Top End Rebuild Preventative Replacement

[dropbear]

I'm planning a top end rebuild soon, but waiting on some parts on back order. The bike is starting and running fine, but it has more than 50,000 km and a compression test shows 100 psi on each cylinder, increasing to 110 with oil. I'm not experienced enough with the GS 500 to know what it's supposed to feel like, but it does seem to have adequate acceleration and will do 110 km/h on the motorway at 6K RPM. However, compared to other bikes I've owned, it feels lacking in torque. That might not be fair though, as these were fairly different bikes and as I've put on some weight since then. Regardless, that compression figure is too low and I don't want problems to develop in the next year or two.

I've bought gaskets, head bolt o-rings/washers and piston pin retaining clips. I've also bought valve seals and springs, thinking they're cheap and that I might as well do those and lap the valves. I've held off buying rings until I open it up and check condition. The bike was sitting in someone's garage for three years and may just need new rings and a ring groove clean.

Anyway here's the question. I have rebuilt engines before, mostly with way more kms than this bike, but I'm not familiar enough with this bike to be sure what service life I can expect from various parts and whether certain parts should be replaced preemptively, even if within spec, while I have the engine open. I'm thinking particularly of things like cam chain and pistons. I'm not going into the bottom end unless I see obvious problems. Thoughts?

[moe_tunes]

I have some thoughts :

    - Before pulling the engine apart check the cam chain for wear in several spots, you measure the distance between 21 pins iirc. That will let you know how much more life it coud have.

    - Cam chain tensioner should be cleaned and checked. New ones aren't too expensive.

    - If you lap the valves you will change the valve clearance so be prepared for new shims - on that note there is a max shim thickness so when you pull the engine apart check to see if any shims are near max thickness. If one or more are, a new valve might be a better option to save hassles in a year or three...

    - Carb intake boots should be checked for cracks and the o-rings replaced.

    - In my humble opinion giving the head a light skim is always a good thing. The GS does have a very conservative compression ratio.

Hope that helps.

[dropbear]

Thanks.

I checked the carb boots/O-rings and measured valve clearances/shims fairly recently when I bought the bike. I'll check other components such as valves and cam chain tensioner for wear when I open it up.

About cam chain, you make a good point. Assessing wear over time/km should indicate how much service life is left, assuming the chain is original. However, although the Haynes manual says the maximum 21 pin length should be 158 mm, I can't find a figure for original length and hence a way of working out actual stretch over the 15 year/50,000 km life of the engine. I was really after an indication of likely service life of a GS 500 cam chain.

About pistons, in the past, I have always gone with a rebore to an oversized piston, but that was with tired single cylinders, where this was inexpensive and necessary. In this case, I'd rather not, because I suspect I'm going to find just stuck rings and no excessive wear, because the bike sat in a garage for years. Rings only is fairly common with cars and I can't see why it would be different here.

[HPP8140]

It's a GS500. I thought my 2002 would die multiple times after 20K miles....the bike makes noises and works inconsistently depending on temperature. My bike now has 89K miles...no rebuilds. I haven't done a compression test...I'm sure it's low, but the bike can still do highwayspeeds...not sure what is the big deal. it should last...just ride it and keep up with valve adjustments...imho