Crankcase ventilation

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snookwheel
Posts: 152
Joined: January 28th, 2008, 8:32 pm

Crankcase ventilation

Post by snookwheel »

I have found that after several successive runs, getting up next to the 7,100 rev. limit results in some white smoke and some oil venting into my vented catch can. Actually, a fair bit of oil. 8 0z. after the last test and tune (12-15 runs).

The only crankcase vent line I have runs from the oil fill tube to the catch can. It only seems to happen (smoke & oil venting) after the engine is hot and I am hitting the top of my rpm range. Would adding vent lines to my valve covers help? Or, is this simply the world of high performance VW engines? The engine has a fresh rebuild (4 hours) with Total Seal piston rings.
Lynn
Posts: 592
Joined: June 24th, 2006, 11:15 pm

Re: Crankcase ventilation

Post by Lynn »

When I picked up my engine from the builder after its conversion to a 1914, he said the valve covers should be vented.
69 Beach Solo Vee, #65 FM

85 Lynx B Solo Vee

71 Zink C4 Solo Vee
snookwheel
Posts: 152
Joined: January 28th, 2008, 8:32 pm

Re: Crankcase ventilation

Post by snookwheel »

I took the advice Lynn. 1/2 inch ID lines off each valve cover to a home-fab catch can. Hope my wife does not go looking for the container of pesticide... it just fit too well not to use!
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Crankcase ventilation

Post by brian »

Make sure you have some expansion area below your vent hose. The stock generator housing has an open area to absorb much of the pulsing inherent in our motors. If your filler housing is too small, this pulsing will venture into the vent line, and if it's too small or crimped, backpressure will increase and oil will migrate into the catch tank. I recommend using the factory aluminum baffle as well. Make sure your hose is not crimped and travels up above the connection before going to the catch tank. This will help in de-oiling the air.

Last, but certainly not least, is leakdown from the motor. If you are seeing smoke, there's excessive blowby from the rings. Leakdown tests with our ring packs tend to be misleading when it comes to determining ring seating. I would do a clean shut off and read the sparkplugs. If they are black and wet, it's time to look at your rings.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
snookwheel
Posts: 152
Joined: January 28th, 2008, 8:32 pm

Re: Crankcase ventilation

Post by snookwheel »

Thanks for the information Brian. The container I used has a 16oz capacity. I drilled a 1/2 inch breather hole in the screw top, with some steel wool like material in the hole to hopefully prevent any potential for oil spraying. It is mounted almost as high as my air filter

I did pull the plugs and they were dry and light brown. However, that was after a brief period of sitting at idle in the garage. I will pull them after a hard run and clean shut-down next weekend to see how they look.

Here is a clip of a run which shows the smoke. This was after several runs, and the engine was hot. In the first stretch, I stayed in 2nd and was right near the 7K red-line. I shifted to third on the return, and there was no smoke. In later runs, I shifted to third in the front slalom, and there was not a smoke issue. (still figuring out how to drive and when to shift this.)
Does this look to be evidence of potential weak rings?

http://www.youtube.com/watch?v=GgXKSpM_Jjk

Third has plenty of torque, so I probably don't need to be banging against the red-line. I'll learn.

Scott
ultimate42
Posts: 30
Joined: June 25th, 2006, 7:33 pm

Re: Crankcase ventilation

Post by ultimate42 »

The problem occurs when you lift off of the throttle when still in gear. These motors are tight enough to create a vacuum in the crankcase at that time. You will also notice that you will suck in your valve cover gaskets too! The best thing to stop this is to ventilate the valve covers. Bugpack has a kit for this, available at your local buggy shop. The smoke you saw was probably leaked from your gaskets, and onto your exhaust.
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: Crankcase ventilation

Post by SR Racing »

The FV engine has no valve guide seals and many have pretty sloppy guides in them. If it smokes on a downshift, it is usually due to oil being sucked down the valve guides in to the cyclinders and being burnt. So it does come out the exhaust. Excessive oil levels, no oil restrictors in the push rod tubes, or very worn guides are usually the cause. Keep in mind that most all will smoke a little after lifting the throttle and downshifting. Of course, rings or poor cylinder wall patterns will contribute to smoking also.

Jim
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: Crankcase ventilation

Post by SR Racing »

After looking at the video, it looks like the issue is not one of sucking oil into the guides. It appears to happen as soon as you get on the throttle after a higher G turn. Oil in the case splashes into the lower cylinder bores and then burns. So ineffective windage, or rings are probably the problem. (or excessive oil levels)

Jim
snookwheel
Posts: 152
Joined: January 28th, 2008, 8:32 pm

Re: Crankcase ventilation

Post by snookwheel »

Thanks Jim. What does windage refer to? That is a new term for me. As far as oil capacity, I am using four quarts of oil. I am running an external oil filter.

Scott
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: Crankcase ventilation

Post by SR Racing »

There are normally trays (aftermarket or custom built) that fit into the engine case that seperate the oil from the crank, cylinders and pushrod tube holes. They tend to decrease the amount of oil that flops all around the VW engine case. This oil actually gets up to the crank journals causing some loss of HP. The crank now has to turn through this mist. ("Windage")

The original VW never saw turns over .6 G's and you are probably double that. So without a windage tray (and to some degree with it) the oil will fill the lower cylinders, push rod tubes, etc. In theory the oil rings should wipe this oil down on the downward stroke. However, with lots of oil on the walls during the intake cycle more will get sucked into the combustion chamber than should. So smoke. Unless you are fouling a plug, it don't hurt much, but most people and mosquitos don't like it. :lol:

The VW does lend itself to lots of blow-by. The aluminum head, silly cylinders and case take on all sorts of shapes as the temperature changes. So ring seal will never be as great as a modern engine. The more you vent it the better. Be carefull venting valve covers though. While it limts case blow-by, IF your valve area of the head gets lots of oil in it, the pressures will simply blow the oil out of your vents and fill your catch can. That is why restrictors are used to prevent the oil from flowing out the push rod tubes to the upper head in turns. Making sure the vents are as high as possible on the valve cover and the hoses run "uphill" to your catch tank will help.

Keep in mind this diagnosis is from a U-Tube video and that most assistance is worth just about what you pay for it. So, I could be wrong. :lol:

Jim
jpetillo
Posts: 759
Joined: August 26th, 2006, 2:54 pm

Re: Crankcase ventilation

Post by jpetillo »

The smoke seemed to coincide with the right-hand turns heading away from the camera. Were those corners longer than the ones on the way back up the course?
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: Crankcase ventilation

Post by billinstuart »

If you're using dykes rings that seal with combustion pressure, closing the throttle collapses the rings and creates a higher pressure in the crankcase than in the cylinder, sucking oil up past the rings. ALL engines will puff a little smoke when the throttle is closed. Vee engines have thick rings that just don't seal well at high rpms anyhow. Since the second ring is basically an oil scraper, we've tried running without a second ring. Really good power, but unacceptable oil control. We also turned a used dykes upside down on the second ring to address the above condition. If it smokes in a turn, high rpm blowby can cause high crankcase pressure which forces oil out everywhere as it builds up on the side of the crankcase.
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: Crankcase ventilation

Post by hardingfv32-1 »

With a good ring system you should be able to get the blow-by down to 2-3 CFM. This is well within the design limits of the stock breather system. Having to vent the valve covers is an indication of a completely inadequate ring package.

For oil control on the cylinder walls, how about individual cylinder baffles to control the oil coming of the rod bearings?

How about a windage tray above the camshaft to control the oil coming off the cam?

Regardless of what package you use, you will always reduce the oil ring tension (drag) to a point that provides you a little smoke and uses about 1/4 qt of oil per 30 min.

Brian
SR Racing
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Joined: June 24th, 2006, 1:58 pm

Re: Crankcase ventilation

Post by SR Racing »

hardingfv32-1 wrote:With a good ring system you should be able to get the blow-by down to 2-3 CFM.
Typical blowby on a FV 1200 varies from about .7 CFM to 1.8 CFM on the engine dyno. I think 3 is a bit high..

Jim
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: Crankcase ventilation

Post by hardingfv32-1 »

What type of gage and what scale are you using?

Brian
ultimate42
Posts: 30
Joined: June 25th, 2006, 7:33 pm

Re: Crankcase ventilation

Post by ultimate42 »

I think what you are missing out on is that this is a SOLO vee, with a 1600 in it. The principal may be the same, but the 1600 has magnified the oil problem. Also, with the 8" and 10" wide tires on it, gee forces are a lot high than with the road-race vee 4.5" tires. I have used the valve cover ventilation for many years, and this is a quick, easy, and cheap fix to this issue. We do not spend 5000-7500 on our motors to get them "picture perfect", and neccessarily expect some issues, such as this one.
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: Crankcase ventilation

Post by hardingfv32-1 »

What you are missing out on is the extra HP that a good ring package provides. The extra 400cc are of no significance. Your oil problems stem from a poorly prepared engine. Doesn't cost any extra to do it right.

It is very unlikely you are pulling more G's than a road racing Vee. You can not be getting much heat in your tires even if they are an ultra soft compound. You also do not spend much time in any one corner to cause an oil pickup problem.

Brian
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: Crankcase ventilation

Post by SR Racing »

hardingfv32-1 wrote:What type of gage and what scale are you using?
We are using a J-Tec. On the Vee (and FST) we use a J-Tec VF563 (0.14 to 5 cfm). "Scale"? Not sure of what you mean by Scale. We use the calibration factors (0-5V) from the vendor. We have also used it on Frequecy and get the same measurements.

BTW, this measurement is taken from the oil filler vent, with any other vents plugged and most engines have a sand seal pulley.

So if anything it is on the high side of a typical VEE.

A general rule of thumb:

"Dividing an engines maximum horsepower output by 50 will give you a ballpark number for how much blowby you would normally expect to see. For example, a street performance engine that makes around 500 horsepower will typically have about 10 cfm of blowby with conventional pistons rings and ring end gap tolerances. Higher performance engines that are built to tighter tolerances will usually have less blowby, as might those with gapless piston rings. An 800 to 900 horsepower NASCAR motor, for example, might only have 5 cfm of blowby."

So 1 cfm is in the ball park and 3 is quite high.

The SCCA and NASA V8's that we build are not to much more than 3.
snookwheel
Posts: 152
Joined: January 28th, 2008, 8:32 pm

Re: Crankcase ventilation

Post by snookwheel »

Venting the valve covers seemed to do the trick! I ran an autocross yesterday and had zero repeat of the smoke issue and there was only a trace of oil in my catch can at the end of the day. I had noticed previous to venting the covers, that there seemed to be oil drips from the dip stick after running hard. As if it was being forced out the top. That seems to have cleared up as well. Many thanks for the advice folks.

A smoke free run!
http://www.youtube.com/user/snookwheel

Pic. of vent line.

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