Crankcase Venting for TC, Is it necessary?
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Tourer
Joined: Feb 2008
Posts: 403
Likes: 44
From: Montana
Crankcase Venting for TC, Is it necessary?
Hi all,
Quick question for those in the know. I have a 15 RGS stock 103 HO with stage 1 AC, V&H true duals and Rinehart's. Was dyno tuned for the stage 1 and runs well. 70k on her and other than a couple sets of lifters all good. I have installed the DK breather bypass and vent to the ground about 60k ago. I have read the M8 engine can benefit from venting the crankcase. I get very little blow by out the head bypass hose. Finally to my question, do I need to vent my crankcase?
Thanks........goldie
Quick question for those in the know. I have a 15 RGS stock 103 HO with stage 1 AC, V&H true duals and Rinehart's. Was dyno tuned for the stage 1 and runs well. 70k on her and other than a couple sets of lifters all good. I have installed the DK breather bypass and vent to the ground about 60k ago. I have read the M8 engine can benefit from venting the crankcase. I get very little blow by out the head bypass hose. Finally to my question, do I need to vent my crankcase?
Thanks........goldie
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
No need to vent the cases separately, no. It's all connected and all technically makes up the "crankcase".
But improving on the breather valves in the rocker assemblies/heads sure can't hurt. Especially on high hp performance builds. I've always felt the stock breather system was adequate at best and the location of them less than ideal.
On my Sporty I rendered them useless by using solid bolts in the heads when mounting my AC/backplate. I then drilled and tapped a hole in the front of my cam cover and threaded in a 1/8 NPT to hose barb 90° that I ran a 3/8 hose off to under the bike. Approximately 6" from where the hose connected to that 90° I cut it in half and installed the KVP38 Hayden Krankvent.
This worked much better for several reasons but main!y because it closed quicker(instantly) not allowing ANY air be sucked back in on upstroke which helped maintain a more constant, stable slight vacuum condition in the crankcase most importantly under the pistons allowing them to go up and down effortlessly and not fight against a positive pressure of any kind.
It also had a cleaner look being practically hidden and no unsightly hoses dangling off the heads.
The krankvent also split in two making it easy to clean or replace the actual valve should it ever be necessary WITHOUT taking the bike half apart to get to and was not affected by the high heat associated with being in the heads.
The engine working more effortlessly was noticeable at first start and made for a freer revving engine.
Pesky oil leaks are also a thing of the past when maintaining a slight vacuum.
I haven't figured out the best way to vent the twin cam crank case yet and so far the stock setup has been adequate enough as in not causing any major issues but I know it's not ideal either except to make it easier to vent to the intake which we all undo anyway for obvious reasons.. That may change with my on going build.
Venting from the cam chest...
But improving on the breather valves in the rocker assemblies/heads sure can't hurt. Especially on high hp performance builds. I've always felt the stock breather system was adequate at best and the location of them less than ideal.
On my Sporty I rendered them useless by using solid bolts in the heads when mounting my AC/backplate. I then drilled and tapped a hole in the front of my cam cover and threaded in a 1/8 NPT to hose barb 90° that I ran a 3/8 hose off to under the bike. Approximately 6" from where the hose connected to that 90° I cut it in half and installed the KVP38 Hayden Krankvent.
This worked much better for several reasons but main!y because it closed quicker(instantly) not allowing ANY air be sucked back in on upstroke which helped maintain a more constant, stable slight vacuum condition in the crankcase most importantly under the pistons allowing them to go up and down effortlessly and not fight against a positive pressure of any kind.
It also had a cleaner look being practically hidden and no unsightly hoses dangling off the heads.
The krankvent also split in two making it easy to clean or replace the actual valve should it ever be necessary WITHOUT taking the bike half apart to get to and was not affected by the high heat associated with being in the heads.
The engine working more effortlessly was noticeable at first start and made for a freer revving engine.
Pesky oil leaks are also a thing of the past when maintaining a slight vacuum.
I haven't figured out the best way to vent the twin cam crank case yet and so far the stock setup has been adequate enough as in not causing any major issues but I know it's not ideal either except to make it easier to vent to the intake which we all undo anyway for obvious reasons.. That may change with my on going build.
Venting from the cam chest...
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
hummmm????
well, when you start getting more blow-by or going positive on upper rpm, you will vent oil out that vent. the hd head system uses a coalescer to separate the oil from the gas. the ole irons used a centrifugal system in the cam case to do the job. (remember oil pooling)
stock system works well if you put the vent into a high flow area, the issue is lazy flow and particulate drop out, all about keeping the style.
well, when you start getting more blow-by or going positive on upper rpm, you will vent oil out that vent. the hd head system uses a coalescer to separate the oil from the gas. the ole irons used a centrifugal system in the cam case to do the job. (remember oil pooling)
stock system works well if you put the vent into a high flow area, the issue is lazy flow and particulate drop out, all about keeping the style.
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
hummmm????
well, when you start getting more blow-by or going positive on upper rpm, you will vent oil out that vent. the hd head system uses a coalescer to separate the oil from the gas. the ole irons used a centrifugal system in the cam case to do the job. (remember oil pooling)
stock system works well if you put the vent into a high flow area, the issue is lazy flow and particulate drop out, all about keeping the style.
well, when you start getting more blow-by or going positive on upper rpm, you will vent oil out that vent. the hd head system uses a coalescer to separate the oil from the gas. the ole irons used a centrifugal system in the cam case to do the job. (remember oil pooling)
stock system works well if you put the vent into a high flow area, the issue is lazy flow and particulate drop out, all about keeping the style.
But it's also in an area where oil splash is non existent in the first place.This design was used by many in the Sportster community and proved to work very well and way better than the stock system. Especially in performance builds where the stock proved insufficient.
Last edited by 60Gunner; Jan 21, 2022 at 08:22 AM.
Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
It can hurt. Depends how it is done and the reason for it.
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Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
yes, i have seen that mod before, BUT
do you think the oil is mostly fluid or better yet a liquid in the cam case?? hummm??? with all of the gearing in the case, it would be more on the aerated than not, ever look at the return flow?
your engine will turn to a positive pressure above 5k, when this happens, less diff'l so oil does not move that well therefore it pools, mostly in the flywheel compartment and when the engine returns to a negative, the oil will flood into the cam case, so the case will be over-whelmed. on the stock setup, the vent must travel upward so gravity helps drop out and then the mazes takes over.
even the ole irons would puke oil out the down tube when excess oil was in the case.
for a stock and a well fitted engine with little blow-by not much issues, but time marches on and nothing lasts forever so you will start getting oil out the case vent. trust me, the moco would have put the vent there if they thought it to be white on rice.
all of this hoo-doo is nothing but band-aides, when mine starts huffing oil out the cleaner with my mod, it is time to open the wallet or trade her in. hd needs to look seriously at rice.
but then again people like to be separated from their money, hummm!! i got a bridge to sell, located in brooklyn. you know two bars of green lava soap in a wool sock inside the cleaner is worth 15 more hp, the black bar only 10 but it cleans the carbon out!?!
do you think the oil is mostly fluid or better yet a liquid in the cam case?? hummm??? with all of the gearing in the case, it would be more on the aerated than not, ever look at the return flow?
your engine will turn to a positive pressure above 5k, when this happens, less diff'l so oil does not move that well therefore it pools, mostly in the flywheel compartment and when the engine returns to a negative, the oil will flood into the cam case, so the case will be over-whelmed. on the stock setup, the vent must travel upward so gravity helps drop out and then the mazes takes over.
even the ole irons would puke oil out the down tube when excess oil was in the case.
for a stock and a well fitted engine with little blow-by not much issues, but time marches on and nothing lasts forever so you will start getting oil out the case vent. trust me, the moco would have put the vent there if they thought it to be white on rice.
all of this hoo-doo is nothing but band-aides, when mine starts huffing oil out the cleaner with my mod, it is time to open the wallet or trade her in. hd needs to look seriously at rice.
but then again people like to be separated from their money, hummm!! i got a bridge to sell, located in brooklyn. you know two bars of green lava soap in a wool sock inside the cleaner is worth 15 more hp, the black bar only 10 but it cleans the carbon out!?!
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Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
Yeah it travels up...up the same tubes oil drains down. Dumb.
I know you're also aware of all the people running this mod quite successfully, right?
The moco USE TO vent in the cam chest til all the EPA bs and routing to the intake if you recall. For a couple years it was still vented there and routed UP to the air cleaner. Venting closest to the source is still best.
If the moco knows and does best then explain to me why it's vented to the intake. And don't even say it doesn't cause damage because it does. The carbon build up can and will lead to serious issues with detonation not to mention the heat.
My Jag runs between 10 to 16inHg of vacuum at all times. I use a dual clean side port catch can. One hooked to the stock line running to the intake. The other to an electric vacuum pump that kicks on when vacuum drops below 10inHg at the intake under load. It kicks off at 16 inHg. I get very little oil in the catch can. A pesky oil leak at one of the variable valve solenoids ceased leaking immediately. Hasn't leaked since.
I know you're also aware of all the people running this mod quite successfully, right?
The moco USE TO vent in the cam chest til all the EPA bs and routing to the intake if you recall. For a couple years it was still vented there and routed UP to the air cleaner. Venting closest to the source is still best.
If the moco knows and does best then explain to me why it's vented to the intake. And don't even say it doesn't cause damage because it does. The carbon build up can and will lead to serious issues with detonation not to mention the heat.
My Jag runs between 10 to 16inHg of vacuum at all times. I use a dual clean side port catch can. One hooked to the stock line running to the intake. The other to an electric vacuum pump that kicks on when vacuum drops below 10inHg at the intake under load. It kicks off at 16 inHg. I get very little oil in the catch can. A pesky oil leak at one of the variable valve solenoids ceased leaking immediately. Hasn't leaked since.
Last edited by 60Gunner; Jan 21, 2022 at 04:20 PM.
Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
Oil doesn't drain down pushrod tubes. Most oil drains down by exhaust valve though cylinder into cam chest on TC and m8's and evo's to crank cavity.
No doubt the EPA has had some effects for the way Harley routes it's breathers, but changing that to external breather compared to if it needs more vent holes is not the same topic.
No doubt the EPA has had some effects for the way Harley routes it's breathers, but changing that to external breather compared to if it needs more vent holes is not the same topic.
