till it idles about a half hour. You can watch it move in and then leak oil.

So how and when did the first leak occur? Just after some motor work? Or just out of the blue?

Some years (I think around 1990 ish) of Evo motors had some issues with the cylinder studs pulling from the case. I assume that when you torqued the heads/cylinders you could reach the specified torque? Maybe inspect each stud to see if any are higher than the others at the case.

What head gaskets are you using, OEM style or Cometic MLS gaskets? The torque spec is different for OEM style vs. MLS style.
As for the base gasket, OEM style or Cometic SLS style?

Have you checked the cylinder base for flatness, as well as the case where the base gasket mates to it?

Too much vacuum with a case breather? That's a new one on me, usually it's the opposite problem. And like Ohio asked, what was done to the motor? Any chance the breather gear is not timed correctly? (not that I know this could be cause) I made a crankcase pressure/vacuum adapter out of a timing plug that I drilled/tapped for a 1/8" NPT hose barb and hung a vacuum/pressure gauge on it. Case breather, at maybe 2000 rpm, has essentially zero pressure. A head breather has around 2" Hg of vacuum. Adding a Krank-vent to either gives about 3" Hg.

-JW

In 1989 a lot of big twins got defective rocker boxes, they were made from a substandard material, which made them too soft.

The parts would deform as the screws were tightened.

The older the parts got, the worse the problem got.

I bought a new set of OEM rocker boxes about 2 years ago for my `89 Softail because I couldn`t even snug the screws down any more without distorting the boxes.

The latest Rocker Box Gaskets are not rubber, they look like Teflon, and they work great.

Wait a minute. Everyone talking about gaskets, etc. Case vacuum is a harley engine builders dream. Heck, prostock sportsters run onboard vacuum pumps to create vacuum inside the case.

I seriously doubt the OPs diagnosis that case vacuum is causing the rocker boxes to leak. That dog won't hunt. Something else going on here. 

Take the rocker boxes back off. Get a piece of window glass at the hardware store. Put each part of the rocker boxes on the glass and use a feeler gauge to see if they are flat. If they are not flat, you need a new set.
If they are flat, get a new gasket set from Harley or Cyco. In my experience they work better than the other brands by far.

I began this with a base gasket leak on the front cylinder base gasket. I bought this bike not running. Cleaned the carburetor and replaced the oil pump. Oil pump replaced because the seat on the check ball was bad. The crank case was flooding instantly. I got it running good. I soon developed a cylinder base gasket leak on the front cylinder. I rode it a while this way but the mess got worse and that bothered me. I bought a gasket set off eBay. I pulled in apart. The paint was in bad shape so I painted the heads,cylinders,lower rocker boxes and upper rocker boxes.  leaving the middle section chrome. The studs all are the same length. My cylinder base gaskets and lower rocker box gaskets were the paper kind when I disassembled it. The rocker box gaskets were black rubber and not leaking on disassembly. When I painted what I did I taped it off to not have any paint on gasket surfaces. On a side note I have rebuilt a '94 ultra and a '94 sportster. I did very similar paint and used the metal base and lower rocker box gaskets. I used the same brand gaskets on this bike and the factory service manual and head torque procedures. This is the first bottom breather I have owned. I put the rocker boxes the same way I did on the two '94s and my '97 road king. I didn't have any leaks on those three. Back to the '89 softail. I torqued the heads and then assembled the rocker boxes. When I disassembled it it had black rubber gaskets. The new set were black rubber as well. They leaked. I went to my local independent and asked him for a good set. He said the black ones were junk and sometimes squish out. That was what I experienced. The squished out where the inner fence for the gasket isn't at. By the rocker shafts. He sold me a set of grey rubber ones saying they were better. Same result. When they squished in. Not out. I thought I did something wrong. I read the manual and as I noticed it read the same as my top breather instructions. I got another set of the rubber gaskets. I checked for flatness. The lower box where the problem is occurring was dead flat. The top box is dead flat. The middle section has a very slight upward bow in the area that the problem occurred. The problem is between the lower and middle section. When I assembled it this time I checked and fully assembled the gasket is in place and the bow is gone. It stayed overnight without moving. I was feeling good. I fired the bike up and it idles fine. After about 20 minutes the gasket started moving in at the same place. I assumed it was vacuum. It moves inward. I would think if it was pressure it would move outward like when I had a bad umbrella seal on a to breather. I ask those with more experience. I think I am doing it right but it isn't going right. I tried again thinking I was tightening the four top bolts too much. I put it together finger tight. I fired the bike up and had it leaking oil. Of course. I then slowly and evenly tightened the four bolts till the oil quit coming out. Wiped up the oil. It ran about 20 minutes again. I watched the gasket move in slowly till the oil was leaking again. I am at a loss of what to try next. Sorry for being so long winded but from my years as a ase master certified mechanic I know that information is usually the key to the failure. I tried to answer your questions and give all I know thinking that I am overlooking something. Thanks for any help 

Bought the gasket that I am having problems with from hd dealer. Genuine Harley Davidson. Will up date results after install 

Something I used to do with the old rubber and cork (remember them?!) Evo rocker box gaskets was this:

 Lay them out flat on a piece of waxed paper and spray them with 3M contact cement. Let it tack up and then press the gaskets into their respective channels. If this doesn't work for you, then maybe you need to go back and make sure that the breather gear is timed correctly.

headbreathers don't use the umbrellas.

Maybe cork gaskets is the solution? IIRC, the -89 lower box is missing the gasket guides that came later.

Quote from: Ironheadmike on September 06, 2023, 06:19:30 PMheadbreathers don't use the umbrellas.

Remember that early slabside engines used breather control valves that were timed to the crank rotation.  They've been around for a long time and don't relate to just head breathers.

As above used on evo as well but plastic crap

Quote from: Ironheadmike on September 06, 2023, 06:19:30 PMheadbreathers don't use the umbrellas.

Head breathers DO use umbrella valves.

Case breathers DO NOT use umbrella valves.