should i rebuild my 56k gs 500 motor

[jackinacabin]

My motor runs well but has low compression of 115  and 120 psi. When a teaspoon of oil is added  one side goes to 150  and the other to 125psi... so its not in great shape. the bike is a 1989 but otherwise in good mechanical order and getting tidier as i mess about . From reading and asking on here i think rings and valves are the issues ...  both plugs are about the right colour ... one is slightly  darker but its minimal . the engine makes no bad noises and starts and pulls well ... Its about 300 quid for all the bits to rebuild and if i look about a similar amout for an engine  in the 20 kish miles range ... which way should i jusmp ... ride it til it causes issues , check valve gaps and keep riding ..... get another motor and swap . rebuild mine .... opinions and rationale sought ..... 

[Falken Hawke]

I have a SXV 450 which has a ridiculous maintenance schedule compared to a street bike, especially one like the GS.  It basically will run around 35K miles with routine maintenance every 1500 before something is likely to fail.

With that bike I have a spare engine that is swapped in and the removed engine overhauled and kept until the spare engine is at its limit.  Then the swap and overhaul are repeated.

This is the best of both worlds where I keep the bike going with minimal down time and I am overhauling the engine myself.

Limitations are space for the spare and whether or not one keeps a fully assembled drop-in or just the engine which will use the carburetors and intakes, front sprocket and cover, shift lever or linkage, and clutch release from the bike.  It's not that important to have all of those spares but rather just saves some time when swapping engines.

The other limitation is actually doing the overhaul on the spare engine.  For my SXV, not doing it relatively quickly will leave you with two engines in need of a rebuild.  The GS can fall into that trap as well because "There's plenty of time, I can get to it later".

[jackinacabin]

thanks for the reply , good thoughts ... though as the gs engines run huge mileages if maintained  i will probably never wear a good one out however   I may get a used motor and check and rebuild if needed   so i can take my time  and stay on the road .. ive never rebuilt a gs engine so taking my time is a good idea .. not being able to ride if we get a good day and i am well enough  would be a drag...

[twocool]

Parts to rebuild, at 300 quid, sounds way too cheap to me!  Also will you have to send stuff out for machine shop work?

I checked e-bay (USA) and there's a few "salvage" engines out there...seems like $700 USD is the average price..for around 20,000 miles....some as high as $900...some as low as $300....

It' s a tough call...since with a salvage engine, you take a chance on what you get.

Then you have to think...$700 just for an engine, which might need some attention, when you can get an all-up, good condition, low mileage entire GS500 for $2000 or less...turn key...

What could you sell your ride for as it sits?  Maybe get some cash out of it while it is still running and driving?

But OTOH...the idea of riding what you got 'till it dies seems to make sense...

I've got 54,000 Miles on my '09...no issues (yet)...worth more to me, than what I could sell it for...so I'm gonna run it  until it dies...then junk it!  (I already got my money's worth out of it)


Cookie

thanks for the reply , good thoughts ... though as the gs engines run huge mileages if maintained  i will probably never wear a good one out however   I may get a used motor and check and rebuild if needed   so i can take my time  and stay on the road .. ive never rebuilt a gs engine so taking my time is a good idea .. not being able to ride if we get a good day and i am well enough  would be a drag...

[Joolstacho]

Parts:
gaskets
camchain
tensioner
piston rings
maybe a few valve shims

Sounds as though you're pretty 'handy' so...

Grind in the valves yourself, maybe a few quid to have someone run a hone down the bores.
No need to split the cases.
I realise this is a 'good-case scenario', but all the owner reports is slightly mismatched compression pressures.
Actually I'd do as he suggests, leave it buttoned-up until any sign of trouble occurs.

Go with the LAME theory... leave well alone unless really necessary. More trouble occurs from over-servicing!

[jackinacabin]

Thanks fpr the replies ... my brain hurts with the choices ....  Right now it is running well and this evening after having the carbs out and cleaning them , replacing parts and reinstalling  I feel i would rather slam my balls in door than do a rebuild -- luckilly i have a bad memory and tomorrow I may feel differentely . Its  not so much the difference in compression but the low figures which concern me . The gs should have somewhere abouts 140 psi dry, ideally higher I think ?

  I could rebuild over time and i have a knowledgable friend . I deally just a good motor ... but  its a punt  as  you  say .. i mean my motor sounds fine and runs ok  so even a lower mileage one  could be worn in the same way .... there is a 19k miles one going  from a running bike  but yep tis a punt ....  feeling decidedly lame after swearing  in the shed at the carbs as they refused to shake hands  with the ferklin air box malarky ....

If I do a rebuild it would be a careful job and i would not skimp . If I decide to sell the gs I would very liekly get something with a bit more zoom in it , I  like this  bike  but I wouldnt but  it again  , its fun and it was very very cheap and has got me back into biking  but for  not a lot mor i could have an sv650 or a fazer o r, or , or ....
Thanks all ...  I will keep thinking upon your words

[jackinacabin]

As it sits my fairly tidy for a very early   gs  is probably worth about two packets of smarties and a kit kat as it has a years mot and always starts and runs ... realistically probably its worth 400 or 500 quid max because its on the road and mot`d and has fairings , a higher screen and a luggage rack  and heated grips and the  consumables are all good ....  so selling would not get me far ... other than the low compression the remainder of the machine is now pretty good .... if the motor starts missbehaving i would have to split the kit kat and accept a fun bag or smarties

[twocool]

LOL!  Love it..the  LAME theory (never heard that one that way before!)  Shouldn't it be the LWAURN theory?

Anyway...56K on a motorcycle is pretty good...doesn't owe a dime...

My 10c / mile theroy.....Divide the purchase price by the miles you get before the vehicle dies.....and it should come out 10c a mile or better.    $4,500 motorcycle should give you 45,000 miles!  Putting another $500 or $1000 so into this bike, and it will probably go another 50K miles...beats the 10c /mile by a long shot....!!!

Now figure what happens if you get a three year lease, on a $40,000 car!   Comes out to something like $0.80 a mile, ouch!


Cookie

Go with the LAME theory... leave well alone unless really necessary. More trouble occurs from over-servicing!

[twocool]

Just a dumb question...but I have to ask...

When you do the compression test, do you have the throttle wide open?

Of course, I would never make the mistake of doing the compression test with the throttle closed on my 1984 Honda scooter, and think it had too low compression, and think it needed a rebuild, because it wouldn't go over 30 MPH, but it turned out to be a carburetor problem...

But that "might" have happened to a "friend" of mine!  LOL

Cookie

Thanks fpr the replies ... my brain hurts with the choices ....  Right now it is running well and this evening after having the carbs out and cleaning them , replacing parts and reinstalling  I feel i would rather slam my balls in door than do a rebuild -- luckilly i have a bad memory and tomorrow I may feel differentely . Its  not so much the difference in compression but the low figures which concern me . The gs should have somewhere abouts 140 psi dry, ideally higher I think ?

  I could rebuild over time and i have a knowledgable friend . I deally just a good motor ... but  its a punt  as  you  say .. i mean my motor sounds fine and runs ok  so even a lower mileage one  could be worn in the same way .... there is a 19k miles one going  from a running bike  but yep tis a punt ....  feeling decidedly lame after swearing  in the shed at the carbs as they refused to shake hands  with the ferklin air box malarky ....

If I do a rebuild it would be a careful job and i would not skimp . If I decide to sell the gs I would very liekly get something with a bit more zoom in it , I  like this  bike  but I wouldnt but  it again  , its fun and it was very very cheap and has got me back into biking  but for  not a lot mor i could have an sv650 or a fazer o r, or , or ....
Thanks all ...  I will keep thinking upon your words

[jackinacabin]

 Well , it cost me 450 quid and i have done over 5000 miles on it and it has given me   many giggles ,  i would  chance a guess that it would do another 5000  so its been a good bike  thus far , it cost the price of the ticket to get through the mot and other than cosumables and stuff that i chose to do its been very cheap .  Re the  compression test ... i did do it with the throttle open and also again with a little oil in each cylinder ....

[IdaSuzi]

I guess it comes down to what you want. If you want to keep the bike for a while I would personally run the bike as is for as long as I could and gather parts for the rebuild. I would check the clearance on the valves either way though. My guess is a hone and new rings would be the major need here. But you can't go wrong either by running the bike a while and selling it for 400-500 and putting that towards a cheap sv650 like you mentioned. I guess it depends on how much to want to keep the bike or if you're ready to move on. Good luck!

[Joolstacho]

LOL!  Love it..the  LAME theory (never heard that one that way before!)  Shouldn't it be the LWAURN theory?

Anyway...56K on a motorcycle is pretty good...doesn't owe a dime...

My 10c / mile theroy.....Divide the purchase price by the miles you get before the vehicle dies.....and it should come out 10c a mile or better.    $4,500 motorcycle should give you 45,000 miles!  Putting another $500 or $1000 so into this bike, and it will probably go another 50K miles...beats the 10c /mile by a long shot....!!!

Now figure what happens if you get a three year lease, on a $40,000 car!   Comes out to something like $0.80 a mile, ouch!



Cookie

Go with the LAME theory... leave well alone unless really necessary. More trouble occurs from over-servicing!

I dunno what " LWAURN" stands for,

but here is LAME:
Licenced Aircraft Mechanical Engineers.

Some long time ago, big research study in the aeronautical field found that MORE mechanical problems in aircraft were CAUSED by TOO much stuffing around with them!!!
The conclusion was that less intervention was better than more intervention. We're not saying that stuff doesn't need to be maintained properly, but some authorities got it into their heads that if 'N' maintenance was good, then 'N'x2 must be twice as good.  WRONG!!!

[twocool]

LWAURN = leave well alone unless really necessary...your words!

I've got 38 years in the aircraft world....I know exactly what you are talking about.  Recently attended a seminar on this very subject.

Recent example...My friend has an antique Aeronca Champion ,1946..(I have one too)...his engine had low compression...so he sent it out for rebuilding....came back...now carburetor is all messed up, runs rich...and the crankcase has an oil leak at the center seam...air box no longer fits correctly....the tach stopped working...the carb heat line was installed wrong...as was the oil pressure line....(and a bunch more little things)

We say..."if it ain't broke, don't try to fix it".....same thing.... causes more harm than good...


Cookie

LOL!  Love it..the  LAME theory (never heard that one that way before!)  Shouldn't it be the LWAURN theory?

Anyway...56K on a motorcycle is pretty good...doesn't owe a dime...

My 10c / mile theroy.....Divide the purchase price by the miles you get before the vehicle dies.....and it should come out 10c a mile or better.    $4,500 motorcycle should give you 45,000 miles!  Putting another $500 or $1000 so into this bike, and it will probably go another 50K miles...beats the 10c /mile by a long shot....!!!

Now figure what happens if you get a three year lease, on a $40,000 car!   Comes out to something like $0.80 a mile, ouch!



Cookie

Go with the LAME theory... leave well alone unless really necessary. More trouble occurs from over-servicing!

I dunno what " LWAURN" stands for,

but here is LAME:
Licenced Aircraft Mechanical Engineers.

Some long time ago, big research study in the aeronautical field found that MORE mechanical problems in aircraft were CAUSED by TOO much stuffing around with them!!!
The conclusion was that less intervention was better than more intervention. We're not saying that stuff doesn't need to be maintained properly, but some authorities got it into their heads that if 'N' maintenance was good, then 'N'x2 must be twice as good.  WRONG!!!

[jackinacabin]

Still feeling conflicted about this  but going with the monitor it and keep riding school of thought ... so a valve check and rise on ... just replaced some worn  carb parts and its now as smooth as a smoothy being smooth  , in retrospect it was a bit lumpy bumpy  , flat spots all smoothed and throttle response is now very good ... thanks for the input ... of course if anyone has a super low mileage motor going for peanuts......