The Hodaka Club Forum

When leakdown testing my Dirt Squirt, I noticed when I put soapy water everywhere that tiny bubbles were leaking out of a small hole on top of the crankcase just behind the cylinder where it meets the base gasket. At first I thought the base gasket was leaking but it's not. This is almost directly under the intake manifold. Is that hole a vent of some sort or what? By the way, it leaked down about 1 psi every 3 or 4 minutes.

No that is not a vent and it should not leak. But with a leak down rate of 1psi in 3 minutes, it isn't anything requiring immediate repair. Photo? In the mean time I'll try find the hole you are talking about on one of the scoots here at Hodaka Days.
Ed

PS: You aren't talking about the transmission vent are you?

No, it's a tiny hole on the crankcase landing where the base gasket and jug sit. It is on that landing just about under the intake and just barely behind the base gasket. It is a hole right between the two case halves. If you look at the last picture on this ebay ad you can see what I am talking about. http://www.ebay.com/itm/1977-Hodaka-DS8 ... Ciid%253A1

That "hole" represents a feature of the engine's porting. Are you using a DS 80 jug and gasket? If you've fit a nonported cylinder to that crank case, that passage will wind up at a dead end at the base gasket which could result in a leak there during crankcase compression and transfer phase of the cycle. Check out PN 822507 on Strictly Hodaka schematics for the DS 80 for a view of the base gasket and you'll see the corresponding opening on the gasket.

If we are looking at the same thing here, the hole is a vent passage from a crankcase casting void to atmosphere. Looking at the last two photos in that eBay listing, you will see that the passage is continuous with the web reinforced void at the back side of the cylinder and above the transmission area.

The hole is to eliminate pressure build up of a hot engine in what would otherwise be a sealed void. If the vent hole is bubbling under cylinder pressure, you have a leak in the seal between crankcase halves which needs to be remedied. Hopefully you were intending to split the cases anyway. If so, careful rebuild will eliminate the leak.

Help me out a bit here, Jack. While I don't have access to an image of the base of the DS80 cylinder, the appropriate base gasket does have a corresponding opening to the vent passage you've described which led me to believe that this passage is some type of port. Does this passage simply continue through the wall of the cylinder and exit to atmosphere? I apologize if my speculating on the nature of this orifice was misleading.

Okay, let me start over. The reference to the ebay picture was just to show how the hole in mine looked. Mine is a completely stock 1973 Dirt Squirt. I went ahead and removed the intake so I could take a picture of my actual engine. You will notice the hole at the seam of the two crankcase halves just behind where the cylinder sits. I put a piece of wire down the hole and it is just over one half inch deep.

Your 2 engine halves are leaking at least at the hole I do not believe it vents anything anyway leaking engine cases. ------ Clarence

So does anyone know what this hole was for? And any suggestions what to plug it with, since I am not planning to split the cases for this minor leak.

Go back and re-read my last post. I wasn't guessing about the purpose of the vent, and plugging it won't fix the leak, it will just make the pressure go somewhere else. Into the transmission would be the other way out. Or you can just leave it be.

Clarence, don't confuse "vent" here with anything other than pressure relief. It doesn't vent the transmission and it doesn't vent the cylinder. It only allows pressure equalization in the casting void. Without that relief, pressure build up from heat alone could cause the case center sealant to fail which would result in a crankcase leak, as it is doing here, or a transmission leak. Hodaka put these things there for a reason. Those reasons don't change over time.

The vent is in the very bottom of my photo. I am not referring to that. I am referring to a 1/8 inch diameter blind hole 1/2 inch deep almost touching the base gasket. If you zoom in on the picture you can see it.

There has been a lot of speculation about the purpose of the blind hole, but so far no one seems to have come up with an explanation. Regardless, it should not leak. If it does leak the case are not sealed properly, either due to damage or not enough sealant. If it is a very minor leak I am in agreement with Bullfrog that it won't affect operation much, if any. The only concern is that it may get worse over time.

Also, I did go back and look at that ebay photo. The hole that I see goes down about a half inch like mine but then dead ends. I don't see that it is continuous to the void that is vented by the vent. Can you help me see this if I am missing it. thanks.

UPDATE. I found another related thread on the site. Seems nobody there can figure it out either.

viewtopic.php?f=1&t=391&hilit=hole+to+nowhere

H J I am to old to be confused. The drilled hole does not reach a casting void it is just a drilled hole to nowhere. I have been wrong before and plan on being wrong again. The voids vent back into the transmission area. ------------- Clarence

Bingo. That's my conclusion too. Since I have a tiny bit of air leaking out of that hole to nowhere, it must be a little leak between the case halves just enough to feed into that hole. That's why I am thinking of filling the hole with something to just block off the only path out for air. That's the only place I see bubbles luckily. Still thinking of what to put in the hole.

There have been discussions here on the forum in the past discussing the purpose of the "half hole" in each case - which makes a "whole hole" when the cases are assembled. The current "not a guess" about the purpose of the hole is clearly not correct.


You have many options regarding the 1 psi leak down in 3 to 4 minutes. One of them is - do nothing. A leak down rate of 1 psi per minute or faster (starting at 6 psi) is a "FAIL" with repair required. Your results are a "PASS".

Certainly when you do get inside the engine, it would be good to identify the path of the leak and to cure it.

Ed

Hey Ed, so would it be a good idea to fill that hole to stop whatever path the air is escaping through? is there any downside to that I am overlooking. Seems that it can only help but I don't want to create problems either. I was thinking of epoxy or JB Weld but I don't know that I want to make it tough to get apart down the road. So then I was thinking of RTV silicone. Although the test is pressure out, when running the vacuum would be sucking whatever I put in even tighter in the hole.

I wouldn't want to "glue" the cases together with epoxy either. You could put a dab of silicone sealant there if it makes you feel better. It will not "cure the leak", but it will further restrict the actual amount of air moving in-and-out in response to the internal crankcase pressure changes. The dab of sealant will hurt nothing. It will slightly retard the leakage into the engine (which is already negligible) during the vacuum pulse. (Remember, the engine has PASSED the leak down test.) And you will feel better.
Ed

Thanks very much to everyone for the pointers. I love having this forum available. It's a lot of fun working on these great old machines. I will try sealing it tomorrow. Might be the day after before I can test it again, but will report back. Good night.

I really don't expect the dab of silicone sealant to improve your test results much (or any!). You are doing it to feel better.

Don't forget, the engine has PASSED the leak down test.
Ed

Captain, what is on base of the cylinder that aligns with the mystery hole? There is a corresponding hole in the base gasket suggesting its design allows passage from the mystery hole into the cylinder at the base.

On the Dirt Squirt, there is nothing on the cylinder corresponding to the mystery hole. The hole is completely exposed and not covered, even by the gasket.

I wish we could pick the brain of the design engineer so we can learn what the hell the mystery hole is all about and why it was designed that way.