Watch that breather vent!

[Darrell]

I was late for a breakfast meeting and ran my 250SL at 65-70mph for a few miles to make up the time.

During breakfast the crankcase leaked out about 3/4 cup of oil. At first glance it appeared to be a catastrophic O-ring failure on the kickstart shaft. Upon a closer look oil was weeping from about every seal and seam.

You might be able to guess the problem and solution now. I picked at the breather vent with a piece of wire then blew it through with compressed air until it exhausted through the filler hole with only as much resistance as you would expect.

It's all good and leak-free now. And a huge relief too...I had visions of a case-splitting procedure to get to that kickstart O-ring! Hope this helps someone someday.

[Charlie R]

Darrell, I'm glad the fix was a simple one. That scenario could cause one to pucker. If I may share a tip that someone here might be able to use regarding crankcase venting- I remove the standard vent fitting and drill it from the bottom all the way through the top. After re-installing the vent, take a short length of 1/4" vacuum hose and slide it over the vent and route the hose to the backside of the engine. I safety wire the hose to the vent but its not really necessary. Vents great and water and dirt stays out.

[Zyx]

I did something different back in my race days. I found that the oil dip stick threads were same as a spark plug. So I knocked the guts out of an old plug and brazed a short length of tube, maybe 3/8 diameter, whatever fit, and an inch or so long. Replaced the dip stick with the vented spark plug thingy, and attached heater hose with a clamp, and ran the hose up under the seat. I went through some very deep water during hare and hound racing in Kentucky and never got water in the cases, and that large hose breathes extremely well. These days I would also put a small breather filter on it just to be sure but I ran without one for two years of racing without issues. If anyone is interested I still have it and can post a photo.

[hodakamax]

Here's my input. Harry Taylor thought that this was needed to cool the transmission. The breather fitting was drilled out and a hose installed, as was on the oil check access. A filter was installed on the end of the hoses. Think about it. The transmission under stress had no way to vent the heat. Anyway, it was done on the short tracker early on. Seemed like the way to go.

Maxie

[Charlie R]

Wow Maxie! I was looking at your bike (Nice!) and remember the old peanut tanks from back in the day. I still have one of those mounted on an old roller. Not near that nice tho...

[Zyx]

Maxie,

The side case vent you show is what I used to use ( made for different material), except yours is better looking. Same idea though. On the question of venting heat, I would posit that if it vents air it also vents heat, but the venting of air is limited to volume differential between cold and hot. That is, not much, therefore not much heat either.

This is like venting the differential housing on a race car that sees water dunking from time to time as mine does. Plunged into cold water, a hot case or differential will be cold shocked, and while this rarely or never gets to a change in temperature of the gears, it does rapidly change atmospheric pressure inside the housing. That rapid change can't be handled my a microscopic vent hole, and you end up pulling water into the case through the same points that will leak oil under pressure if the case is not vented adequately. I suppose there is a way of determining the volumetric change of air at standard altitudes across the working temperature range of a Hodaka, but the amount of air is minimal, like half a pint or less. Without a forced airflow, cooling is not the reason for the vent, apologies to Harry. Transference of water, oil, and contaminants is the reason for the vent. The idea is to not create either pressure rise or pressure inversion inside the case no matter what happens outside the case. Street bikes that heat and cool gradually are served well enough by the case vent provided, as long as they are clean. Those subjected to extremes of temperature over short periods need additional vent capacity to stabilize atmosphere inside the case.

I would also suggest that if you are going to use a side cover vent of the type shown, the original vent becomes more of a liability than a benefit, and I would delete it. That tiny vent sitting down in the case cavity is the most likely point things can leak in, even if there is a hose on it, and the additional passage of air through such a small hole if there is any, compared to the relatively enormous hole provided by the side vent, is not worth either the effort to make it better, or the risk of failure during an event, especially off-road because that point on the cases holds water and dirt.

I like the clear hose on the vent. Just could not afford such extravagances when I was young.

[hodakamax]

Another use for all these hoses was simply to mystify and worry all your competition. In reality, probably all they provided was an exit for condensates and heating and cooling pressure changes but they did look cool! We called it "Other secret stuff".
I think I'm giving out classified information---later,

Maxie

PS--I do remember an instance with a lubricant we tried that foamed and would spit out the standard vent at high RPMs. The big hose stored the foam and recovered the lubricant rather than blowing it out on the engine.

[Zyx]

Yep. There is always a bit of oil vapor mixed in with the case air, and it will pump out, especially through th standard vent. Oil splash hits the top of the case inside where the vent is, and changes in pressure carry some of that condensed or splashed oil or oil fog out through the vent. It also drags it back in when it cools, which is not so good. Which is why I would rather just delete the little vent in favor of the big one. You will see some oil in the breather line as you would with any crank vent system. The new Ford Mustang GT has an oil recovery system because of significant oil pumping through the case vent, and you have to empty the recovery jar frequently. My Cummins diesel has a recovery vessel on the front of the block that has to be emptied periodically for the same reason.

So it is with the Hodaka cases particularly when raced. As long as there is a filter on the high end of the tube to keep crap out of the line, that vent does a great job of venting and recovering oil vapor, and keeping case pressure static at all temperatures.

I read that automotive tires gain one psi pressure for every ten degrees Fahrenheit rise in temperature. Hot air has a larger volume than the same air when cool. The engine case would do the same, which is why the OP had an oil leak. If the case temperature went up, say from 70 degrees to 170 degrees, there would be a rise of 100 degrees, which should be good for 10psi. That's a whole bunch of pressure inside an engine case. As long as the vent is free of debris, that pressure rises and falls over several minutes, and the vent can handle it. But for racing, the vent is marginal at best, which is why the side case vent is important. In a short moto, maybe it is no big deal, but cross country or desert long distance, or anywhere you have to cross water, it is a big deal.

But I really like the looks of the clear vent line. Gonna have to get some.

[taber hodaka]

The only time I had an oil leaking problem, was when I must have used an oil that foamed, I did use automatic transmission fluid as recommended by Hodaka. Cross country and motocross about 50 / 50. The old ace 90 has been submerged in water before.=========Clarence

[Zyx]

For the record, the spark plug that fits the dip stick hole is not the plug from a Hodaka, but from a 300cid Ford six. It is an eighteen millimeter plug with a tapered seat. Fits right in and seals without a gasket.

Spark plug bodies are oriented threads upward

Plug on the left is an 18mm plug. For comparison, the one on the right of made from a B8EV from a Hodaka. One is my old vent adapter, the other is used for mounting a dial gauge to set ignition timing.

[hodakamax]

Ford stuff on a Hodaka? Is that legal?

[Zyx]

Super Secret Mods.

[hodakamax]

Hey Gang, I went to the hardware store last week and found some fittings that work good converting the oil filler hole to a breather vent. It is a 1/2 inch Barb x 3/8 inch MIP fitting. Slightly loose but the right number of threads per inch. Comes in plastic, brass and probably anodized aluminum. A little Teflon tape to protect and seal the threads and you are set! Just a follow up to our discussion.

Maxie

[Zyx]

How curious that threads on pipe fittings are compatible with metric. I will have to go out to the garage and compare die sets.

[hodakamax]

AZ, give us a report. My sets don't go that big. Even the brass one tightens down in that distance without interference but is slightly loose in the bore. With a little Teflon tape it fits nicely. I also slipped an O-ring over it to provide a softer bottom out.

Maxie

[Zyx]

Preliminary comparison between 18mm versus 3/8 NPT is they don't match, and probably work here only because the threads are loose and allow for the mismatch. Question is, will the NPT fitting stay in place during riding, or pop out. I will do a closer comparison shortly.

[hodakamax]

Close enough for Government work! --I did tighten the plastic one really snug and it did seem to be secure. Did you finally find some clear hose for your project? By the way, 5/16" ID works perfect on the stock breather vent after drilling it out with a 1/8" drill. The 1/2" on the filler hole is probably overkill but it does look cool!

Later

Maxie

PS---this does work great, but brings up the question about a metric version in anodized aluminum that would be cool! Someone check it out in their spare time!

[Zyx]

Here is a side by side comparison of an 18mm thread chaser and a 3/8NPT tap. (NPT is National Pipe Thread - MIP is Male Iron Pipe, same thing). 18mm is 18x1.5, 3/8NPT is 18 per inch tapered, which converts to 1.41mm pitch. The photo shows 1.3 approx. 1.41 is deduced mathematically.

I measured minimum and maximum diameters at the broadest part of the NPT tap. The rest of the thread length is smaller due to taper of around 1:16. Bottom line is that while the Teflon will take up the slack in diameter, only a partial rotation of thread will be in contact between the two. It might bump out of place if knocked with your foot.

Posted twice, you guys tell me which views right side up

[Zyx]

image.jpg (42.31 KiB) Viewed 6251 times

Available on EBay for ten bucks. 18mmx1.5mm to half inch barb, black anodized aluminum.

[Zyx]

Ordered one out of Walnut, CA for 8.99 w/free shipping. Will report on arrival.

[hodakamax]

Mine has been in place for 45 years---haven't kicked it out yet. But cool on the metric one, thanks for the look-up, give us a pix and make sure you use non-opaque hose!

Maxie

PS--the very first one I used on the short-tracker in about 1967 was a blue anodized, probably 3/8" fitting with a 30 degree bend on the barb. I found it in my dads junk and I have no idea where it came from.

[hodakamax]

A bit of history--This was not Max's idea but Harry Taylor's to improve venting on competition engines. Dealers of the day received bulletins on modifying Hodakas for competition. In the bulletin on "Modifying the Ace 100 for Road Racing" Harry described how to vent the crankcase with, yes, pipe threaded fittings into the oil filler hole. It never seemed to "pop out" even at speeds exceeding 100MPH. All of our race engines were modified in this manner even though it was probably overkill. Drilling out the standard breather with a 1/8" bit and installing a hose probably met the requirements of all but the road race and other sustained high RPM racing.

Maxie

PS--Now I'm off to more important things like the Tiddleywink competition today!

[hodakamax]

Now that we have established that the 1/2" barb x 3/8"MIP fitting meets and exceeds requirements for a low volume vent let's move on to the other end of the hose. Here's a picture of filter installed on the 5/16" ID hose. It's been so long ago that I've forgotten where it came from. We now need a 1/2" barb to filter to complete our venting kit. The old short tracker just had a cotton glove finger safety wired on the hose. A quick search revealed some other options. This would be a better looking option!

Later

Maxie

[Zyx]

There are so many breather filters out there for bikes and cars that getting one you can use should be simple. I have gotten mine at AutoZone. Mine just pushes into the tube and is held with a hose clamp. No barb fitting required at the filter end, but I don't use plain paper style, only foam or oil able gauze due to occasional water.