99 Toad Cylinder failure!?!?

[jakecb420]

So, a little back ground......the engine was rebuilt first with new seals and bearings. I did some exhaust bridge relief work that lasted a few hundred miles before the piston got chewed up by possibly the top ring catching on my poor work. I then redid the top end with a .20 over piston, and had the local mc shop do the boring and relief work. Put it all back together, and road it for another couple hundred miles. Just last week I noticed that I had to ad transmission fluid, not the first time, and I don't have any visible major leaks.(little seepage at the clutch actuator). I also noticed my revs were hanging on a little than usual. I figured I'd do a leak down test to see how things are holding up. NOT GOOD!
I definitely wasn't expecting to see the cylinder leaking from both sides of the exhaust port, kinda tucked down inbetween the fins, there is cracks on both sides. I don't really see anything on the inside of the port. Here are some pics I took last nite. Let me know what yinz think.

FYI. I always use a digital snap on torque wrench for torquing the head down, just in case over torquing is on someone's mind.

Also, if anyone wants better pics, I may try to get a few tonite.

[viclioce]

Wow! Looks like you're getting another head! There have been plenty on eBay recently so I would check there first. It doesn't look like it's an over torque issue. More like metal fatigue. After all it IS 41 years old! You may have had minor stress cracks in it before the bore & new piston/rings, and the higher compression from the new setup just did it in! Here's a few eBay links! ; D Victor

http://m.ebay.com/itm/Used-Hodaka-100-R ... nav=SEARCH

[viclioce]

Another.... ; D Victor

http://m.ebay.com/itm/UNKNOWN-HODAKA-RO ... nav=SEARCH

[viclioce]

And another! ; D Victor

http://m.ebay.com/itm/Vintage-Genuine-H ... nav=SEARCH

[Bullfrog]

Zowee, I've never seen that before. Note that it may be completely un-related to the loss of transmission oil. Let me explain.

General, long distance, photo diagnosis is that those cracks are stress/fatigue cracks relating to the forces which come about from the attachment of the exhaust system. The cracks MAY (repeat MAY) be only in the alloy exterior of the cylinder and they MAY (repeat MAY) not be repeated in the cast-in iron liner of the cylinder. Still, it is a serious situation and deserves hands on inspection by an expert.

Note that bubbles showing up there COULD (repeat COULD) come from crankcase pressure entering the bottom of one of the cylinder stud holes in the cases, up the stud threads into the stud passage and finding its way to the miniscule space between the iron liner and the alloy exterior casting - then thru that interface of the iron liner and alloy exterior casting - and coming out at those cracks. IF (repeat, IF) that is the case - simply sealing up the threads at the bottom of all the cylinder studs MAY (repeat, MAY) stop the bubbling at those cracks. Why am I telling you this? Because, IF you get the bubbles stopped at those cracks . . . you may find that you have bubbles at the clutch side main seal (which would explain why you have been losing transmission oil).

I don't know whether or not the cylinder can be saved - but it will need TIG work if it can be saved. THE critical question is whether or not the iron liner is also cracked. If the liner is also cracked . . . I'd say the cylinder is toast.

Ed
PS: Nothing I see here suggests that the head has anything to do with the situation.

[DGardner]

It's hard to see from the photos.... Is there a casting flaw in the cylinder?

[olddogs]

I have seen this same failure on the intake side of an Alumiferic bonded, iron lined cylinder. It was on a Super Combat and went from the right rear cylinder stud passage to the lower right intake stud. It almost looked like the aluminum shrunk and separated or cracked during casting. I made one attempt at fixing the air leak, unsuccessfully, and sourced a different cylinder. Fried parts are expensive and getting harder to locate, and replacement cylinders can usually be found cheaper than new pistons.

[Bill2001]

Good analysis, Bullfrog. Remember that iron liners and cast-on aluminum fins rarely have problems, but since aluminum has 3x the thermal expansion rate of steel, debonding could occur. Just thinkin'.

[michael_perrett]

The cylinder in question will arrive at the Super Secret Hodaka Research and Meditation Center for the ANF annual ride on September 9th. The personal here will closely examine the specimen and do an analysis on where the proper dispersal of the said part will go, the scrap iron bin, scrap aluminum bin or the mixed aluminum bin. Until then, minds can only wonder.
Mike Perrett
ECHJYA pension fund manager

[Bullfrog]

Don't forget the possibility of the Collector's Office Supply Outlet - would make an excellent pen/pencil holder!

Ed
PS: I'm glad to hear there will be a "hands on" inspection by an official from the Super Secret Hodaka Research and Meditation Center!

[viclioce]

Oh crud! I need to pay better attention to the photos. With an exhaust port in the photos, I don't know why I was thinking a cylinder head instead of a cylinder! Let us know what the SSHRMC says about it. I may have a cylinder for you! ; D Victor