Awesome. Low Compression on all 4.

Well..... I was about all set to get my valve shim work started, and a friend stopped by with a new compression tester. Its a Harbor Freight model, so I was a little weary of it, but I thought it would be nice to put some numbers on what has only been a finger to this point. What I thought was a good shot of air out of the plug socket apparently wasnt. When I hooked the gauge up I got a reading of 75 across the board. With a dab of oil those readings jump to 125.

The bike sat for the better part of 6 years. The first thing I did was the finger compression test, and I thought everything felt okay. So, the carbs were cleaned, fluids drained and filled, and valves were set to be checked, when this popped up. I managed to get it started hasnt been ran other than some random idling trying to get everything sorted out.

I suppose at a bare minimum rings? Pistons? Motors Junk?

I suppose there is the possibility that the Harbor Freight gauge is bad? Would a tsp. of oil in the cylinders make the compression jump regardless? Or is this not looking good?

After digging through the manual Im just gonna go ahead and check valve clearances anyways. Apparently tight clearances can cause low compression.


-Kaya

 

The combustion chamber is 23 CC's which sounds small, so if you added 12 cc's, you would effectively double your compression, less the amount absorbed into the ring-pak.

How about trying your compression tester on a car engine that runs good, and see what it says.

FYI - a motor wont usually run at 75 PSI.

 

Tested it on the trooper. Its a working gauge. Sits right at 75. With or without WOT, and with or without carbs.

The bike would fire right now if I went to start it. Im gonna pull the valve cover and check clearances still, but would I show equal low compression all across the board if it were just the valves clearances? Wouldnt it be uneven compression?

Im hoping it could still be the valve clearance, but at this point, im not gonna get my hopes up.


-Kaya

 

The rings are probably stuck in the lands, through standing, you will have to pull the jugs & carry out the normal tests, if the bores & pistons are in spec, just a hone & fit new standard rings.

 

That sounds more like a glimmer of hope for me. I suppose its time to start pulling the XJ apart.


Thanks guys, Im sure therell be more questions to come.

-Kaya

 

The fact that it's consistent at 75 shows that something is up, as I have the Harbour Freight tester, and I see consistent 147's

To clarify - you have a RUNNING motor at 75 ??

You see - you wouldn't have all 4 rings or valves go bad THAT consistently.

What were your numbers on the "car" engine ??

 

It shows 150psi on the 2001 Isuzu Trooper.

Yeah, the bike runs at 75psi on all 4 cylinders. It doesnt run good, but it starts, and sill stay started with choke. I could even put it in gear and drive it. The consistency is what was odd I though also.

-Kaya

 

Hey guys just you all know a average car compression need to be above 120 - 150 some are higher some a little lower but it stays in that relm.

 

HEED the voice of experience.

The fact that they're so evenly matched even in this condition gives great hope for finding cylinders and pistons in fine condition.

If you keep running it and trying to get it to "fix" itself, then you stand the possibility of hurting something.

Did you at least check the valve clearances?

 

Am doing so now. Just came in to eat, and check for posts.

Ill let you guys know what I find.

-Kaya

 

Exhaust Intake

1 .007" .005"
2 .006" .005"
3 .007" .004"
4 .006" .005"


-Kaya

 

Two tight exhausts and one tight intake. Not out of the ordinary.

And nothing so horribly tight as to wreck your compression, just out of spec.

Gotta pop the jugs off.

And for everyone else reading this (since it's too late for you) this is why a lot of us repeatedly stress the need to do a compression test when buying one of these bikes; so you don't inadvertently buy into a top-end rebuild.

 

Here is something I learned. An Isuzu Trooper should have compression around 190. 40psi more than it read to me. My Trooper runs great so, theres always the possibility that the gauge is reading wrong. Even if the gauge is off by 40 that would still only put me at 125psi if it was still accurate. That might explain why its running.

I didnt buy into this. Ive owned the bike over 10 years. I think ill get a new gauge and try that. If it reads the same, I suppose Ill start tearing the top half apart tomorrow to inspect for issues.


Thanks guys,

Kaya

 

Does our vendor stock rebuild kits?
Anyone know what they run?

Maybe ill get lucky and only have to replace the rings.

Cool...

-Kaya

 

Is there anything chacal doesn't stock?

 

Kaya like you said try a second compression guage. It wouldn't be the first time someone bought one that didn't register properly. Do that before you tear into the top end!

 

Yeah I seriously doubt the gauge. Heres a review of that exact gauge.

"With such a long hose before the check valve the volume of cylinder is gone before it gets up to the gauge. Using it in snowmobile check ups it never gets above 95psi even on rebuilt cylinders. Maybe if the hoses were shorter or the check valve closer to the fitting."


The neck is 24" long.

http://www.harborfreight.com/quick-conn ... 95187.html

It looks to me like I would have to add 20cc of air volume just to make up for the hose.

If the combustion chamber is 23cc and the hose is 20cc....That would almost essentially double my reading?

150psi seems more like what I would want.

The change on my trooper would be much less because of the larger combustion chamber.


-Kaya

 

I have one here that I got from my father in-law and it just fits the bike. I don't think the hose is much more the 6 in. long. It is for a four wheeled vehicle. But I use it.

 

A few cut and pastes from a compression gauge company that HAS a check valve in the spark plug fitting. The gauge in the link I listed does not have a check valve in the fitting.


Q. Hello, I see that people have asked a critical question about chainsaw compression testers. You posted one by a buyer named Jeff. His question, however, was not the right one for the answer he was looking for. The Schrader valve location does not have anything to do with this giving accurate readings on chain saw compression The correct question is: Does this have a check valve inside the spark plug fitting or is the passage inside the spark plug fitting open? I am guessing that your guage has a check valve inside the spark plug fitting as this is where the compression must be trapped to give an accurate reading of the cylinder. If yours has the check valve in this location, I am a buyer as soon as you answer. Thanks

A. The release valve is on the gauge stem, but the check valve is on the spark plug fitting.

"The question from Charles from PA is exactly correct. The volume of the gauge hose can cause huge measurement errors. If your compression gauge is like my automotive gauge with a 1/4" ID hose, 21" long, then the volume of the hose alone will be 17cc. On a 50cc saw with 150psi compression, the gauge will read 112psi. On a 33cc saw, it will read 99psi. I would be a buyer if you could offer a gauge with the check valve in the spark plug fitting, or with tubing of small diameter, eg. 1/16".'


-Kaya

 

Take the Cover off the Air Box.
Remove the Filter
Look-in and around for anything that doesn't belong there.

Leave the Air Filter out.
Lock the Throttles WIDE-OPEN
Test w/ Harbor Freight Tool.
Test w/ s known accurate gauge: Compare.

http://www.sears.com/shc/s/p_10153_1260 ... ockType=G3

 

I just went back and re-read your posts more carefully; I had the impression that we'd confirmed the results.

Go borrow another compression gauge; never rip into a motor without confirming your findings with a second gauge. Or buy a decent one this time; a GOOD gauge only runs between $20~$30.

Most auto parts that loan tools will have a compression gauge.

 

i guess the throttle slides were trained at the factory to know that during a compression they they should climb up out of the way till the test is over or are the slides hooked to the starter switch

 

I actually use threats and bribes to keep my slides in place. :wink: I know how the test is done. I made sure I was doing everything right. Not that its all that advanced though. Im actually starting to have a pretty decent understanding of these CV carbs.

There is no change, whether the throttle is open, the carbs are on or off, or the slides are up or down. 75psi all around.

Thats what the plan is. Its not that I was second guessing you guys, more that I question the gauge. I have just worked on enough cars to know that dead even low compression is odd. It just seems more likely that since my motor CAN run, (not DOES run) and when you concider all the groups of people with bad things to say about the gauge I used, or any long hosed gauges without check valves, for that matter, that the gauge I used was off.

Maybe its all just wishful thinking on my part? I dont know, but after all I learned about compression gauges last night, there was enough information there to make me question the gauge.

You see, my wife runs are Harbor Freight. It has its perks. We get a 20% discount on everything, which is already cheap. Over the years Ive come to expect 1 thing about Harbor Freight. That there quality control measures are non existent. You can buy an item, and have it work great forever..... You can buy the same item on the same day, and it will never work, or die right away.

Hammers are hammers, and pliers work the same whether craftsman or Pittsburgh Steel. (HF brand) I have enough cheap tools to know that some of them work very nicely. BUT, when looking for precision measurement devices....... It may just be better to fork over the extra $20.

Ill let you guys know what I find.


-Kaya

 

Just so Mr Polock, I say pull the diaphragms & slides, leave everything else alone.

 

The process does not require Diaphragm Piston removal.

 

A couple of other things to consider with the test results, are height above sea level & cranking speed.

 

How many miles on this bike?

 

I bought one of those Harbor Freight compression testers a month ago to check out my GS550. Now engine was dead cold mind you, but I read 70 psi across the board. I figured that was good sign that they were similiar. Turned out in the end I had some electrical gremlins causing coil issues, blah, blah, blah. Point is, in my mind it was more important what the cylinders measured against each other, not the PSI on the gauge. It told me to keep looking at other possibilities...and yes, I took the tool back for a refund.

 

Kaya - Did you get a new tester yet? I bought that exact same tester as you and had also read the review that you had quoted. I got an even 90 across the board with the gauge. I am hoping the gauge is bad... and this thread is making me optimistic. I haven't tried it with another, I am curious to know your results.

 

I did, and it was super off.


I shot 150s across the board up from 75psi.


There is no check valve on the fitting that connects to the spark plug hole. That throws compression off.

I wouldnt worry, and I would return that gauge. The gauge itself is fine, just a serious desgin flaw.


-Kaya

 

150s on all 4 is marvelous. That's not a tired motor.

You now know you have a solid starting point; you won't be "wasting" anything you put into the bike going forward.

 

Exactly. It was so depressing to get my first readings. Im heeding you experience now and reshimming the valves. With good numbers I can start dropping money in my front end check over. Then Ill get the carbs squared away, and hopefully be riding shortly after.

I appreciate everything everyone has done. Im not too sure I would ever got my bike back on the road without this site. Ive learned as much in the past month troubleshooting as I have in the entire time Ive owned the bike.


Thanks,

-Kaya

 

Happy to help. You gots a lot more to do, too; it's far from done.

Just think how much you'll have learned once the carbs and brakes are done, probably the clutch, maybe some wheel bearings... plus the front forks will need new seals at some point, etc., everything that corrodes, petrifies, or dries out and crumbles will alert you to its desire to be dealt with.

Patient, careful, meticulous work will pay off in not having to keep going back to fight with things you had hoped were "good enough."

We got your back.

 

IM not all that excited to get on my front end...... I Have little to no resistance on the front suspension as it sits. Its going to be a learning experience for sure. Im not feeling too optimistic about the front end. There is a good deal of oil/grease/something on the fork.

What are your thoughts on using the zip tie method? Im leaning towards the tool instead of the ziptie.

How about locally sourcing carb drain screws?

-Kaya

 

Ahh; you see, owning an old bike is like owning an old house.

The to-do list "re-prioritizes" itself. So you need fork seals now, not later. (That's probably the fork oil that's puked all over the outsides of them.) Forks are easy, there's a how-to on the site (check XJ FAQ Suggestions.) Take the front wheel and fender off and remove the fork legs individually.

Carefully inspect the fork tubes in the area "swept" by the seals (you can do this now, while it's still assembled.) Check for pitting, stone chips, or any other damage in this area that could have caused the seal to fail. In most cases, the seals failed because of age; but if the tube or tubes are damaged it pays to know about it ahead of time so you can source parts.

Did you read both of my valve adjustment articles, including the one explaining the proper use of the tool and the safe alternative to an actual zip-tie? I don't advocate shoving anything down the plug hole myself; the tool has always worked fine for me (once I understood it.)

Carb drain screws aren't just plain screws, so unless the local Yamaha store has them I doubt it.

XJ4Ever has both the originals plus a couple of alternatives.

 

I live my life on older stuff. Not only is it all I can afford, but they come from a time when companies built things the right way.

I did read both your articles on valves. I ordered the tool for the job. It seems more failure free. Hopefully I dont have to tweak the tool to fit properly, but I am prepared to do so if I have to.

I figure Im just breaking the ice with the amount of money Im gonna have to stick into it. The forks look surprisingly clean and defect free, so thats good news. Maybe Ill luck out and just need seals. Pads/shoes and fluid is also needed. Tires needed. Paint needed. Random cosmetics needed. A proper tune, and some new riding gear and Im set. (Rocket gear on a cruiser is not cool.)

Im not too sure my wife will let me tackle my whole list in a quick single order. Or I might be single in quick order.

And so the saga continues.....


-Kaya