Blown Headgasket

[sootman73]

I've done a couple searches on here but I haven't found an answer to my question. I know my head gasket is blown but I'm curious as to what causes this to happen? I had Jeff at FAST do a port, bore, got a milled head from him, and added a timing plate set @4 degrees BTDC.

 

Is it usually over heating that causes this? Running down the road at home after break in period it would warm up pretty quick but only to 180's. A memorial day weekend at badlands and I had temps that shot to the 240's a couple of times and peaked at 249 once. It went up so fast that i didnt even notice it. 

 

Anything I need to worry about putting a new gasket in and buttoning it back up? (I was gonna check the head for flatness and square first.)

[sheerider11]

Yeah why did it get that hot that fast?

[sootman73]

Well thats what i'm not sure. I suspect the head gasket was blown and caused the rapid overheating. The water pump is not broken and turns with the crank. it spit coolant out a couple of times hours before i hit the high temps. It was only at 190-200 degrees when it did. Though this thing has always spit coolant no matter which rebuild.

 

I am going to take care of the heat problems as i put it together.

[Strm Trpr]

Where do you want to start?

Did you pull the head yet?

If not, do a compression test and find out which side blew.

If for some reason you were too lean, detonation will occur and increase combustion pressures exponetially and lift the head and/or warp the head and blow the head gasket.

Too much timing will cause deto too.

 

Many reasons will cause a blown head gasket.

Find out what side blew and go from there.

An air leak between the cylinders and reed cages, and/or between the intakes and reed cages will also cause you to run lean.

Torn intake boots where the x-over tube connects is also another spot to check for cracks.

 

Did you set your floats in your carbs to 20+/-1mm?

Are your carbs tuned for your build?

91 octane?

Jetting?

 

 

[WINDYCITYJOHN400]

Lean jetting gets my vote.

 

List your main jet/pilot jet/needle clip position/air screw settings

Edited June 4, 2014 by WINDYCITYJOHN400

[sootman73]

i knew which cylinder it was while riding because it was pushing coolant into the cylinder when it shut off. 

 

Here are some pics of the gasket, its easy to see where it blew. it was jetted rich as well and that's probably why there is zero damage to the cylinder walls. (crosshatching still present everywhere)

 

 

 

 

[sootman73]

I'm leaning more towards old radiator, worn out cap, and just not enough cooling for the power the build is making now. Does it look lean to you guys? granted the plugs are dirty after a long weekend of riding.

 

I thought i would need a lot of tuning with the new build but once carbs were synced i only jetted up one side and it revved perfect.

[WINDYCITYJOHN400]

I'm leaning more towards old radiator, worn out cap, and just not enough cooling for the power the build is making now. Does it look lean to you guys? granted the plugs are dirty after a long weekend of riding.

 

I thought i would need a lot of tuning with the new build but once carbs were synced i only jetted up one side and it revved perfect.

It's NOT your cooling system. (I make well over 100HP with my 10mill cub.) The stock cooling sytem is fine. 90% of heat issues are jetting related.

Motors rev great lean........right up till they don't. LOL

[Strm Trpr]

Cut the threads off those spark plugs right up to the washer so we can see the smoke ring.

I bet the left plug came from the cylinder that blew.

That plug is way lean.

Does the head have any damage?

Check the float heights in both carbs.

Set them to 20+/-1mm.

The right cylinder has an air leak or fueling issue.

[sootman73]

Thanks guys, I'll chop the plugs tonight and post it up. I'll also grab my jet sizes and carb settings while i'm at it.

[sootman73]

Finally got around to this, I hate July at work.

 

I got a new gasket, threw it back together, upped my main jets two sizes (see below) and then did a plug chop after a 6gear wind out

 

 

Main Jet: 320

Pilot Jet: 25

Needle: 3 position

 

Do i need to richen up a little bit yet? def doesn't get on pipe as easy as before though

 

Let me know what you guys think

[n2otoofast4u]

Pilot is lean IMO

 

Not knowing the rest it's hard to tell on the main, but a 25 pilot to me is lean near everywhere with your mods.

[sootman73]

After looking around at pilot sizes it does seem a bit lean, though it starts and idles perfect at any temp.

 

should i grab 27.5 and 30? How can you tell if they are lean during tuning?

[tfaith08]

I'm a tad lean with 320s running T5s and UNI w/o lid. There were no airleaks as of the plug chop.  Your elevation is only about 600' higher than mine.  I'd get some larger mains since you're running ported cylinders.

 

Is your airbox lid off?  What filter are you running?  Did you do a leakdown test? 

 

Get both the 27.5 and 30.  They're cheap enough to have both.  Shipping will likely cost more than a pair if you order twice, so get a pair of both sizes the first time. 

 

I'm never one to give this answer, but any and all jetting questions are best answered by searching.

[EaCastillo00]

if your radiator is spitting the coolant, its definetly the gasket, its probably al toasted because its old or something, or its to thin, the radiator spitting thing its because your gasket isnt doing its job probably not sealed correctly and its letting the compression through to the coolant, and basically its boiling and evaporating it because its too hot :/