Hello
so I've completely rebuilt my 02 gs500 because there where lots of problems with it, it had low compression when I got it, it still runs but runs a little rough and tops out at 120kph so I did an engine rebuild, new pistons because they where scrapping against the cylinder walls, new piston rings, got the valves looking like new and it I was told by a mechanic that you can pour petrol into the valves to see if there are any leaks, did that and not leaks, the only thing I have to do is wait on the valve shims because two are at .13-.09mm but non of them are bellow .03mm so they cant leak compressions but I'm still getting around 100psi and I don't know what else to do, I'm pretty sure I did everything right because I bought the haynes manual for this reason before I started digging into the bike
anyone got any idea why I might still be getting low compression?
any help will be much appreciated
if compression test with oil (rings sealing)reads low its a bad gasket leaking or a valve issue
Can you tell us a little more about the rebuild process?
You said: "new pistons because they where scrapping against the cylinder walls, new piston rings,"
Is that new OEM Suzuki pistons and rings? Was there any damage to the cylinder walls? Do you have any pictures?
You said: "got the valves looking like new"
What does that mean? Did you replace the valve seals while
you had the valves out of the head? Do you have any pictures?
100 is low compression, should be more like 160 or 170 after complete rebuild.
Quote from: haybaler on October 16, 2024, 07:08:53 PMCan you tell us a little more about the rebuild process?
You said: "new pistons because they where scrapping against the cylinder walls, new piston rings,"
Is that new OEM Suzuki pistons and rings? Was there any damage to the cylinder walls? Do you have any pictures?
You said: "got the valves looking like new"
What does that mean? Did you replace the valve seals while
you had the valves out of the head? Do you have any pictures?
100 is low compression, should be more like 160 or 170 after complete rebuild.
before i started replacing stuff, there where decent scratch marks on the cylinder walls and on the pistons, i messured the pistons and sure enough they where warping outwards at the bottom and so i got new pistons and new piston rings and brought the cylinder block to a mechine shop and they said it dident need a rebore and it just needs a rehone and that the gap isent big enough for a bigger piston so i put it together fallowing the manual, cleaned up the valves and asked some advise before doing it myself and i was told if petrol dosent leak through the valves then they are holding a pretty good seal and after that i did the valve clearance and im waiting on some valve shims because there is too much of a gap in two of the shims and i check compression expecting that i fixed it and still got between 100 to 110 psi and yes i did buy OEM pistons and piston rings, i dont like cheaping out on vital parts like the pistons and for the valves, i dident get new valve seats, i just got some paste for valves and cleaned them up because the valves looked alright with not significant marks on them
i dont have pictures bc the bike is put together atm, i will be opening up the engine again later next week
Before opening,
if compression test with oil (rings sealing)reads low its a bad gasket leaking or a valve issue.
if you take it apart, you should do a hydraulic test to check the valve head is leaking
oil in the compression test should seal piston rings.
I just finished top end on mine, but I chose to send the head out for a machinist specialist valve job. He cut the seats and valves at slightly different angles and it needed about 25 miles of break in before it would start easily.
You said: "I will be opening up the engine again later next week"
That surprised me, I thought you might get the engine started and see if it needed some break-in miles.