Cylinder Head Replacement Help Needed

Hey All, I am relatively new to the forum, and in the process of replacing the cylinder head on my 82 650 Maxim. The reason I am replacing it is that I sheared of the intake manifold bolts, and bolt extractors in the head that was on the bike. Having read the forums, now I know better, and would also advise against taking off the intake manifolds unless you really need to.

I recently purchased a cylinder head from a member who was parting a bike that had 8k miles. I just got around to installing it after receiving it a month ago. I have a couple questions:

1. I and wanted to know how clean do the surfaces against the gasket need to be from the old gasket (absolutely zero residue?)? I have been cleaning it with degreaser, and I've gotten it close but not spotless. The Hayes manual does not specify. I'm not sure how muc the spray adhesive will help with the surface where old residue is not completely removed.

2. I also just took a close look at the new head for the first time, and noticed that it has some significant gouging and marking on it. I am concerned that this gouging and marking might cause leaks. Below are some pictures. I was hoping to get the opinions of some of the more experienced members.

 

Yes I'd say the damage to the head has potential to cause a couple of issues, not least the flake on the camchain tunnel that looks like it's about to break off & potentially drop into the engine. I'm not sure what's happened to the head for it to be knocked about & dinged up like that but personally speaking I'd take it to a machine shop to get their opinion & maybe have a small skim taken off if it'll stand it (unsure of specs for this head, but just enough to clear the worst of the gouges).

That way you negate the question of cleaning the old gasket off too, but normally I'd clean an aluminium head with solvent and a plastic scraper, or very carefully with a Stanley knife blade. I'd clean the block/jugs with solvent & blade, you're aiming to get all the old material off. Usually there will be a "shadow" of the old gasket left but you don't want any actual material remaining at all.

EDIT-: just a small issue, I see the code 5G2 on the head. That would make it a 750 head surely?

 

Maybe you could take the new head in to be resurfaced?

 

I was told that he head is from an 82 XJ650 as well. I should have taken a closer look when I received it. Is there a way to confirm if the marking means it is in fact a 750? Does anyone have an idea for the cost to get it resurfaced by a machine shop? How much material can they take off before it is outside of tolerance?

Edit: Also, if I placed black RTV around the camchain tunnel gouges, would that hold up, or am I just opening myself up to head gasket leaks, and future problems?

 

It could still be, Yamaha could have used the same head castings but I just know the 5G2 code relates to '81 750RH (5G200) & '82 750RJ (5G210).

I believe yours would be a 5N8. Don't you have the old head to compare? that would be a great help until someone can confirm if this is the right head.

 

I do have the old head. I will double check it once I get home tonight. Thanks!

Edit: I just found this thread from Chacal. Looks like the heads had the same part #. http://xjbikes.com/Forums/viewtopic/t=3 ... rt=30.html

 

I know you mentioned the replacement head only has 8000 miles on it (correct?) but since you've got it off it may be worth replacing the valve stem seals as well as doing a valve job. That's the fun stuff

 

Thanks Moeller. Since I have it off, I am planning on doing that as well. Right now, I just need to decide if I can go forward with that head, or if I should just start over and purchase a different one.

 

Ahh right that's good at least, pending double checking your old one, we have the correct head to work with

I would say you might as well persevere with this one since any head you buy is 31 years old now nearly 32 so will likely need/benefit from the stem seals being changed as moellear said & the valves being lapped in nicely. And since this one is low mileage there's less chance of mechanical wear to guides etc

First port of call is to a decent machine shop to get the head gasket surface looked over & sorted. I'm not sure how much they would charge to skim it but get at least 3 different quotes/opinions if you can. It may even only need a going over with a surface plate/compound depending on the actual depth of gouges & any warpage.

You can change the stem seals, check valve guides/springs are in spec & lap in the valves yourself really easily with a valve spring compressor & a lapping tool (wooden stick with a suction cup on the end, more or less) and compound.

 

top picture, that's bad. second pic, that's a oil leak. third pic, that's clean enough.
that has to be milled, the good side is you still have your original head.
i would think your original will be cheaper to get the broken studs out than to get that one milled.
don't want to start a big stink but i sure don't want to buy anything important off of whoever sold you that head, just say'en
if your feeling frisky, search youtube for "resurface head"

 

Before I purchased the new head, I took the old one into a machine shop, and they said it was too far gone to repair. That was 100% my fault for not checking the forums before trying to extract the bolts myself.

At this point, I want to get my bike running, and correctly repaired so I can dig out of this hole, and move on to the next project!

Thanks for all your guys' help. I will take the 'new' head into a machine shop, and see what they can do. Depending on that, I may or may not purchase another one via Ebay.

 

Janico, Not a problem for not having checked the forums first. If you HAD, you would have left the boots on, you're engine would develop a leak on top, the cyl gasket would have blown through, and the piece of metal in the cam chain tunnel would have fallen in............you're lucky you didn't know what you were doing and took it apart. LOL

The hard part is done. Now, all you have to do is get a replacement head on there and button it back up.

Look on the front of the head. There's a little rectangular casting that will have a number like: 648, 753, or something like those......(can't remember the correct ones) but if it says 6--, you have a 650 head. If it says 7-- you have a 750 head.

I you have a 750 head on there, make sure that you have the right jets in the carbs to go along with that............

Dave F

 

I'd take that head back & get a refund.

 

+1.

Too much material would need to be removed to repair the one big gouge. To fix it properly it would need to be welded in and then the head resurfaced. That would probably cost significantly more than what you paid for it.