[Aussiebloke]

I've got a 92 FXR which I fitted an aftermarket highflow airfilter kit to. The crankcase is now breathing through the heads. I blocked off the stock breather down near the oil pump. Since this I have noticed a slight oil seepage around the bottom of the barrels. Should I reinstall the stock breather ?

[ReeseSS]

You have more tubulence going on in the crank case now, and those gaskets at the bottom of the jugs are prone to leak anyway, so I would unplug the plug and relieve the pressure.
Side note: Blowby is inherient with Harleys, caused by the turbulence created by the downstroke of the piston interupting the oil trying to drain back to case. The S&S reed valve is the best fix I have seen, but there are others now.

[Aussiebloke]

Thanks Mate! Would it be best to drill a hole in the filter backing plate and reattach the stock breather, or just put one of those small breather filters on the pipe down where I've got it blocked now ? The only Blowby kit I've seen is on the Australian ebay site, I'll have to do a bit more homework.

[CD]

1993 was the first of the head breathers. Being HD, there were a few exceptions of course. Over the years, we have been asked if the "Cure" (CCP by Direct Parts product) would fit a pre-1993 model. 99% of the time they will not fit because the pre-1993 rocker boxes do not have the vent chambers cast into the rocker box lower and sandwich plates. Also, the backing plate bolts were not hollow as they are in the 1993 up models.

The few 1992 models that were head breathers had both crankcase and head breather setups. S&S engines used this setup for several years allowing a choice between head or crank venting or both.

Are your backing plate bolts hollow? That is the easiest way to tell if you have one of the few exceptions. Or, with the air cleaner cover and filter removed and the engine idling you should feel little puffs of air out of both the front and rear bolts.

I am not sure whether or not the international models held true to this time line though. I have come across instances of international models being returned to HD and retro-fitted to US specs and sold as current year models so, not 100% sure on that one.

What would happen if you plugged off the crank breather hole and you did not have one of the rare "dual" breathers? You would build up crankcase pressure and eventually develop leaks around gaskets. On the EVO's the weakest point in the gasket chain are the cylinder base gaskets. I have seen cam chest gaskets fail also but it is usually the base gaskets that blow.

if you do have a dual breather setup and did not already have leaking base gaskets, I doubt you have a blow by problem. Crankcase pressure can build up can be caused by a few things. Excessive blow by caused by poor ring seal, a burned (holed) piston, partially restricted crankcase breather or a plugged or restricted crankcase vent. If none of these conditions existed prior to the changes you made, it's doubtful any of these would be the cause of the blown base gaskets.

[ReeseSS]

Aussie, I would just add a filter to the pipe you blocked

[Aussiebloke]

Thanks for the info CD. I checked the heads prior to installing the high-flow kit by taking off the plug caps and winding the engine over to make sure they were breathable heads, this was all OK, the bolts are "banjo type", hollow so there were no airflow restrictions. The problem only started after I installed the kit and blocked off the bottom crankcase breather.

Thanks again ReeseSS. I think I'll try the filter fix first and see what happens.