Compression?

[Craig380]

To echo Mike's point, the good news is that compression is pretty even across all 3 cylinders, without significant variation. That's a good thing, it means all cylinders are working evenly, and is another reason not to hurry to do a top-end refresh.

Personally, I would just use the Suzi pistons you already have. As far as the crank / bottom end goes, the seals tend to work until they don't. My 10 cents is, if you've no reason to open the crankcases, don't bother. If the gearbox oil doesn't smell of fuel, isn't milky with water contamination, and it's not burning gearbox oil, I'd just do the top end whenever you get round to it.

Maybe enjoy just riding the bike for the next couple of years until it really needs a repair? As mentioned earlier, it doesn't seem like there's anything seriously in need of attention, it's just the top end is maybe a little tired, but it will still give you many thousands of miles more.

I'm happy working on my bike, but I'd much rather be riding it

[Alan H]

Personally, I tend not to mend things that aren't broken. Sounds like yours are not even slightly broken.

[Eddie]

Thanks guys! this is what I was thinking, and wanted to hear, as I said earlier I will ride her till she cant go anymore, the compression check did scare me though but it runs fine, I think my biggest problem will be the left cyl. it had the lowest number and smokes more thank the others , but only until shes good and warm then it goes away but is still noticeable . Thanks for your help!

[tz375]

I wouldn't worry about those numbers. They are low compared to a good stock motor. I have never tested an actual stock motor because I usually skim the head somewhat and I often raise the exhaust port.

The closest to stock was around 133PSI, The more radical one is 165.

The next one came as 140psi and got new pistons because the old one were a bit of a mess. I'm pretty sure that if I had not rebuilt the motor, it would have run just fine.

I stripped another that was 160-170 and the two outer pistons were heavily seized and scuffed and it reportedly ran really well. That one will be rebored and the crank just came back from Bill Bune.

So the answer is "How long is a piece of string". If the bike runs well enough keep running it. When you are ready to do an engine rebuild, do a leakdown test to see how much the crank seals are leaking. If it were mine, I would do the crank anyway because I never want to pull another GT motor out a second time. The water pump is not an issue. Just use it again.

70.5 is first oversize.

Wossners are nice, but on a street motor CruizinImage are fine

Yes the center pot takes LEFT piston.

Back to the smoke. That has little or nothing to do with the pistons or bore. Unlike a 4 stroke, there is no Oil Control Ring. That extra smoke is most likely to come from a weeping check valve on that side.

[Eddie]

thanks tz, I appreciate all the help and info everybody gives me, I was just thinking the left cyl. might have lower compression because the ring might be seized up on the piston, or they are just tired, but the bike only has 16,000 miles on it, but either way ill ride till she wont run, I just hope she runs for a long time, shes the only daily bike I have, my other bikes are older and are smaller displacement (350, 250cc) and one had a full restoration, and the other is still in progress, but going from a 250 hawk to the gt750 is way different , gt750 can get out of the way of traffic faster than my little hawk,,, but I love riding the hawk just saying..