New XJ650 Maxim Owner, Cylinder head cracked

Just bought my first bike a couple days ago and it's a 81 XJ650 Maxim. Sat on a porch or shed for a few years. Cylinder head is cracked, probably from a few Vermont winters. Waiting on a replacement cylinder head from ebay. Any tips for replacement? Any other things I should look out for?

 

Buy a service manual. It will have all the information you will need to replace the head. Be careful when you install so you don't bend the valves by setting the cams up wrong.

MN

 

Buy a service manual. It will have all the information you will need to replace the head. Be careful when you install so you don't bend the valves by setting the cams up wrong.

MN

 

Did you make sure it's the CORRECT cylinder head? Not all 650 Maxims had the same motor, and eBay sellers tend to "fudge" interchangeability.

1980~'81 650s Maxims had non-YICS motors (like yours in the pic) but the '82~'83 650s had YICS motors. The cylinder heads are not interchangeable.

 

Probably be a good idea to get a new valve cover gasket & donuts as well as a head gasket. Get em right here from our man Chacal @ XJ4ever at the top of the page. Good luck resurrecting your Max.

 

Nice grab! Good luck with the build.

That seat is freakin' awesome... A level of rediculousness I haven't seen in a while!

 

It's a pre-YICS motor. No donuts. Just a flat "composite" gasket, "normal" screws, and separate rubber "half-moons" on the RH end.

But by all means, XJ4Ever IS the man for parts; and new gaskets will be needed anytime you crack a cover that hasn't been touched in 30 years.

 

Where is the head cracked? Post a pic

 

Thanks for all the responses and info! Greatly appreciated! The cylinder head I ordered is off an '80 XJ650. Will definitely order the gaskets asap.
I'll post a pic of the crack when I get a chance tomorrow.
Can't wait to really dig into this project!

 

Before you go ripping into that engine. Get a good compression test to make sure the rings are still in good shape. Otherwise you can figure in the extra $$ to put a fresh set of rings in it while you have the engine apart.

Other gaskets/seals you will need:
Intake boot to head. Get new bolts also!
Exhaust

Ghost

 

Nice seat! I have two or three of those, but the big problem with them is that WHEN they start dry-rotting and cracking, you can't just peel to cover off and install a new one. That cover is sort-of molded to the foam, and it's a real pain to replace.............plus there are no nos,oem, or aftermarket covers available that I know of...................yet.

dave f

 

I highly doubt it was cracked from a winter condition. If that was the case, we'd be screwed up here in the north Now... if the engine was full of water when it froze, then i could see it cracking

 

Finally found the time to post a pic...

 

yeah, that could be a problem. Looks like it could be indicative of some other major issues, too. However, if the damage is limited to the head, then yeah, replacing the head will solve a lot of things.

Be aware.....if you replace the head, you'll want to try to get a whole head assembly with the cams, that way the cams are already mated to the cam seats and carriers. Heck, while you're in that far, pull the cylinders, hone them, check the ring gaps, put new gaskets in, and before you put the head on, lap the valves, install new stem seals, do the valve shims, and you'll have a nice new top half to the engine.

Keep us posted....

Dave f

 

There is definetly something wrong with the lifter bucket/shim on that cylinder. Looks like the shim came loose and the cam pushed it into the head cracking it. Never seen that before.
Replacing the head is the only way to fix it.

 

Wow, never saw that one before either. I am most curious what the cam looks like too. If it is the shim that caused it, I wonder if it was a situation of the shim/valve had never been checked, and kept pounding itself into the head, or as mlew stated, maybe po checked valves, but put in a wrong shim making it really loose.

Jammin, when you start tearing it apart, can you post some pics of the cam and bucket area?

Also, +1 on others advise to check compression before you take it apart. It is an opportune time to freshen up the rings and cylinder bores anytime major work is done. If you have already taken it apart, go ahead and remove the cylinder block and have the bores mice'd.

 

Thanks for all the advice! I'm currently ordering parts and looking for resources to tear it down soon. I've considered ordering a compression tester but might just ask around for one.
I'll be taking plenty of pics so I'll be posting them here. I'm really interested to see what happened to it.

 

You can go to a parts store and do the loan-a-tool thing on the compression gauge.

 

So I've finally tested the compression. Cold dry compression was as follows for each cylinder. 1-100psi, 2-91psi, 3-75psi, 4-75psi
Now I just changed the oil on it before I did this and I didn't run the bike before the test.
Just let it turn over for a bit. I also did a wet test and the values were: 1-140, 2- 129, 3-149, 4-91.
I'm just wondering if this really is the rings or if it has something to do with the head being cracked.
If it is the rings where do I get the original size rings?

 

Honestly? if you suspect its the rings try to find a whole engine with better compression. Piston rings are expensive, especially original sized.

I would lean towards the fact that you have a cracked head which is why the compression numbers are low. But then again where the cracked location is, is not near the piston compression area so I'm not sure. I'm curious about this situation as well... more experienced folks will chime in

 

With the crack being on the #2 cylinder, and the low compression on The #4 cylinder. The two problems would not be related directly. It is highly possible that valve clearance issues could be the reason for the low compression on #4

With the rise in compression in #2 & #3 showing definate ring problems. You will be looking at doing a complete top end rebuild.

At this point I would pull the head off, and inspect the pistons/cylinders for abnormal/excessive wear. Pay close attention to the #4 cylinder.

As metioned. You may be better off trying to locate another engine. If you find the #4 piston or cylinder beyond service. It would push this more to a necessity.

Ghost

 

I'm pulling the head off tomorrow, but I'm already looking for some engines online. Are there other engines that will fit? Like an 85' xj700, or 750, I'll even go for a 550...

 

the 550 engien will not work as it is a chain drive engine.

All 650/700/750 engines use the same engine case.

The 750 Maxim engine will be a direct replacement with the fact that the 750 engines were only available as YICS engines. This will not cause any problems with an engine swap. Just more of a maintenance, and tune up issue.

The 750 Seca engine will work, but uses solid mounting at the engine mounts. This will transfer a bit more engine vibration to the frame. Once again, only available as a YICS engine.

The 700 Maxim engine will work, but carbs are becoming a problem to locate for these engines. There is a workable replacement with 750 carbs.

another option if you are adventorous,and can collect all the necessary pieces. The 900 seca engine will also bolt in to give a true sleeper for a bike. The problem with this is that the engines are rather hard to get ahold of.

Ghost

 

I got a 900 Engine you can have for $250 Bucks!

No carbs.
No starter.
No cooler.
No Filter Bolt and Dome.

Bring somebody to help you lift it.

(I dont think its a simple bolt-up.)

 

Jammer,

Chacal has a nice write-up on what you need to do to perform various engine swaps.

Dave

 

Thanks everyone! Rick I'll let you know about the 900. For now I'll look for something closer to original. I'll be posting as soon as a have a replacement.

 

Haven't been able to find this. Can you point me to this write up?
Thanks!

 

Jammin650,

Welcome. IMO if this is your first bike bring that engine back or swap it out for another 650 non-yics engine and get it running to specs. There is a list of things that need to done before she is road worthy. The first thing you'll need is a compression test and you can't do that without the head being intact. You're on the right track...pull and degrease that head so we can see what's going on with it. Post pics of the head w/o the valve cover. Turn it over and post pics of the valve heads. Post pics of the front and back. Post pics of the block with the piston heads. Hope this helps.

Gary

 

I was going to directly copy it from the page but its too much information at once. Read this Chacal's Information Overload page, about 15% down the page by scrolling. Its titled "Engine Swaps".

 

If you still can't find it, let me know.....I have it as a word doc on one of my discs.

dave F

 

So I took the head off yesterday and took some pics. I didn't have time to degrease it all that well, but most of the oil is gone. One of the bolts was rusted so bad, it held on to the stud...

 

more pics

 

Jammin,

Good pics. I don't know...I think I'm going to let some of the more experienced members chime in on this one. Looks like something was used as as a pry bar and may have cracked that head. Is that head actually cracked through? As far as oil on top of your pistons....Shine a flashlight in each manifold intake boot and see if you see oil on the valve shafts/heads. If so, your stem seals were leaking. If not and FWIW, I'd pull those pistons and see if there are any broken rings. Others will chime in soon.

Gary

 

Hi Jammin, to confirm your fears, yes a shim did come out from under a cam and the proper fix, in my opinion is get a replacement head, they are fairly cheap on Ebay.

 

With that fracture right up against the Valve Bucket Bore, ... you might have a rough time saving the Head with a weld-job.

The Oil fouling of the two Cylinders could be from several sources.
It's severe enough to suspect Rings.
You would have had a clearer picture with a comprehensive Compression Test.

http://www.ebay.com/itm/1981-YAMAHA-XJ6 ... a2&vxp=mtr

http://www.ebay.com/itm/108-1981-YAMAHA ... c1&vxp=mtr

http://www.ebay.com/itm/1981-Yamaha-xj6 ... 2c&vxp=mtr

http://www.ebay.com/sch/i.html?_odkw=Ya ... d&_sacat=0

More: (search Ebay)

Yamaha xj650 Cylinder Head
xj650 cylinder head

 

It's cracked allt he way through... I already have the replacement head, along with a full gasket set. When I get some more time I'll pull the cylinders and pistons. I just hope this project won't drain my wallet as much as I think it will...

 

I did a compression test before I started tearing into it, so that's where the oil came from. The test wasn't good since the reading was better when I poured some oil down the plug holes. I'm almost positive the rings are shot...

 

If it's been stood a long time before you got it, the rings may just be gummed up in the pistons. I can't tell from the pics how bad/good the bores are but if there's no major wear & money's an issue you could clean up the old rings & check the end gaps when they're inserted square in the bore.

That said, if I was going that far with an engine I'd not heard run I'd say better to replace the rings even if the bores only need a de-glaze. I've had good experiences with Wiseco rings, you can order either for the bike if they list it, or from a list of bore sizes & ring thicknesses (I'll try look it up, used it on a '81Suzuki DR400st engine I refreshed few years back as there were no ring sets listed for that)

 

Can't get the exact page to link up with the ring list, but if you follow this link & hit the Additional Accessories tab to the right of the page it gives you a pdf file and about page 4 of that is the rings. Hope that's some help

http://www.wiseco.com/Catalogs/DirtBike.aspx

EDIT-: Sorry, page 5 is where 4 stroke rings start

 

Thanks! When I bought the bike in the fall, it was running. Then I changed the oil this past week and I couldn't get it to start. I'm also looking into a donor engine, but can't find any reasonably priced in good condition.

 

FWIW as you've got a replacement head & gasket set (if I read that right?) and the engine was a runner I'd persist with the lump you have. Then again I'm a masochist anyway, why else would I do the DR? lol

But yeah, if the engine wasn't smoking or making excessive noise then it may be ok with just a glaze-bust on the bores & the old rings (but do check the end gaps are in spec first)


I know the wet test increased pressure, but it looked like a fair bit of oil in there, so maybe it'd also be worth checking the valve clearances aren't closed up on the old head so losing pressure through the valves (lot of oil may have helped seal those too)

 

Okay, that makes me feel a bit better. I do recall there being a faint knock in the engine, but could that have been due to old oil?
I'll probably bring the cylinders to a shop to get them de-glazed. How do I check the end gaps?

 

Hard to diagnose or discount any noise without hearing it personally I'm afraid, but it could have been normal air-cooled engine noise (noticed the "fin ring" dampener rubbers are missing, that'd make things sound louder), possibly camchain not adjusted correctly or at worst could have been rod knock or piston slap from worn bores, but impossible to say with certainty with not hearing it, like I say, could just be normal.

My gut feeling if it was mine would be, if the rest of the motor looks in cared for condition (no scoring in cam journals from dirty old oil, no wear ridges or scoring on bores etc) then pop the barrels off & get a machine shop to put a Micrometer in the bores to see if they're in spec, if there's life in them then have same shop hone the bores (tell them you just want a glaze bust, little as possible taken out of them)

as far as the ring end gaps go, I don't know the spec for them, but you place the rings about halfway in their respective bore & gently square them up by using the piston to push them along, then use the appropriate feeler gauge in the gap.
with any luck the motor won't be as bad as first feared, looking at the head pics the cam journals didn't *appear* scratched or anything so it at least appears to have had regular oil changes. The valve clearances are most prone to neglect on a bike with shims as they take time & money to do them!

P.S. maybe best course of action for the moment is to check the valve clearances on the cracked head, esp 3 & 4. If the clearances are within spec then the low compression is likely to be ring related, but I hold out hope that the exhaust clearances will be non-existent :wink:

 

Thanks bloke! Checking the clearances will be the first thing I'll do. Keep your fingers crossed. Got a good remedy against carbon deposits?

 

No worries, if you can get a couple of closer photos of the bores I'd quite like seeing what they look like, ideally at an angle so you can see the wall of the bore at the front or back. Just as a general hint as to what she's like down there.

Fingers crossed them valves are tighter than a nun's chuff hey!!!

carbon deposits on aluminium, brake cleaner & brass wire brush always does me proud (it works out cheaper over here if you get a gallon of it instead of the aerosol sprays, but I find the spray stuff is great for blasting crud away from where you don't want it) and it evaporates completely too with no residue. Plus it's the best degreaser ever... 8)

EDIT-: I'd better hit the hay, it's 3.10am here, got a busy day tomorrow testing my rebuilt carbs & shopping for brake lines & tyres n stuff! 8O

 

I won't be back to the bike till a few weeks from now, as I'm back at college, but I'll post pics then.
Thanks again! Have fun with the new toy!

 

pull the jugs, don't remove the pistons yet, post pics, let's see what we have.

Gary

 

This project is going to set you back a few bucks, ... for sure.

 

I've been considering getting something else for now and putting this one on the back burner...

 

That would be the thing to do if you just want to ride, that way you won't be tempted to rush & can buy the parts you need over a few months. Rushing is the father of all cock-ups (I was rushing when I went to the shop today, got my fuel lines & bits but completely forgot plugs, and sod's law, they've fouled up like a gooden after a few seconds running & now the shops shut )