Head gasket issue???

[viclioce]

OK. So I’m trying to trouble shoot my 90 psi compression issues. I’ve sent the cylinder/piston/rings of to Terry & Hodaka Dave.

However, after recent disassembly, I happened to notice that the head gasket has no impression in it at all! I thought when you torqued the head down it press a grove, of sorts, into the aluminum gasket? When I pulled the top end apart, I noticed no impression in the head gasket at all!

I also checked the part number on Terry’s website for the Model 99. It says 992501 and my head is stamped 9?2501, the ? being not readable. IF it’s a 992501 it’s a RT/DS head. If it’s a 952501 I believe that would be a Combat Wombat Head! Man, the stamping could be showing the ghost of a 2nd digit 5.....

Here are photos of the head & gasket after removal & a pic of the part number stamped on head? Any thoughts or ideas appreciated! Victor

[Tether]

I have a head with the numbers just like yours with a block where the 2nd number should be. I determined that it was probably a 100 head based on the diameter of the combustion chamber and the bolt pattern.
If you suspect your head is bad I’ll let you have mine if needed.
Bob

[viclioce]

Bob. I don’t know if it’s the head. Was just curious about it not putting any crimp or ridge or whatever the correct term is, in the head gasket.

Initial suspect was the bore was too loose for the piston/rings purchased. I was told by the seller it was a .020 over bore on the cylinder, but the bore appears to be tapered, with it being wider at the bottom, which I believe is an indicator of wear & it not being a fresh bore. Have to wait to hear back from Terry & Hodaka Dave.

I’ve done some searching on eBay & yes it appears that this is the correct size head and the proper one for the Road Toad. And the top of the head measures 50mm across so it’s not a 125 head. Victor

[viclioce]

Just one more thing to look at. It appears the head bolt holes in the head gasket didn’t quite line up. Here’s a photo of the gasket, showing where a lip developed because the bolt pushed it. It likely was pushed it down into the hole, but is this something normal to see? Could this bit of lip set the head off kilter, causing blow by between the head & cylinder surfaces? Victor

[thrownchain]

Set the head gasket aside. Put the head on top of the cylinder, push on it on opposite sides and see it rocks at all, it it does the head isn't flat and will need machining. As for making a ridge in the head gasket the top of the cylinder and the bottom of the head should be flat and parallel so there are no protruding areas to make a dent in the gasket.

[taber hodaka]

I hand lap my heads sandpaper on glass, ------------- Clarence

[dcooke007]

The head gasket protruding into the opening around the head bolt is not normal. The head gasket bolt holes are not equal distance from each other. Head gasket could have been installed 180 degrees out of position to cause this. Again "could have".
Danny

[Bullfrog]

It doesn't appear to me that there are any issues with the head or head gasket which clearly would cause (or reveal) a head gasket leak. The deformation around the bolt hole isn't ideal - but isn't at all likely to cause a leak. I didn't see any evidence of "blow by" on the head gasket or head surface (of course that may have been wiped off prior to photos). Was there any evidence of "blow by" at the head gasket? (One tell-tale is oily dust collecting on the fin surfaces near a head gasket leak. Did you have that?) I'm placing my bet on the old bore, piston and rings being the cause of the low compression.

Of course it is easy (and recommended) to do a quick lapping operation on the head to check it for flatness . . . and I recommend checking to see that all four cylinder head nuts exhibit the same depth of threading. I've bumped into a nut which was not threaded deeply enough. It would "jam" on the stud then accept torque up to the published spec. (170 in. lb.) - all without ever coming down tight on the cylinder head. That caused repeated problems till the flawed head nut was discovered. And yes there were signs of a head leak, two signs in fact. Oily dust building up in the vicinity of the leak . . . and a seizure! Dagnabit!
Ed

[viclioce]

No dusty oily signs Captain. I will check the bolts to see that they all tighten down on the stud threads the same distance. I can do that now while the cylinder is out.

Thrownchain the cylinder is not here right now, it went to Terry & Hodaka Dave.

Dan, thankfully I have spare new gaskets. But it seems like it’s the gasket itself which was not lined up. The holes do not center on the holes on the head no matter what position the gasket is placed.

I just don’t understand why there is no pressed in ridge on the gasket. I’ll wait to hear from Terry/Dave & see what’s reported as issues found with the cylinder.

I guess I’ve been lucky so far. I haven’t had these kinds of issues with the other bikes. Everything just went together smoothly. Just one more hurdle to overcome, I guess? Victor

[viclioce]

Ed. Looks like I can rule out a bat head bolt! They all seem to go down evenly and to the same point, without the head in place. Victor

[Bullfrog]

OK! That looks good on the head nuts.

That machined ring-groove on the head is not intended to "imprint" on the head gasket - but it does indeed have a scientific seal enhancing purpose.

Discussion:
1. Imagine how much pressure would be required to compress ALL of the surface area of the head gasket to cause some "cold flow" of aluminum into the ring-groove. It would require an extremely "stiff" head (like say, steel or cast iron) to stay flat while compressing all that aluminum AND a whole lot of pressure to get the imprinting job done. (and that kind of pressure isn't necessary for a good seal)
2. The "ring-groove" provides an interruption in any leak path which might develop at the bore edge of the head gasket. Any gases traveling "out" from the edge of the bore would hit that groove and then those gases would pressurize the volume of the groove to full pressure BEFORE they would "try" pushing further to escape to the outside world. By the time the ring-groove reaches full pressure, cylinder pressure will be dropping . . . and leaking to the outside world is either delayed or prevented altogether.
Ed

[matt glascock]

Hi Victor, Two things. First, sorry about getting jammed up all day today. One thing after another and I'm still at it. Maybe tomorrow afternoon? Second, on the photo of the deck in the lower left hand corner there is something causing shadowing near the stud. Is that just adhesive of some sort? Might want to clear that off before it falls into the crank case and causes further mischief and mayhem.

[thrownchain]

Looks like a small divot in the base gasket.

[viclioce]

Wow Matt! Good eye! I’m guessing it’s a small piece of the bottom end seal, which is still on the base, but I’ll check it when I get home! The wife & I went to my mom’s in Albuquerque for a piano recital. Now we are going to take her out to dinner. I’ll get home later this evening. Victor

[matt glascock]

Agreed. Probably lifted up when the jug was pulled. I just looked at it on the good computer - higher resolution. Couldn't see it well on the lap top.