Craig380 wrote:There's quite a lot of difference between a YPVS and a 380 For one thing, the YPVS handles and stops, is lighter, and has an extra 15 - 20bhp
It does???!!!
I had one of those a few years ago. Wish I never got rid of it. The only faults I could say that let it down were that it handled terribly and the brakes were about as much use as using a handkerchief as a parachute. If the gt380 is worse than that I am wondering what I have let myself in for. Lol. I'm sure I will enjoy my Gita when it is re-assembled even if it does handle poorly though.
That's odd. My RZ seems to handle well and it stops almost as well as my GT750 which has modern brakes. It lacks the immediate bite but the brakes scrub off speed fairly fast. We strapped it to a dyno years ago and it made 56-57hp. They can be tuned to make much more than that Much more sophisticated than a GT750 and designed a whole lot later so that's hardly surprising.
I must admit that my old YPVS was a bit on the crappy side when it came to conditon. I sold it as I didn't have the money to give it the attention it needed. Maybe it was just a poor example
Mine is just about as fast as my mildly hot rod GT750, but it's quieter and more civilized. Unfortunately the foam air filter disintegrated and was swallowed by teh motr and spat out as dust. Now I need to replace the steel reeds with fiber - just in case. I picked up a new UNI filter with two layers of foam, and oiled it, so that should last another decade or 100 miles - whichever comes first.
Looks great, and great detail on your work. One question - was the cylinder head already in 3 pieces when you bought the bike?
Also, I did not know the 550 pistons had little oil holes on the skirts.
Thanks, its quite fun to drive..
The holes in the pistons is standard.. I have 9 pistons from the nikasil cylinders they are all the same..
The cylinder head is in one piece normally, as for the gt380. But i cutted it in 3 pieces, to make it possible to change on cylinder/piston. But also to make future head tuning easier..
2-strokes are full of speed,
4-strokes are full of parts!
oh right. So it is not a really necessary mod then. After having worked on KH triples before I wondered why Suzuki had make all three heads one unit and if it was one of those engineering gaffs that you hear about. Apparently not then
They can get head gasket problems, as the engines get older and the steel head studs start to fatigue the threads in the alloy cylinder.
Three separate barrels under a 1-piece head will only occasionally make a completely flat mating surface for the head. The sandwich-type head gasket will compensate somewhat, but you still get slight fretting vibration on the studs and head nuts which can loosen the studs in the cylinder, or the nuts themselves.
This is why Suzuki recommended checking the head nut torque every 2,000 miles. Some bikes don't need retightening, some do. Mine has always needed it, despite using genuine Suzi gaskets, new spring washers etc when I rebuilt the top end 7 years ago. Now one of the studs is pulling out of the threads in the cylinder, so will need an insert.
So I'm getting the head cut into 3 so I don't have to use an entire gasket set every time one cylinder has a problem.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
Well I finally got around to removing the head on the GT380 and found signs of head gasket leakage on one cylinder, but all three bores look okay and the pistons are standard. I'm planning on removing 0.5mm from the head and raising the height of the exhaust port by 1mm. I shall leave the rest as standard apart from the racing pipes and carb jetting.
Can anyone tell me how to tell if my head has been skimmed before? Please bear in mind I do not have the equipment to measure squish using water etc. I have a vernier and a tape measure. For example how deep is the squish area (that first lip before the compression chamber) on the head?
thanks
Tom
If there's a tiny lip or step from the edge of the squish area to the gasket mating surface, it is likely it has NOT been skimmed. On a standard head, that step is only about 0.5mm, it's very small.
On the 380s, at TDC the edge of the piston is only level with the top of the barrel, and the head gasket when fitted & compressed is about 1mm thick, so you can skim 0.25mm or 0.5mm off the head and be fairly safe with at least 1mm between piston and head.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
its std practice when tuning GT250 A's onwards to cut the heads in half and tuning 380's it also std practice too seperate them for any tuning and also helicoil ALL the barrel studs even if they are ok.
For one thing, the YPVS handles and stops, is lighter, and has an extra 15 - 20bhp
Much more sophisticated than a GT750 and designed a whole lot later so that's hardly surprising.
