Cylinder head advice

[garyr]

I have a stuck exhaust valve on my 78 XS 650, 750 conversion. The valve works but wont close the last 1/4 inch. I have to take out the engine and take the head off and have the valve guide changed.

My question is; when you take just the head off, do you need to also replace the base gasket if you don't touch the cylinders. The engine has about 2k on it since a 750 conversion.

Thanks, Gary

 

[Bob Wegman]

I have a stuck exhaust valve on my 78 XS 650, 750 conversion. The valve works but wont close the last 1/4 inch. I have to take out the engine and take the head off and have the valve guide changed.

My question is; when you take just the head off, do you need to also replace the base gasket if you don't touch the cylinders. The engine has about 2k on it since a 750 conversion.

Thanks, Gary

I don't see why you would need to replace the base gasket. If you happen to damage it when removing the head because the cylinder stuck to the head, then you would need to replace it.

 

[Wingedwheel]

It’s cheap and if you pull the head you should replace your base gasket as well. Why take a chance?

 

[5twins]

If you don't break the "seal" (allow the cylinders to lift off the block), then I don't think you need to replace the base gasket.

With the valve not closing all the way, that may indicate it's bent. To determine if it is, chuck it up in a cordless drill and spin it. If it's bent, it will be quite obvious (it will "wobble" all around, lol).

 

[jetmechmarty]

Is your base gasket green?

I don’t think you can replace the base gasket without breaking the chain.

 

[Jim]

Is your base gasket green?

I don’t think you can replace the base gasket without breaking the chain.

Yes, if it's a green Athena base gasket, replace it while you have it down.

The XS-1 jugs require breaking the chain. Your '78 will come apart with the chain still intact.

 

[Its been a long time]

My thinking is that if you have to remove the engine to do something, then while the engine is out and the head off, then you change it.

So in this case I'd be doing the base gasket and if it hasn't been done before, the front rubber cam chain guide too.

 

[Bob Wegman]

I have used the Athena green gaskets on a number of XS650s with no problem. What are the issues for uninformed me?

 

[Jim]

Conversation starts at about #2355 and goes for a few pages.

https://www.xs650.com/threads/jims-1980-sg-miss-september.50545/post-734265

 

[garyr]

If you don't break the "seal" (allow the cylinders to lift off the block), then I don't think you need to replace the base gasket.

With the valve not closing all the way, that may indicate it's bent. To determine if it is, chuck it up in a cordless drill and spin it. If it's bent, it will be quite obvious (it will "wobble" all around, lol).

Thank you 5 twins, what I thought but wasn't sure. Bike was running perfectly for years. .....pulling the engine out now. It was a hot day and went to a bike show, so idling around, then used aviation fuel on the way home, ran fine. Next time I started I had the issues. I think the Guide is galled. The bike has always be susceptible to hot days. Before the 750 kit once shut off in traffic, it over heated but was fine.

I had back in the day Huges build the engine and I had issues with Mikes parts. (he did a great job, but doesn't work on them anymore). I had stainless valves break, who know how good the guides are. I hope he put oem back in bought doubt it.

I have a 78 GS 1000 and when that head comes off you have to replace the base gasket or it will leak. I've never had a XS engine apart but it looks basic...I hope.

Thanks for all the help, any tips will also help.

 

[garyr]

Also any tips on getting the engine out with one person. I have a bike lift and a bunch of scissor jacks. I was going to put a scissor jack under the engine, jack it up slightly over the frame and lift it out myself. I think the engine is about 150 pounds. I don't have room to lay the bike over.

I have a lot of manuals and cant find a paper I had on the sequence and torque on the engine mounting bolts.

Its been a while since I posted, I'll try and take some pics if I can remember how to.

 

[Jan_P]

Also any tips on getting the engine out with one person. I have a bike lift and a bunch of scissor jacks. I was going to put a scissor jack under the engine, jack it up slightly over the frame and lift it out myself. I think the engine is about 150 pounds. I don't have room to lay the bike over.

I have a lot of manuals and cant find a paper I had on the sequence and torque on the engine mounting bolts.

Its been a while since I posted, I'll try and take some pics if I can remember how to.

Getting the engine out
Machine on center stand
I nail together a stool by 2 x 4 inch planks the height of the frame lower tubes
Then with the chest against the upper frame tubes
One gets good force to lean and lift motor out step by step and there is plenty of points to grab it
Can put some protection if you like on the frame

 

[garyr]

Almost ready to remove the engine......figured I would pull the starter to make it easier. What a mistake, I forgot that held the crankcase oil in, what a mess. I haven't worked on this bike in a very long time.

 

[GLJ]

Since you've drained the oil remove the drain plug from the sump. That will give you another 1/2 inch or so of clearance.

 

[garyr]

Well the tough hurdle for me is over, I got the engine out by myself. If you use a scissor jack and a piece of wood you can remove the engine bolts and let it rest on the jack, then push the top of the engine forward so the exhaust studs almost touch the frame, then jack the engine as high as you can to the top cylinder doesn't hit the frame. Then the engine is free. I was able to waddle or rock the engine around, almost to heavy for one person. I did remove the starter, make sure you drain the oil first.

Now the fun begins and get the head off.

 

[garyr]

5twins...you were right, I have a bent valve. It looks like the exhaust valve hit the piston? I thought this was a none interference engine. I don't know why but for some reason the valve must have stuck.

Sending out machine shop, new guide, valve spring and keepers.

 

[willis]

Are you replacing the piston or going to run it as is?

 

[garyr]

as is. its nothing

 

[zrx1100]

maybe smooth out this area bit so that the valve does not catch?

 

[Jim]

as is. its nothing

You had a (cast) aluminum piston contact a steel valve hard enough to bend the valve.
Just me, but I wouldn't trust it.