Kodiak yamaha is blowing air out of intake

[Clayzimmerman]

So i replaced the head gasket on my kodiak yamaha and it is not starting i checked and made sure it had spark and was getting gas and then i noticed that it was blowing air out of the intake. i checked the exhaust and i can hold it shut with my hand but i cant hold the intake shut. Any idea what is going on?? Thanks 

[Mech]

I think you should check the cam timing..

 

[Clayzimmerman]

Ok thanks

[Clayzimmerman]

I checked the cam timing and it was off pretty bad. I had forgot to fix the timing when i put it back together but now the timing is perfect. It still wont start. it cranks better and smoother though. Anything else that could be wrong 

[Mech]

You might have bent a valve.. Has it got compression now?

Is it firing at all, trying to start, or nothing happening at all ?

You could try starting it, then take the spark plug out and check whether there is fuel getting on it.. Then attach it to the lead, rest the plug on the engine, and watch for spark while you crank it over.

 

[Clayzimmerman]

How would the valve become bent? i’ll check it out tomorrow. When i checked the spark plug before the timing was correct it was sparking. Could i have messed up the carburetor by having the timing off?

[Mech]

The carby should still be fine unless you were trying to get it running by adjusting the carby.

If the cam timing was off by very much at all, the valve can be being held open when the piston comes up, then the piston hits the valve and it bends the head of the valve sideways..  Bent valve.  It happens !

Take the sparkplug out and put your finger in/over the hole, kick the engine over and it should blow your finger out with force. If you can hold your finger in there.. you have not got enough compression.

[Clayzimmerman]

Alright i’ll try that tomorrow. Thanks for the info

[Clayzimmerman]

I pulled the spark plug out and it had fuel on it. I can hold my finger over the hole pretty easily. I guess that means a bent valve?? 
Is that hard to replace? i’m kinda a newbie.
 

[Mech]

You need to pull the head off again obviously, then you'll need a spring compressor, or a friend that has one you can borrow to get the valves out,  then you need one or possibly two new valves and they need to be "lapped in", which you do using something called grinding paste. You can buy grinding paste in small tubs from an engineering supply shop, and they will also be able to sell you something called a valve sucker.. that's what we call them here in N.Z. anyway.. It's to hold and work the valve when you are doing the lapping in. It would be a good idea to get the manual or have a read up on valve lapping.. it's simple but needs pictures really to show what you are trying to achieve, which is an air tight seal of the valve.

When you've done the lapping in, it's really important to clean and oil the valve seats before you put it back together, they need a hard rub with a damp cloth to get the abrasive compound dust out of the metal seat, and, you need to drop the lapped in valves into place, flip the head upside down and fill the combustion chamber with petrol and make sure that the valves are sealing totally.. If you get the result shown in books they should be right.

Then you need to fit new valve guide seals, lube everything and put the valve springs, with the metal washers that go between the springs and the head(very important, look for them when you are taking the valves out or they can get lost), back on. The valve springs are held by little tapered wedges which can get lost easily, especially as you let the spring compressor off as you are assembling, so make sure they are properly seated, and keep your hand over them as you let the compressor off.

Once the head is reassembled  you are back at where you were when you did the head gasket.. Take care to get the cam timing right, get everything absolutely clean, especially all the sealing surfaces, and you should be right.

Get a manual, they are free to download off here, and have a read about the valve lapping, or google it and have a read up with pictures.

[Clayzimmerman]

Hey thanks alot for the info. I tore the head off and found that the valves look fine but that when the piston hit the valve it pushed the valve straight up and broke the connecter above the valve. I dont know what its called but is it a hard fix looks like it could be…

It was the exhaust valve connection that was broken so i guess that was what was causing air to back up. The intake valve looks great

[Mech]

You should flip the head over and fill the combustion chamber with petrol and see they don't leak.

The part that broke will be called a rocker arm probably.

 

How far from the edge of the piston was the valve mark on the head ?

If it's near the edge it can effect the rings.

Was it much of a dent ?

[Clayzimmerman]

The valves do not leak. The mark was about a quarter inch or more off the edge of the piston. There was a decent dent on both the exhaust and the intake side. 
Is it hard to replace rocker arms??

[Mech]

No, find the bolt that holds the shaft they pivot on, take it out, and the pin will pull or push/tap out...  I'd think.. There will be washers and springs.. take note.

It would probably be best to get a set of arms. They are probably made to break and have a thin place on them, look around there for fatigue if you want, but I'd get a set.. They would have all been close to breaking if both valves hit and made similar dents.

Hopefully they did their job and saved anything more major. There are a lot of cars with rockers like it and the precaution seems to work fairly well.

[Clayzimmerman]

Ok thanks 

[davefrombc]

Just my  2 cents in , but if there  are  "decent dents" in the piston, check it  very closely for cracks too

[Clayzimmerman]

Ok i’ll do that

[Mech]

Yeah there is some danger there as Dave suggests. It's also possible that the top ring lands on the piston could be pressed down, clamping the rings.

That's why I asked how far from the edge. Perhaps a picture would be a good idea...

If you are sure the valves aren't leaking, then they didn't get much strain on them, they bend really easily.

 

[Clayzimmerman]

I’ll try to get some pics tomorrow. Sorry i cant right now…

[Clayzimmerman]

Ok so i checked the piston and there is a dent only on the exhaust side. They factory indentions are bigger than i remember them being when i had looked at the piston earlier. That caused me to believe that the valves had deepened the dents. According to the pics online the dent is small. 
I checked for cracks and there are none.

[Clayzimmerman]

I got a set of rockers coming in Wednesday so i hope i can get her up and running soon