Actual Blown Headgasket

Wow, I have never seen that on these motors. Thanks for sharing with us.

if your head bolts were a little loose, that was probably it. the hot gases will exploit any tiny opening and attack it till it fails.

lucky that's all that happened, though.

Junster said:

UPDATE; I couldn't stand to wait for a new head gasket. I went to the hardware store and bought a short piece of alum. dryer vent. After destroying a couple attempts with a drill I finally used my air grinder with a 3/4" sanding drum and sanded out a very nice round hole for the cylinder (used the bottom of a caulking tube to mark the hole just the right size). I have a extra bottom gasket I keep just for marking the bolt pattern. Again punched the holes small with a drill then with a pointed grinding bit relieved them out to the right size. Coat of spray copper head gasket sealer on both sides and good to go. Oh while the head was off I lapped it in again on a piece of glass. This is the second time. It was heat warped again. Took about 3 minutes to get it flat. I'll be buying a billet head from Pirate Cycles as soon as Jim resupply's them.

Click to expand...

How do you do this lapping on a piece of glass thing?

Pat

Very lucky it was an easy fix Junster, my engine came with no head gasket installed.... But came with 2 "spare" head gaskets haha. I did not realize it was missing and did not have a problem at all but once I noticed it was missing I put one in ASAP.

Junster said:

Oh while the head was off I lapped it in again on a piece of glass. This is the second time. It was heat warped again.

Click to expand...

My head is leaking again TOO. This is the cause. My slant head and vigorous lapping has increased my compression greatly. The price to pay I guess, but my head was NO WHERE NEAR FLAT AS RECEIVED.

For the fellow who asked:

One piece of flat glass 12"x12" or whatever.
A plywood surface or towel on concrete outside (work surface that you can get wet and dirty)
Various grades of wet/dry sandpaper (rougher for material removal) all the way up to 1200 for real smoothing.
Water.

Set your glass on a towel, lay the sandpaper on the glass, get the whole affair wet. Then rub the mating surface of the head in a circular pattern as required while holding it as flat as possible. Progress up to finer grades of paper and clean the whole affair at each grit change.When complete, wash the head very well. You don't want grit in your engine.

to add to Pablo's instructions, turn the head a few times while doing this, i mean how you're holding it. like, if you've got your fingers on all the bolt holes and you're pressing down, rotate the head so your fingers are on a different set of bolt holes every so often.

this way you'll keep an even pressure on it, and won't end up sanding it on an angle.

also, i just use masking tape and tape a piece of 600 grit down to a piece of glass, and use that. on a Grubee head, there's circular marks from where the factory surfaced it, and i keep sanding till they're gone.

you can lap it a little just to create a smooth mating surface, or a lot to increase compression. just don't go overboard, it doesn't take a lot. a coupla millimeters is enough.

another thing to keep in mind, is higher compression makes it harder to start, meaning more pedaling.

one more thing. my head is lapped about as much as possible, and the compression is way more than stock, and i've been beating the he11 outta my motor for 6 months, and a few thousand miles with no problems. i guess it's a hit or miss situation.

The correct way to lap is in a figure eight pattern. 300 grit should handle the whole process. You will get a 10 micro finish no problem even dry. Wet sanding and going for a mirror finish is just gilding the lily. Hey knock yourself out if it makes you feel good but I prefer to work smart not hard. Wet sanding is generally only a cosmetic process.

If you have a nice cross hatch that feels smooth when you run a finger nail over it your there. Running a graphite pencil tip over a surface is another improvised test for micro finish.

quite possible that the engine was running on the lean side to put so much heat into the gasket.

I've done 6,000 kilometers (3,700 miles) and i've reused the same head gasket 5 times, with no heat related problems.
I'm surprised at how well those aluminium gaskets seal, even when they are reused multiple times.

Having said that, the gasket does ooze filthy black goo, but no more than the base gasket or the case gasket.

Fabian