Engine rebuild....is it worth it?

[SD_GS500E]

So I've had this bike for about a year now, and it's become my daily driver.

It seems to drive OK, but I recently developed a vibe.  After searching, most people seemed to point to carb sync as the cure.  got a manometer and figured I'd try. 

Well, I read way too much before I do any job and saw enough posts saying if your valves weren't adjusted, you were wasting your time with the carb sync.  So I read too much about valve adjustment.  I must have spent well over 10 hours reading articles, posts, wikis, watching youtube (BaltimoreGS...your videos rock!)  The hardest part of the job was waiting for the valve shims to show up. 

One valve needed one 0.05 shim, two valves went down 0.10.  But now, both intake are between 0.05-0.06 mm, and both exhaust are 0.08-0.09mm, which from what I read, it's ok for the exhaust valves to be a hair over.

Then I did a compression test because I'd seen oil burning before the adjustment and noticed my oil got pretty low.  (and can someone tell me definitively, should I check the oil with the oil cap resting on top or totally screwed in?...I found people telling me both ways).  Anyway, both cylinders measured out at 105psi.  The manual said 142-199 with a 114 minimum (or 112, I forgot).  I was going to check again after it ran a bit so it was fully oiled as it had been sitting for a week or so with no valve cover while I waited for shims to arrive.

Anywho, if it were my Jeep, I'd rebuild it.  But I see a log of folks say just buy a new engine.  How much does a new engine cost?  And where do you get one?  If it's just a rebuild, I don't see the difference in doing the labor yourself or paying someone else to screw in some bolts.  Of course the head and block would go to a machine shop for the valve job and the honing/new pistons.  But other than that, I tend to trust my own work more than others.

So I was looking for input.  Is it better to rebuild, buy a new engine, buy a used engine and hope for the best, drive it into the ground and look for something newer?

[RossLH]

It's probably best to just replace the engine. Buy a used one from ebay or craigslist.

[Badot]

Oil gets checked setting the dipstick in without screwing it in.

If you're happy with how the bike runs and aren't getting gas in the oil, don't worry about the compression if that's your only problem.

[fetor56]

"I tend to trust my own work more than others"........SOUND philosophy. 
As already said.....oil cap resting on top.

[SD_GS500E]

Yeah, so, uh....apparently holding the throttle open is important on a bike during a compression test, huh?

compression went from 105 to 150, and that was cold....now I understand why it didn't feel that bad.

But, just because I'm a tinkerer type, how much is the common cost of a valve job and cylinder bore on a bike? 

I guess the better question would be, just how hard is a valve job and how much is the common cost for a cylinder bore on a bike?

I'm no pro mechanic, but I was a machinist for 5 years making aerospace component parts and I've been fixing and rebuilding Jeep 4.0 engines for a while, so I'm used to working with fine tolerances and combustion engines....and I drink beer, so that helps!

[RossLH]

Valve jobs are cheap. Do it yourself. What makes you want to mess with the cylinder bore?

[SD_GS500E]

just to clean up the cylinder wall and rescore it. 

It's not something in my immediate future, since I realized my "Oops!" with the compression test, but it is still in the lower end of the accepted limits.  And being that it is visibly burning oil, it's likely the rings are on the way out.  And I figure if I'm going through the effort of doing rings, it would make sense to get new pistons, clean up the cylinders, get a valve job, and be done with it for a while.

[RossLH]

150psi is plenty of compression. How quickly is the engine consuming oil? It's not unusual for GS500's to burn oil. Unless it's an obnoxious amount, I'd just keep it topped off and not give it another thought.

[Joolstacho]

It'll just be top end won't it? Pretty easy, not too costly if you're doing it yourself surely.
If guides and seats are a problem that'd push up the cost obviously, but chances are it might just need valves, rings and a hone.
Ebay or Craiglist engine? ... you might get anything, I doubt if you'll find one with guaranteed oil pressure, or do you know something I don't?
The one you buy might be a lot worse than yours.

[The Buddha]

Yes Jools - top end, and top end is easy cheap and quite doable for the shadetree mech ...
Cool.
Buddha.

[bmf]

Was just going to say "open the throttle" but you got there first:). Did a new valve job with new valve stem seals etc.- was about 100$ but the two gaskets come to about 70$ on top, remember that new cylinder hone means you have to run the bike in again for 1000 miles, and you must use new rings if you hone - another 70 bucks, unless you break one (like someone who shall remain nameless) in which case it is 100 .

150 psi is good, I would not touch it! You will drop dirt in the crank when you lift the cylinders (captive inside the cylinder stud holes) which can force a lower end rebuild clean out (as happened to someone who will remain nameless)

[Funderb]

burning oil could just as easily be valve seals and/or guides as it could be rings. 150psi says probably not rings.

As for a total rebuild, yeah, i did one for less than 100 dollars. That cost way less than a $500 engine plus shipping.
Bike was down for as long as it took for the rings to arrive (plenty of time to run a honer through the jugs..) The only other thing i did was to scrub some carbon off the pistons and head.


Then I balanced the carbs. It was great. I maintain, with even my (relative) limited experience with this engine: unless you destroy the bottom end/tranny or the head is catastrophically damaged, its still a perfectly good engine.

[Joolstacho]

Obviously take care not to get crap into the crankcase if you're pulling the barrels, but I wouldn't panic about getting stuff down there. One of the good things about this motor is that there's a nice big sump cover that you can remove, (and remove the gauze filter too), then you can pour Kerosine down to flush out any debris. Easy. I used about 2 litres, I'm pretty confident it's clean down there now.

[SD_GS500E]

So I've been busy with work and just got back to this thread.

Thanks for all the responses!

So am I getting it straight, on a bike engine you don't need to take the block in to a machine shop or buy new pistons?  You just run a honing tool through it and re-ring the existing pisons and do a valve job?

I guess I'm used to a jeep engines where you just drop off the block with a new piston kit that's .020-.030 over and a machine shop will bore it, clean it up, and install the rings and pistons.  Figured I'd have to do the same with the bike.  At the same time, I generally drop of the disassembled head for a valve job that generally replaces springs and caps and grinds the valves as well as checking the valves themselves and the valve guides.

[yamahonkawazuki]

Obviously take care not to get crap into the crankcase if you're pulling the barrels, but I wouldn't panic about getting stuff down there. One of the good things about this motor is that there's a nice big sump cover that you can remove, (and remove the gauze filter too), then you can pour Kerosine down to flush out any debris. Easy. I used about 2 litres, I'm pretty confident it's clean down there now.

plastic bags work to keepstuff out of engine innards. just have to remember to remove it lol

[ohgood]

Yeah, so, uh....apparently holding the throttle open is important on a bike during a compression test, huh?

compression went from 105 to 150, and that was cold....now I understand why it didn't feel that bad.

But, just because I'm a tinkerer type, how much is the common cost of a valve job and cylinder bore on a bike? 

I guess the better question would be, just how hard is a valve job and how much is the common cost for a cylinder bore on a bike?

I'm no pro mechanic, but I was a machinist for 5 years making aerospace component parts and I've been fixing and rebuilding Jeep 4.0 engines for a while, so I'm used to working with fine tolerances and combustion engines....and I drink beer, so that helps!

150 psi is a happy engine, I wouldn't mess with it till smoked like a two stroke, or wouldn't run anymore.

Shimming the valves is a good idea if they're getting tight, otherwise just toss more plugs on and see if that helps.