well im bleeding gutted this morning gsxr 400 gk76a

[minkathecat]

rebuilt a compleate engine and now its only making 35psi on compression test HOW dont ask me
new rings gas flowed engine stage one valves ground in proper tolerances all messured up
cam chain in right at 20 pins distance all new o ring in carbs everything tightened down right good spark only thing ive not changed is cdi box
WHAT THE HELL IS ALL THIS ABOUT IVE BEEN BUILDING ENGINES SINCE I WAS 16 AND IM 64 NOW THIS BIKE HAS NEARLY GOT ME BEAT !!!!!
ONLY THING I CAN PUT IT DOWN TO IS RINGS OR HAVE I BENT VALVES SOME HOW
lol

[Variablevalves suck]

Where did you get the cam chain setting of 20 pins from?
I know the bandit and 73a are 20 pin setting but I'm not sure the 76a is the same, I don't know/remember the setting but I got a feeling its not the same.
I use to have the workshop manual on the computer but it went belly up and I think it may have been different.
Not 100% sure or anything but seem to remember going over this before so would be worth a dig in the past posts.

[donk]

From the 76a manual

[Variablevalves suck]

Great to see you have a book, very few people have one for the 76a.
May have been the sp or more likely the later VC bandit then can't remember.

You going get loads of people PMing you for data now.haha.

So you say you only getting 35 psi on a compression tester, this on every cylinder?

[minkathecat]

yep 40psi on no 1 cylinder and thanks for photo copied it for book
but yes i have this set up on cam chain no 2 on exhaust port set to up position which is set square to the cylinder head top flange timing marks arrow on crank
no 3 on inlet is a bit well not quite square to head but it was like that when taken to bits
What i did find out cos it was only making 90 psi before rebuild which is not enough 140 psi is your limit AND BIKE SHOULD BE SHOVING OUT NEW 142-206 PSI ON COMPRESSION TEST was that the cam lobes where inlet -.031 inch down exhaust -.031 inch down on what i have in a bandit book which states
CAM LOBE DIA INLET SHOULD BE 1.2929 INCH INLET AND EX SHOULD BE 1.2811 INCH THIS IS FROM A BANDIT BOOK JUST TO FOLLOW MY 2 SPARE SETS WHERE SPOT ON TO THE BANDIT BOOK SO I USED THEM
hOWEVER IVE BEEN ASKING ON HERE THEIR CAM SIZES COS LIKE THE BLOODY RINGS THEIR IS A DIFFERENCE IN SIZE FOR WHAT MARKET dont ask me why?
Took down to head this morning so now im going to do a pressure test on each bore TO SEE IF ITS THEM BLOOODY CHINA RINGS
BORES WHERE CHECKED THEY WHER IN TOLERANCE so my bet is the cam shaft size their was a difference on the models market


ANY ONE OUT THEIR WITH CAM LOBE SIZES MIKED UP GIVE ME THE SIZES FOR GX76A MODEL AND TELL ME YEAR OF MANUFACTURE OF YOUR BIKE i WILL COMPILE A DATA SHEET OF ALL INFO SENT AND POST UP AT A LATER DATE

WHICH REMINDS ME THEIR IS ONE EMULSIFIER JET THAT TONY SLEEP DOSNT MENTION IN HIS EXELLENT WRITE UP this must be unscrewed and cleaned. alls well that ends well

[Variablevalves suck]

Is the 1.292 a lobe height size?
Do you say you have a second set of cams plus the original (different size) cams,
Can you compare then side by side on the bench?
I ask in case there are other differences other than the measurement.

[djheard91]

My lobe heights GK76a 1990 are about 33.3mm(1.311inch) for inlet and 32.8mm (1.291inch) exhaust. All base circles are 28mm (1.1inch). Used verniers but can't say they're the best measurements.

I would also say that I've only had the bike a few weeks and it is yet to run properly so I may not have the best cams for all I know

If your cam lobes are worn then you should be increasing compression as the exhaust valves wont be opening as much?

[minkathecat]

hi dj cam lobe dia yep those look to me to be correct AND ITS WHAT I HAVE FITTED
im going to do a pressure test next to see what the hell is going on here other cams where .031 inch down on size worn
so if i get the cylinder to tdc and put say 140 psi on it i will be a good indicator to where the loss is coming from
THEN I WILL MOVE ON TO CAM DISC TO SEE WHEN THEY OPEN AND CLOSE ON THE TIMING SIZE.
i dream of a gk76a manual using the bandit one as somthing to follow.

YOU ALSO GOT 20 PINS ON THE TIMING MARKS ? AS ABOVE PIC
I AM HOPING THAT ITS THOSE RINGS I BOUGHT FROM CHINA BUT WHEN PUT IN BORE THEY WHERE .025 GAP IN THE CYLINDERS
OR IT COULD BE THAT THE 1990 YEAR OF MANUFACTURE HAD DIFFERENT CAMS SAME AS THE RING SIZE IE BOTTOM SCRAPER 2MM DEPENDANT ON MARKET AIMED FOR

[Variablevalves suck]

Where is the info regarding different rings for differnt markets coming from.
the parts book lists the same number for rings since 1988.

The problem you will be having is that you changed the cam shaft and i could well be wrong but i'd put money on it being that one set of cams is pre 1993 and the other is post 93.

Suzuki changed the bikes from 60hp to 53hp in 93 and changed parts like the cdi, starter clutch and cams, amongst other things.

people come on the forum having changed the cdi with non starting and usually fix the problem by changing the starter clutch to match.

my thinking is the cams are different to allow for this so your timing is out, maybe valves are slightly open, lets hope.

[donk]

Great to see you have a book, very few people have one for the 76a.
May have been the sp or more likely the later VC bandit then can't remember.

You going get loads of people PMing you for data now.haha.

So you say you only getting 35 psi on a compression tester, this on every cylinder?

It took a long time to get one. I signed up to jauce auctions and got one from japan for about £20 delivered. I thought I'm not going to see that and believe it or believe it not it was on my door step in 4 days.

hi dj cam lobe dia yep those look to me to be correct AND ITS WHAT I HAVE FITTED
im going to do a pressure test next to see what the hell is going on here other cams where .031 inch down on size worn
so if i get the cylinder to tdc and put say 140 psi on it i will be a good indicator to where the loss is coming from
THEN I WILL MOVE ON TO CAM DISC TO SEE WHEN THEY OPEN AND CLOSE ON THE TIMING SIZE.
i dream of a gk76a manual using the bandit one as somthing to follow.
YOU ALSO GOT 20 PINS ON THE TIMING MARKS ? AS ABOVE PIC
I AM HOPING THAT ITS THOSE RINGS I BOUGHT FROM CHINA BUT WHEN PUT IN BORE THEY WHERE .025 GAP IN THE CYLINDERS
OR IT COULD BE THAT THE 1990 YEAR OF MANUFACTURE HAD DIFFERENT CAMS SAME AS THE RING SIZE IE BOTTOM SCRAPER 2MM DEPENDANT ON MARKET AIMED FOR

My manual is rl model only .if you go on jauce auctions tonight I've just had a look there are 4 or 5 of these manuals on there at the moment some of them cover all models. If I can help you with pictures ect I will but it's well worth getting one for 20-30 quid