Exhaust Leak from Rear of Engine- Under Carbs

Hello Everyone,
I have a strange scenario. It seems im getting exhaust/air fuel mixture leak from the rear of engine, under the carbs. Its the area in between the jugs. I am under the impression that the air/fuel/exhaust mixture is entering through the engine stud, and down the area to the rear. I am attaching a picture of the situation.

The intersting thing is that no oil is coming out, only exhaust/air and fuel.

The exhaust is coming out in the picture in the dark area right before the cam chain tensioner. Its the dark area. Thanks everyone.

Anyone come accross this before?

Any fixes?

Thanks everyone.

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Took me a minute...the pictures are sideways. Remove the oil filler cap and take a sniff. Smell like fuel?

Gary H.

 

maybe cracked jug ? or bad head gasket? you know any one with a video scope?
you could get a good look . walmart sells the scope for around $80
automotive guys use them when they do smoke tests on evap systems

 

Sounds like a blown head gasket to me. If you can find a leak down tester to pressurize the cylinder that should confirm your problem.

 

OP says and is showing the leak at the head to block. Possible blown gasket there and a sticking float causing fuel in the crankcase?

Gary H.

 

po did not say fuel in the crank case he said ""The intersting thing is that no oil is coming out, only exhaust/air and fuel.""

you did advise him to " Remove the oil filler cap and take a sniff. Smell like fuel?" which is good advice

 

you advice to check oil was good no need to STFU. he should check that.
problem with forums is sometimes hard to intereprit statements made, , with every ones 2 cents op will have a dollar and a fix for his problem

 

That's ^ true too. Lol.

Gary H.

 

From the picture it looks like exhaust is blowing out from under the head.

I have never seen that before but if you have a cylinder with liquid fuel in it

that would either bend a rod or blow a gasket. I would take a blown gasket

any day over a bent rod for sure. If that is true that shows how important it is to

maintain the carbs and petcock so the cylinders don't fill up with raw fuel so you

don't get a hydrolock situation.

MN

 

Isn't that area on the side of the tensioner open to the front of the engine (too lazy to go look at mine in garage)? I'm wondering if you have a leaky exhaust connection and you're feeling the pulses of air coming through that passage way.

 

Thank you everyone for your input. Jayrodoh, I thought the same thing. Then I proceeded to stick rags between the jugs so that it isolates the exhaust ports. I still had the leak...
Very weird situation for sure. The bike runs fine... It pulls, but wont idle. I am planing to do a compression test soon. Strange thing is that there is no oil, I would assume that if my gasket failed, then it would cause oil to seep out as well. I did just replace the gasket with a athena gasket, and found this issue upon my re-install.

Thanks everyone. Input is very appreciated.

 

I would like to add that it really seems that the air is coming from UNDER THE GASKET. Its difficult to tell, but when I stick my finger in that port right next to the stud that travels all the way up top and holds the engine together, I can feel the exhaust pulses.

Such a strange situation. Sucks cause I just took the engine apart, and put it back together... and now its winter...

 

Just replaced the head gasket with an Athena gasket. Well that is more than likely the issue. Something didn't get back together right. Pull the head back off. Check to see what happened and have the head checked for warped sealing surface. A blown head gasket may or may not leak oil.

 

Hello Everyone.
I know this thread has not been active for a while, but I thought I would give a update in hopes it may help someone in the future who is in a similar position as me.

I bought a top end kit and I rebuilt the top end, with a new gasket. I re-surfaced the head and took off 3/1000 of a inch at a machine shop. After rebuilt, the bike starts, but I get a very small leak at the same exact spot....

I will go back into the engine and re-surface the engine block now. I am pretty sure that has to be the culprit.

My advice for anyone who will attempt this is to also get the engine block checked.

Anyone experience block warping on the forum? Any input would be appreciated.

Thank you everyone for reading.

 

The cylinders should not warp but anything is possible including poor maching from the factory. Don't trust anything for warpage unless you can use a machinists straight edge and a feeler gauge to see how far the warp is. Resurfacing the cylinder to head mating surface should clear up your issue.

MN

 

Who's gasket? Not all gasket kits are the same, and some just plain don't work correctly.

 

Check out my head gasket thread. I had an issue with my cam tunnel gasket, curious if you had a similar issue.

Head Installation Sanity Check | XJBikes - Yamaha XJ Motorcycle Forum
http://www.xjbikes.com/forums/threads/head-installation-sanity-check.69186/

 

Did you buy this from Chacal? If not buy a oem head gasket from him.

Gary H.

 

Have the carbs been thoroughly serviced ?

Have the valves been adjusted?

Have you done a compression test?

 

Does the through stud have a thick washer under the acorn nut? Are all the nuts torqued to spec in proper sequence (after a re-build the nuts should be re-torqued after the bike has been ran for a few miles at operating temp).

Gary H.

 

+1 on the compression test.

 

In addition to everything else listed... Some random thoughts:

Gasket and mating surface on can chain tensioner? Off the top of my head, I believe there is a rubber o ring too.

What about your valves and valve seals?

Blocked exhaust?

 

What about the gasket below the jugs too?

 

He'd have oil weeping out, and only just a little unless one of the oil gallery o-rings was compromised. There's no compression on that side, just air pumping thorough the crankcase breather.

 

+1. I had to replace a set of aftermarket o-rings because they didn't seal like the oe rings.

Gary H.

 

All the acorn nuts have washers under them and were torqued in proper sequence.

For some reason, this is not sealing properly. I am thinking that it may be either to the cam chain tunnel gasket, or my engine block being warped.
What is the likely hood of block warpage? Does anyone have any experience with that?

Here is a different thread that has a lot of good information on a almost identical problem to mine.

http://www.xjbikes.com/forums/threads/head-installation-sanity-check.69186/page-2

 

Almost zero, but it's easy to check with a straightedge.

 

Hello Everyone.

I took the head off again. This time, I took the engine block of also.
When inspecting the head gasket just installed, I can see dark areas going into the cam chain tunnel. This is from me running the bike for 10 minutes and seeing the same issues as before. I am 99% sure that the culprit here is the cam chain tunnel gasket that came with the kit. It is too thick and prevents proper sealing of the gasket.
This is underscored by the dark areas in the head gasket going into the cam chain tunnel. This is due to compression loss. The compressed gasses escape into the cam tunnel since the cam tunnel gasket is TOO THICK. Therefore, the gases escape into the cam tunnel, and out, to the area behind the carbs.

This may lead to over heating, and warpage also.

Thank you everyone for paying attention to this thread. I hope in the future this helps someone out. I would like to thank jayrodoh for his thread. It was a great help.

 

It sounds to me like you got it figured out. Athena usually supplies gasket kits that are exact to OEM specs. It's concerning that the cam-tunnel gasket was too thick.
I'm assuming that you dod not buy the gaskets from Chacal. Is that correct?

 

Ill have to go back and look---- but I seem to recall that Len had put a note out on his page somewhere about cam tunnel gaskets and getting the right ones.... Etc......

 

Glad you found it

 

I had this exact problem with my 81 750 and I found it to be a bad head gasket as well as my piston rings being out of spec the dirty bit on your bike looks darn near identical to mine