Back in the saddle again...

Hello old friends,

I bought a 1982 Maxim 650 in 2009 and spent many hours and dollars getting it running pretty well. This forum and Chacal were invaluable to that process. However in 2013, my job got a lot busier, and I met a girl and sorta fell off the wagon (no fault of hers!)...

The bike (PO installed a 1980 650cc motor) was getting poor fuel economy and reeked of unburnt fuel even though I had rebuilt a spare rack of carbs, adjusted the valves, and balanced/synced the carbs. I did a compression test and my notes say 120 on cylinders 1-2 and 135 on 3-4. I got discouraged, and didn't have time or space to tear into it, and haven't ridden my 650 since then! =(

Well, now, that girl is my wife, and I've got a little bit more spare time, and interest in getting the bike running again. I've got a fresh battery on the way, cleaned out the gas tank, checked all of my electrical connections and am getting ready to do some more work. I just soaked the pistons/rings with ATF through the spark plug holes to help remove any deposits on the rings and will be draining the crankcase, flushing with fresh oil, refilling, then doing another compression test to see where I am at.

I'm OK with the cost of gaskets and rings ($400ish) if that will fix my compression issues, but if the rings look fine, I'm not too excited about spending the extra $1000 or so between machine shop work and new pistons to refresh this motor, plus I'm not experienced at all in rebuilding the bottom end of motors, only the top end (cranks, valvetrain, etc.) ... So it might make more sense for me to try to source a used motor with better compression. Is it realistic to think that new rings will help bring compression back up to spec? The difference between 1/2 & 3/4 is just barely out of spec (14 PSI).

Also, what oil should I be using? Is the Rotella 15W-40 T4 still a good option? Last oil change years ago was with Yamalube, but that is harder to find and not cheap!

Any other guidance on the compression issues?

I'm really looking forward to riding again and getting back into this community. I forgot just how much great info is available here and on xj4ever.com.

Thanks in advance,
Aaron

 

I just found my original thread where you saints were helping me with fuel economy issues. It looks like later compression tests showed lower numbers... 120, 120, 90, 100 - that's very low.

Looks like my first step is to run a new series of compression tests, dry and wet, to see where I'm at. If they are that low again, it goes back to the question - assuming the valves are properly adjusted (I will check this after compression test), could fresh rings fix numbers that low, or am I looking at new pistons most likely (which means a used motor)?

http://www.xjbikes.com/forums/threads/help-me-figure-out-my-crappy-fuel-economy.20773/

 

make sure the tci is for the 1980 nonyics motor.
new rings would fix , before doing thet see if rings are frozen soak the cylinders with a 50/50 mix of acetone for several days it will free up the rings. if your comp does not improve time to tear into motor or replace motor

 

1980 tci 5V2-82305-10-00

1892 tci 5G2-82305-10-00 5v2 10 green label and 5g2 10 red label are the numbers you are looking for

 

Have you checked valve clearance if it is out of adjustment this can also cause low compression .

 

Thanks, I will check out the TCI - but I have to ask, how would that affect compression when doing a compression test? I could see it affecting the combustion and thus fuel economy if the timing isn't correct for the motor...

I assume you mean a 50/50 mix of ATF and acetone... anything special I need to do to flush out the crankcase once that has sat in the cylinders for a couple of days? I just drained the oil but haven't refilled yet. I am guessing most of the liquid will go past the rings and end up in the crankcase. I was less concerned with a small amount of ATF (which I put in yesterday and the cylinders are already pretty dry looking) but I don't want acetone hanging out in my crankcase and clutch area!

Thanks,
Aaron

 

Just checked this afternoon! They are good, I swapped one exhaust valve shim that was a little tight (.14mm), and have a shim on the way for another that is on the low end of clearance (.15-.16) so I can install and see if I can get it closer to spec.

Since no valves had extra clearance, this shouldn't have reduced compression from my understanding of it.

As I did all of this troubleshooting 5+ years ago, I'm happy to run through anything again, so keep the ideas coming!

 

tight valves stay open longer allowing for less compression

the reason to put valves in spec is to eliminate them as the problem


XJ650 and XJ750 air-cooled engines:
Minimum: 128 psi
Standard: 156 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi

your test results
120 on cylinders 1-2 and 135 on 3-4. 15 spread
the problem is not the 15 psi spread it is the 120psi on 1 and 2.

you can just rebuild the cylinders(top end) no need to do the crank (bottom end)
it would be a good idea to consider a valve job while you have the head off if your compression test points in that direction.
compression may improve on its own by running/riding the bike treat 1 and 2 with the acetone/atf mix for a few days to unstick rings or to make sure they are not stuck to pistons
before starting to spend money.


which cylinders did you change the shims?

 

Yes you are right, I was thinking of it backwards... Tight valves would let more fuel/air escape during the compression stroke.

 

added more to above post


Rotella 15W-40 T4 still a good option? yes because it is cheap and easy to find and rated for wet clutches

 

yes but i've seen different kinds of Rotella lately, that's why i stay with Mobil Delvac 1300. it's the only one in a black jug, that way i can send the wife to get it it has a better spout too

 

Thanks for the responses! I was easily able to find Rotella 15W-40 locally for $16/gal (which is cheaper and way more convenient than ordering or making it to the moto dealer) and I verified on the back of the jug that it meets JASO MA/MA2 standards so I felt confident it would work great.

I soaked the pistons/cylinders overnight (put a little fluid in, rotated crank a few times, then topped off with a couple more ounces per cyl) and let the solvent run through the crankcase into a pan - oil filter and drain plug are both removed. I will rotate crankshaft 180* and refill cylinders after work today and let that sit overnight.

Once that's done and I get my valve shim in to loosen up one slightly tight exhaust valve, I'll re-run the compression tests dry and wet. The numbers above are old, and frankly I am not 100% positive I did those with the motor hot, which could have a big impact. So I'd rather just start over and get a baseline for where the motor is at now. I'll report back in a few days with results of the new compression tests.

If the compression comes back decent, I am pretty sure I will replace the rings, as it sure looks to have a lot of oil leaking from the head gasket, and that will need to be remedied if I'm going to be riding it and storing in my garage. Can't stand oil leaks! It seems like if I am opening up the top of the motor to do the head gasket, I might as well do the rings since I'll be right there.

More to come...
Aaron

 

When doing compression test make sure all plugs are out, fully charged battery, and throttle wide open (unless carbs are not installed that is )

 

So mine appears to be an oddball. 4H7-10 black label. It appears this is a 1981 TCI from some quick Googling. Though I don't feel like the ignition has ever been an issue with this bike (with fresh plus and caps).

 

81 what? xj650 and 750 yics motoes all use the same tci

 

chacal post

The 4H7-10 and the 5G2-10 units are almost the same. The 4H7 version does not have the 5th terminal pin to recognize the kickstand relay safety switch circuit.

Paging Dr. Robert, Paging Dr. Robert.........but a partial answer is: no, they are not all the same timing-wise, that's the "other" major difference between the various versions.

http://xjbikes.com/forums/threads/tci-numbers.27545/

in above thread it talks about matching tci to numbers on the pick ups

 

Cool, I can look at the pickup assy when I get home. Both the TCI and the reluctor came on the bike so no clue what the POs did. But if the TCI # doesn't match the reluctor #, and I can get decent compression out of this bike, I'm happy to swap to help it run better. I just googled the 4H7-10 part number and the listings I found all indicated a '81 650, though I don't take that as gospel. It is the internet, after all!

I need to add this into my signature, which I'll do now, but like I mentioned above, the frame is an '82, and the engine number corresponds to a '80. Since ignition hasn't seemed to be an issue in the past I've never investigated whether the TCI is the correct one for the motor, or if it was the stock one from the frame.

I'm also not worried about the kickstand relay safety switch, so if the 4H7 is otherwise correct for a 1980 650 then I'll gladly keep the one I have and put that money to a better cause.

 

in the thread i posted chacal confirms it is for an 81 (no side stand switch he also states something about different timing
so it will start your bike but not run it properly , if it matches your pickups I doubt it was oem on your 82 motor . the 650 had a blend of ycis and non ycis engines going on with the xj650

 

make really sure it's not the valve cover gasket leaking

 

I'm fairly certain the head gasket is at fault, as it appears to be weeping oil... the case is clean above that line and filthy below it. The head gasket hasn't been replaced since I've owned the bike, and I replaced the valve cover gasket shortly after I got the bike and did my first valve adjustment 7-8 years and less than 1000 miles ago (sadly). In removing it this week to check the valves again, it looks fully intact and there is zero oil in that area.

I have only dealt with head gasket failure on water-jacketed blocks, I do not know what the symptoms are on an air-cooled motor - but I would assume possible lowered compression and oil seepage. Is that correct?

 

Well, there are no markings at all stamped into the reluctor, or the plate that the pickups are mounted to, so it seems like a dead end, and I am going to assume that there is no issue here - spark hasn't ever seemed to be an issue. If I am still having power or MPG issues once I get the compression sorted, I will dig deeper into this, but since the only solution would be throwing parts at it (when the existing parts appear to be fully functional), I'm going to hold off for now.

 

unless your compression is ZERO doubt it is a blown head gasket , you can clean up the base and go through the torque settings on the head bolts to ensure it is not loose first , run the engine to full operating temp and then check for leaks . So unless your engine looks like a mosquito fogger while running ( oil leaking into combustion chamber ) or oil leaking like the Exxon Valdez that would be indications of a blown head gasket.

 

OK. Are there any other seals (aside from valve cover) that could fail that would make it appear to be leaking oil right at the head gasket? Once I get this up and running I can clean the entire case and fin assembly with oil eater and then ride a bit and should be able to see fresh oil exactly where it's leaking.

Also the Haynes manual states 23.1 ft-lb on the head nuts - is that correct? Seems super low to me. I checked all mine and they were definitely tighter than that as my torque wrench clicked right away.

 

4

you say your motor is an 82 yics motor you have a tci from something different ,have someone test it in their bike or buy the correct one, mostly to rule out the tci as an issue

 

No, you're reading this wrong... like I mentioned earlier, the frame is an '82, and the engine number corresponds to a '80. So the desired TCI should be from a '80. I believe that the PO installed the TCI from whatever donor bike the motor came from. That seems to hold true, as further reading indicates the 4H7 is 80-81 - this is even listed in chacal's post you linked.

You keep saying the TCI might be an issue - are you talking about my original thread from years ago about fuel economy? Right now (this thead) I am trying to address the compression issue. TCI shouldn't affect compression whatsoever. The fuel economy issue I was having previously is most likely caused by my low compression numbers.

 

ok I understand now but there are 2 types of tci for the 1980 motor

 

mine leaked by the rear stud on #4 cyl, there's a strange looking Oring there.
watch this and skip to 5:33 he points right to it.

 

OK, so after one cylinder soak in ATF and two cylinder soaks in Marvel Mystery Oil over about a week (I heard good things about using this and I felt a little bit better about putting that in the motor than acetone/ATF mix - call me paranoid) I was finally able to get it all back together, add fuel, and fire it up. LOTS of white smoke!!! as it burned off the oil in the cylinders. Had to keep messing with the choke and throttle to keep it running, and it died several times on me. I think the carbs will need readjusted after cleaning out the cylinders, based on my new compression test numbers. Note that these were all done cold because I wasn't able to ride it at all due to rain, and the battery was very low by the time I got all the oil burned out of the cylinders and exhaust. I know you're supposed to do the test hot but I wanted to see how they came back on a cold motor first:

Dry: 135, 115, 120, 135
Wet (a teaspoon or so of motor oil): 150, 130, 135, 155

This seems very promising to me! I would be willing to bet those middle two cylinders would read a little higher once warm. Also all valve clearance have been adjusted and double-checked to amke sure I'm good there. What say you, masters of the motorbike?

My plan is to pull the carbs off, clean and check everything, set them all to factory 'normal' settings, then tune them from there. They were all dialed in for the previous low compression situation to make it run smoothly, but with the current higher compression, I know they will need some tweaks.

Thanks,
Aaron

 

just to post it may help another recent member has an 81 xj650 midnight maxim it has the black label tci on it I have also found one on ebay that is from an 1 xj650 midnight maxim. Not that ebay is a credible source for info but your running issues may the tci is incorrect for your bike.

run the shorty vin from the motor through the vin check to id motor

http://www.dissingermoto.com


this is the id for midnight maxims the first 3 places in your short vin
1981 XJ650 Midnight Maxim USA: 4W5
1981 XJ650 Midnight Maxim Canada: 4W6

 

White smoke = water vapor, oil smoke is blue/black

 

Quick update: I got the bike running well enough to take it for a short ride Friday night (and it happened to be dry for a couple of hours!). Had a pretty solid idle, but still need to tweak mixture settings. One cylinder wasn't firing 100% of the time at idle but once over ~2500 RPM ran great, so there's obviously something wrong with the pilot circuit on that carb. I was too busy with house projects to pull the carbs back off and take them to church, so hopefully I can find some time this week - it's been very wet here, so no rush. Over 5K RPM the bike pulled hard, so I feel like the compression issues are mostly solved, so once I get the carbs cleaned and dialed in I'm just going to ride it and not worry about tearing into the motor.

I now have a healthy amount of respect for Marvel Mystery Oil... And it smells so nice, too!

Thanks for all the assistance and information!

Cheers,
Aaron