Blown head.

C

chrisme

New Member
So I just got my new head gaskets today. Put one in. Torqued down to 20 Ft-lb and fired her up. Immediately it sounded like my head gasket was blown again. WTF?!?! And I could feel gas blowing out of the front of the head. Upon closer inspection I noticed that where the head gasket blew out before the head is very slightly warped. Maybe 1/10th of a mm. But enough to make it not work :(
So now I have my non-slant head back on. Which sucks. I really want my slant back.
What can I do? Can I have a machine shop grind it down so it will seal again?? I'm really upset about this :(
:-||
 
can you lap the head (sand it on a piece of glass until flat)???
after seeing the old gasket picture, it looks like you have a ton of compression happeneing tho !!!
 
Right now I'm very carefully filing it down. We'll see how it works. If I make it worse, so be it. I can get another one for less than $20 shipped. I just don't want to wait more!!
 
Finish it off with some #300 wet/dry on a piece of glass. I think having a machine shop do it may be a bit too aggressive. Last time I had a head ground at a machine shop they just slapped it on this big inverted belt sander for a few seconds then charged me $30.
 
So I filed it down so that it is all flat. Then I lapped it on glass to make it shiny. But now the piston interferes with the head
I think this emoticon is a pretty accurate depiction of what I looked like when I slowly turned the engine over only to find it interfered.
:-||

good thing I was turning it over from the magnet and not actually started it!!
 
And to top it all off my car has a blown wheel bearing, so it probably has 100 miles before leaving my stranded. And my mountain bike is broken. Both of which I'm waiting on parts that will be here next week. So my MB is my only form of transportation unless I want to walk 6 miles to work. Which I don't. But it is looking like it isn't looking good...
 
Could be worse, your bike could have broken a chain, TSC is 20 miles away and because you've been riding your MB for two weeks straight your truck has a dead battery from sitting. But it's not like anything like that has happened to me or anything. :D
 
So I used aluminum foil to make 2 extra head gaskets. No interference any more!!
Except running wicked high compression. I was going up the steep hill to my house and it started running like crap. I could feel it getting hot. I hit the kill button, and it kept running for about 5 seconds, it even let me rev it up a bit!!! Then finally died. And yes, my kill button works fine. So it was basically running completely on pre-detonation. I'll try some high octain and see if that fixes it. If it does, it will probably have a lot of power!
 
Kevlarr said:
Could be worse, your bike could have broken a chain, TSC is 20 miles away and because you've been riding your MB for two weeks straight your truck has a dead battery from sitting. But it's not like anything like that has happened to me or anything. :D
Click to expand...

Funny you mention that, some thing happened to me. Chain didn't break, but the master link came apart, and it wasn't worth getting a new 415 link because the chain was in horrible shape. But my car's battery was dead (like usual...). I park it on a hill though, so roll down, pop the clutch, and I'm good :)
 
chrisme said:
Funny you mention that, some thing happened to me. Chain didn't break, but the master link came apart, and it wasn't worth getting a new 415 link because the chain was in horrible shape. But my car's battery was dead (like usual...). I park it on a hill though, so roll down, pop the clutch, and I'm good :)
Click to expand...

reccommended torque for the head is 10 lbs per inch...20 might pull your head bolts out of the cheap threads....over torqueing can cause warpage...Dennis
 
I thought it was 16lbs. I do 20 because of the extra compression of the slant. If I break the studs I'll just re-tap with 1/4 20 like everything else. Much easier to find nuts and stuff.
Actually, if I were to re-tap the head I'd get whatever is close to 8mm in standard. As much as I hate standard, it's all I can get it my little town.
 
chrisme said:
I thought it was 16lbs. I do 20 because of the extra compression of the slant. If I break the studs I'll just re-tap with 1/4 20 like everything else. Much easier to find nuts and stuff.
Actually, if I were to re-tap the head I'd get whatever is close to 8mm in standard. As much as I hate standard, it's all I can get it my little town.
Click to expand...

i have a 80cc and i put a slant head i bought from zoom...its torqued at 12 lbs...and its fine...you wouldnt break the head bolts you'll strip the threads...go on normans site and ask him what to torque your head bolts at...just tring to help...good luck...Dennis
 
I'm not really very worried about what to torque them to. What I've been doing works fine. If I strip them out I'll just replace the studs with something better.
Right now I'm glad that straight filing my head fixed it.
What I need to resolve is the compression being WAY to high.
 
One of my slants was also warped and blew gaskets. I went back to standard head and will have a machine shop fix it for me.
 
chrisme said:
I'm not really very worried about what to torque them to. What I've been doing works fine. If I strip them out I'll just replace the studs with something better.
Right now I'm glad that straight filing my head fixed it.
What I need to resolve is the compression being WAY to high.
Click to expand...

File the top of the piston? :D
JK!
 
Just about all the $15 slant heads I have seen from Zoom have a pretty large divot on the leading (or trailing) edge. Filing sounds a little......harsh.....I just got on mine with some progressively finer wet/dry paper (I think I started at 180 or something).

Then I painted up a new head gasket with aluminum paint.

Torqued to 16-18 FT-lbs, which is perfectly fine for good M8-1.00 studs.

Sealed tight.
 
Last edited:
So with only one gasket the piston and head were interfering, but with 2 gaskets I had less compression, or about the same as the normal head. So I filed the head down a bit more, then lapped it again. Using 2 head gaskets and I have about the same compression, maybe a bit more, than I did before with the slant. Works great! Took it for the test ride from ****, WOT about 3 miles to a big hill, WOT up the hill, and back. If it doesn't break down on that ride, and I don't have to pedal assist up the hill, that means it's running well. LOL. maybe not the most scientific test ever, but it works.
 
Ok uh Pablo 12 ft pounds is 144 inch pounds. Typo? Reading this ya you shouldn't break the 8mm studs but you might pull the threads out of the aluminum block with 20 ft. lbs of torque. Also you can make the cylinder go out of round with too much torque. Just a suggestion. If you take the wrench with you, snug them to 10lbs. Then ride at WOT for a couple miles, stop and re-torque the heads bolts to 10-12 ft. lbs. again while it's hot. I even lapped the top of my cylinder on a piece of glass while I had it off to replace the base gasket. The cylinder was already very close to flat but the head took about 10 minutes with 120 wet/dry and alot of water to get it flat.
 
Hahahahah yeah - ft lbs!!

I've gone to 20 and no damage, but good point. No good sealing flat HT head/cylinder should need more than 16-18 ft lbs.
 
donuts31 said:
One of my slants was also warped and blew gaskets. I went back to standard head and will have a machine shop fix it for me.
Click to expand...

Mine blew the gasket, and if I hadn't kept riding it, probably wouldn't have warped. I wish I could have taken a pic, it was like someone just took a very small sliver off the head. Anyway, it will be cheaper for you to buy a new head than have a machine shop fix yours. Just file it down enough you can run 2 head gaskets with the same compression. And call it a day.
 
You must log in or register to reply here.
Back
Top