Low compression Cyl 1 & 4, high valve clearance...?

Hi Y'all,

Already been perusing the forums and have found a lot of useful info; thanks!

I recently picked up a 1982 midnight maxim xj650. Decent looking bike that I am hoping to build out into something custom. The fella I bought it from told me it had good compression, I think he was mistaken or I am missing something. Below I outline what I've done to test compression and what the problem I am experiencing is in hopes someone has some ideas....

Tested compression across all cylinders, twice (granted I cannot get the throttle wide open, because it's stuck, but wanted to test for consistent numbers across cylinders. all plugs out, etc...)
Cylinder 1: 29
Cylinder 2: 119
Cylinder 3: 129
Cylinder 4: 25

I am really curious why the two outside cylinders are so much lower than 2 & 3.
I've checked valve clearance thinking they might be tight, but they are actually loose - significantly looser than spec.

Should I try to pour some oil into the cylinder? If so, do I just do that thru the plug hole?
Does this sound like a piston ring issue; possible stuck? Should I try the various techniques for freeing up the rings?

...I am a noob to this so sorry if these are stupid stupid question. I really appreciate any and all advice and/or thoughts.

Steve

 

remove the carbs if you have to to do the test
did you remove the air filter?
is the throttle stuck because of the cable or will not turn at the carbs?
table spoon of oil in the spark plug hole. its gonna spray out if the hole isnt pluged so cover holes not in use
there is some debate on cold or warm engine results

post your valve clearances if too loose your not going to get air in to compress

atf and acetone mixture will free up the rings 1part atf and 1 part acetone, let it soak. untill atf mixture is gone at least overnight

did you check your oil level? do you know how?

 

remove the carbs and air filter to do the compression test? Is this a work around for the throttle issue? OK. I can try that.
I did not remover the air filter - but that shouldn't effect two cylinders and not the other two... right?
throttle was stuck when I got it the other day: won't turn at the handle, I can manually open the carbs with a small screwdriver.

I'll try the oil today or tomorrow.
Ain't going to get a warm engine start here....

I will post valve clearances after I re-measure them later today.
But for cylinders 1 & 4 the intake was nearly twice spec, maybe a little more and the exhaust was a little looser too. Cylinder 2 & 3 was closer to spec, but not perfect and tighter.

 

your first step is to check and correct the valve clearences. you are asking and answering the question
read this link it will tell you a lot of things

The Information Overload Hour

then go to this link
http://www.xjbikes.com/forums/forums/xj4ever-supporting-vendor.23/

and read all the links starting with and after this one the links above this link is where you get all your parts
TECH TOPIC: The History of Yamaha

 

A shot of oil into the cylinders increased compression significantly
all within a few PSI and hovering around 120.

Will double check valve clearances
thnks

 

Double checking valve clearances is never a bad idea, but increased compression after adding oil is a good sign of stuck rings or worn rings/damaged cylinder walls and will not increase compression if there is a valve issue. The good news is you saw a significant increase and they are close in readings.

 

I guess the other glass half full of all this is that I planned to strip her to the frame anyhow: motor was pulled this afternoon/evening and will live at my buddy's house for a while, who has the requisite tools to check rings, etc...

 

unless your in it no matter the cost your best bet is to confirm motor 1st before spending money on cosmetics, and frame related items

 

Oh yeah, for sure: no sense in spending dough on frame related / cosmetics if the motor is completely shot.
I don't however, think the motor is completely shot: 12k original miles and the compression came back pretty solid with some oil.
Going to check rings and pistons and go from there.
thanks

 

Drop equal parts acetone and ATF down the spark plug holes and let it sit for a few days. Spin the engine by hand and repeat. After a few cycles of this process, recheck compression. IF compression increases then you just had stuck rings and can skip tearing the engine down.

 

OK. The motor is already pulled off, but I hadn't planned on tearing it apart for a few weeks, will try the ATF+Acetone technique and report back.
Hopefully I will be able to figure out all the electrics as my markers didn't stick...
I am sure it will be fine...
not looking to ride her tomorrow.

 

You have available Wiring diagrams at your fingertips (literally) get your motor straight first. and as Kmoe said turn it by hand not starter.. Really Important at this stage.