Pulled the Heads on a '82 XJ650

Hello XJ Fam. My first post in the forum, you will probably see me poking around and asking questions as I'm doing a full rebuild of a '82 XJ 650.

To be honest, this is my first full engine rebuild. I was seeing compression from 2,3,4 cylinders at around 90, and cylinder 1 was at 60. I dropped some oil in cylinder 1 and that brought the compression up to 90 like the others. Thinking this was a piston ring issue in cylinder 1 (and the motor has 35,000 miles on it) I decided it needed a full refurb.

I pulled the heads/barrels off the block today and this is what it looks like:





So a couple of questions if y'all can help a rookie out.

1) I wasn't expecting to see the studs on the exhaust side so corroded. Is that what they usually look like?

2) There were also some type of deteriorated stud sleeves on the exhaust side studs, is that also normal?

3) On visual inspection, the piston rings looked to be in good shape on Cylinder 1, making me think the low compression was from something else. I'm not quite sure where to go next on this, other than to assume if I replace all the standard engine rebuild parts and head gasket that the compression issue will be resolved.

4) Does anyone see anything else in these photos that I should be paying attention to that is out of the norm for these motors?

Thanks in advance for any suggestions.

-Mind The Tread

 

Have a look at the valves. Do they seat nicely in #1?

 

Welcome to the forum. How long have you have the bike? Do you have a Haynes manual for it? 35,000 miles is nothing for one of these engines. You probably have stuck piston rings which can be freed up with a 50/50 mix of acetone and automatic transmission fluid.

The studs are corroded because they are visible through the fins on the exhaust side of the engine. Yamaha fitted the sleeve during manufacture to protect the studs from the elements. The sleeves deteriorate all that is normal. You should clean up all that loose debris around the studs, some of it will have got into the crankcase already.

 

Did you happen to check the valve clearance before you tore that down?

 

Yes it's a good check to make and use the freeing up piston ring mixture before dismantling the motor.

 

We will walk you through this, but you jumped right into a big job before trying all of the easy things to get the compression back up.
Was the engine running at all before the teardown?

The XJ engine typically goes 100,000 miles or a bit more before needing a rebuild, but that does depend on prior owners taking care of the thing.

Things that can cause low compression:

Valve clearances need adjusted (as mentoned)
Stuck piston rings (as mentioned)
Corrosion on the cylinder wall from stitting (usually remedied by running the engine as you would to seat new piston rings, but not always).
An improperly calibrated compresion gauge (we've been seeing a lot of this from the inexpensive compression gauges that most auto parts stores sell).

But now that you have it apart you should get or rent a set of cylinder bore gauges so you can measure the bores to see if anything needs to be done other than a light honing and new standard sized rings.



When it comes time to order parts get them from @chacal info@xj4ever.com
He has the correct parts and backs his sales with real customer service. He also has the knowledge to make sure that you get everything that's needed for the job at hand, like the special washers for the head that your local Yamaha dealer has to order from Japan and somehow always seem to be on backorder.

 

Thanks all for the replies y'all! Super helpful.

The engine never ran, no idea how long it sat (years). Previous owner gave me the carbs in pieces and had rags stuck in the carb intakes so I bought this baby with the intent of doing my first full engine rebuild.

Thanks for the connection with @chacal, I'll get with him to get a list together for a parts order!

Interesting call out on calibration of the compression gauge, something to look into for sure.

I'm sure I'll be around with more questions as I go! This forum is a trove of info, going to take me a week just to dig into the knowledge that has been shared.

-Mind the Tread

 

“Clean up the loose debris around the studs” indeed, to blooming late I would say...

 

If you really want to do the deed , the valves should be lapped and the valve seals replaced since the head is off. If you split the case get a repair kit for the starter clutch replace the springs and rollers. Replace the chain guide as K Moe stated xj4ever will have the needed parts . The worst part will be inspecting the crank and figuring out bearing measurements, a good machine shop will be able to polish the crank journals and , give you measurements. On You Tube see Mezmos xj650 does a full rebuild really good video series. Cheers