Recommendations, boring, ballancing

[Mekanix]

Hi everyone,

The bike 1981 gs400l

What I plan to do is: (unless someone points me in a better direction )

1 Replace the pistons since it is very hard to get 400 pistons these days.
2 up the compression with wiseco 10.25-1 gs 750 4 valve pistons
3 balance the crank for new piston weight
4 remove the counterbalance shaft

Then of course fine tune.


Last year I completely rebuilt the engine but I had to re-use the pistons that were still good but close to the limit spec.

Now I find the bore is quite out of round and there is an occasional tic or slap from one side.

Id like advice and opinions on what I could do.

Right now the engine is stock with

67mm pistons 4 valve 56.6mm stroke
18mm wrist pin
17mm from deck to top of wrist pin
54mm total piston height
weight so far unknown.


I would like to use gs 750 pistons either 69, 70, or 71mm
not sure what year to use though, I don't have the specs per year.

Also I only have 4mm sidewalls so at 70mm I only have 2.5mm left.

I want to have the crank balanced for the new piston weight and if possible to have it balanced well enough to eliminate the counterbalance shaft.

Looking forward to your help

Thanks
Steve

[Steve]

What are you going to do to the pistons to provide clearance for the valves?

You said you were going to use pistons for a 4-valve head. They will have two pockets machined in the top for the valves.
Your bike only has a single valve, which will probably hit the raised area between the two pockets.

.

[Nessism]

That's a four valve twin Steve.

I'd keep the overbore to a minimum or the liners will get too thin, and don't mess with the crank...and keep the balancer.

The piston weight is no worry since it's close enough to where you are now, and getting rid of the balancer is a BAD idea since the engine will shake so much you won't enjoy it.

[Mekanix]

Thanks Steve, but unfortunately that's what everyone else thinks. In fact the gs400l doesn't exist outside Canada depending on which part shop you ask. but it is a tscc 8 valve twin

I get most of my parts from the gs450 such as bottom end, gaskets etc.

This time I'm looking for suitable top end parts from the 16 valve gs750 and a some performance.

The wiseco pistons are, i think 1mm higher than stock and that might require deeper recesses in the piston.



Thanks Nessism, I originally thought I could have the crank balanced well enough to eliminate the counterbalance shaft. But I haven't had the crank and rotating assembly weighed yet. I'm leaning towards the 69mm pistons so far.

[Steve]

That's a four valve twin Steve.

OK, my bad.

I did not look at the year, I just saw "400" and went with what I knew.

Actually, I didn't even know they made a four-valve 400. I knew there was a 500, but not a 400.

.

[Nessism]

OK, my bad.

I did not look at the year, I just saw "400" and went with what I knew.

Actually, I didn't even know they made a four-valve 400. I knew there was a 500, but not a 400.

.

500 twin is two valve Steve.

[Mekanix]

common honest mistake :P

[SVSooke]

Yeah the later 400 TSSC engines are a thing Canada got instead of the 450's.I like them but getting top end parts seems to be a problem.Got a gasket set from a local guy who told me if you order some stuff from the Suzuki dealer (eg:valve cover gaskets) you get 450 ones that don't fit.Have no idea if this is true.

[Mekanix]

That's true. I've completely rebuilt my bike last year and had allot of good posts here for parts that worked from a 450

Anything bottom end works as i recall. All gaskets, seals, parts...

On top end , only the head gasket. and even then its bigger and increases the combustion chamber size But works great.

Cant use the valve cover gasket
valve seals
breather gasket.
stud washers,

man I knew all of this last year :P
Hope it all comes back

[Graham]

You could use 750 pistons. You may have to shim the cylinder base or mill the tops to get the right piston deck height. If you change deck height than slot your cam sprockets (rat tail file) and degree in your cams.
The CB350 Honda had the same 180-degree crank style but didn’t have a counter balancer and the Yoshimura racing CB350s did something like 16000RPM. So yes you could drop the counter balancer and balance the crank. But you’ll have to plug the oil feeds to the counter balancer.
I’d resleeve bigger (there’s only two) and go for GS1100E big bore pistons maybe in the 80mm range. Now that would be fun an 80ish bore and a 56.6 stroke?

[Mekanix]

Now were talking


From what I've read (Google, gs400l service manual and 750 manual)1981 gs750es has the exact same piston dimensions.

Deck height 17mm
bore 67mm
stroke 56.6
pin 18mm

however the wiseco kits start at 69 mm and have a deck height of 18.5 and with the 750 they don't require anything besides install with stock head gasket.

As for the oil passages, they are screw in type jets that I can easily replace with allen screws to seal them off.


Now 80mm. If I had the sleeves and there was enough room and I had a head gasket.

that would make it 569cc 10.5-1 8 valve monster well compared to the stock 26 hp



75mm is the stock sleeve diameter with 4mm sidewall thickness
At 80mm that would mean i would need about 88mm worth of room.

[Graham]

Now were talking


From what I've read (Google, gs400l service manual and 750 manual)1981 gs750es has the exact same piston dimensions.

Deck height 17mm
bore 67mm
stroke 56.6
pin 18mm

however the wiseco kits start at 69 mm and have a deck height of 18.5 and with the 750 they don't require anything besides install with stock head gasket.

As for the oil passages, they are screw in type jets that I can easily replace with allen screws to seal them off.


Now 80mm. If I had the sleeves and there was enough room and I had a head gasket.

that would make it 569cc 10.5-1 8 valve monster well compared to the stock 26 hp



75mm is the stock sleeve diameter with 4mm sidewall thickness
At 80mm that would mean i would need about 88mm worth of room.

The machine shop that bore you jugs should be able to set in some GR650 sleeves or GS1100 Wisco sleeves and cut them down if needed. And Cometic does custom gaskets.

[GregT]

The valve sizes in the 8V 400 are a bit small for use on anything bigger than maybe 450 or so.
They're noticeably smaller than say a Kawa 500 twin.
The big motor is certainly possible but IMO performance will be limited.

[Mekanix]

Yeah they are quite small and its something I will look into in depth once I choose a bottom end solution.

I have found some 80mm jugs on ebay for a decent price

http://cgi.ebay.ca/SUZUKI-GS1100-1150-REPLACEMENT-CYL-SLEEVE-80-0MM-1323CC-/230470837574?pt=Motorcycles_Parts_Accessories&hash=item35a921e546

I have to take some measurements of the space I have available for resleeving.

[Steve]

500 twin is two valve Steve.

This is getting confusinger and confusinger.

I'm going to stick to answering questions about 850s and other shafties.

.