TSCC GS400 Big Bore

[n780]

I'm at a bit of an impasse with my 1983 GS400E (Canadian model, 4 valves per cylinder)

It's my first bike and I've learned lots from it. Went through the charging woes, learned how to do valves and can disassemble the carbs with my eyes closed. I'm still playing around with the look of the bike but, in the end, I want something with a bit more power.

I can't afford a new bike nor do I really want to get rid of this one. I've found several threads and even kits for boring out the late 70s two valve per cylinder models with 750, 850 or 1100 pistons but nothing for the 400E. And I'm no wizard yet, like I said this is my first bike. But I'm willing to read, put in the time and do it right. I just need something to work off.

Could anyone supply some info or resources for such a project? Or maybe talk me out of it? The rain is coming for the winter and I need to keep my hands busy.

[Guest]

My links below, Happy reading :P


How crazy do you want to go ?

[eil]

I won't try to talk you into or out of upgrading your current bike, but I would advise you to research the costs first... Not sure what the market is like in your neck of the woods, but around here it's way cheaper to buy a running vintage bigger-engine bike (especially GSes) in good condition than it is to rebuild an engine on something that already runs fine.

If you love your current bike and want the experience of an upgrade/rebuild and don't mind the associated costs, however, then sure, for it.

[Guest]

Read Mekanix's thread and see what's involved... if you reckon you're capable, go for it!

I know that when I get a second bike and my two valve 450 gets a bit tired I'll be seriously contemplating a fun engine to drop into it...

[n780]

My links below, Happy reading :P


How crazy do you want to go ?

Exactly what I was looking for, thanks.

I'll need a bit to go through it all and digest the necessary work, but I didn't foresee CNCing pistons...

On a similar note, perhaps I should consider sourcing a neglected 500 engine and going for a rebuilt and drop it into the frame. I'll start looking into if that fits at all, unless you guys have some insight.

[Guest]

Exactly what I was looking for, thanks.

I'll need a bit to go through it all and digest the necessary work, but I didn't foresee CNCing pistons...

On a similar note, perhaps I should consider sourcing a neglected 500 engine and going for a rebuilt and drop it into the frame. I'll start looking into if that fits at all, unless you guys have some insight.

I have both the gs500 and the tscc 400, They are both pretty even. In terms of performance. Even though the 400 is heavier with a backrest, windshield and crash bar.

One thing that I would do though is get a set of slingshot carbs from a 500 with k&n Filter and a Mac Exhaust. It would wake up the engine quite a bit.

The 400 already puts out enough power I find.

But if you want to go that route,

Use your base with 500 cylinders, pistons, cam's and a 450 head (for the side exiting exhaust ports). Then fit the head with the 500 valves and port it for them.

*** There are a few people here that have done the 450-500 swap already just like this.***

Carbs, filters, jet kit for the 500 carbs, 2-1 Exhaust, All should be your first things to get and they will compliment the engine mod's where as the original stuff will restrict it.

If you can afford it, FCR 37's are the recommended carbs to go with.


One thing that makes the original carbs open up a bit quicker is reducing the length of the slide springs by half an inch.
It makes the engine feel like its trying a little harder where it would normally feel like its under full load.

I know with mine, that it would only pull so much. Even at wide open throttle the carbs would only allow so much flow until the RPM's increased.



If you want to keep the 8 valve head, and get the 500 cylinder block you can easily get some pistons made for it, It would be about $3-400 for pistons alone but its cheaper than what I did.
I bought gs1100 pistons and then machined the valve reliefs in closer to the center because of my head design.

Rapidray could get the pistons made for you from CP pistons. They just have to be the same as a 16 valve GS750 pistons in every way except with a larger diameter. That way the valve reliefs are in the same place and will work with your stock cam's. You could go up to 75mm with that block and have 3mm left which would be safe. That would make it a 500cc.

But the compression ratio would jump from 10.5:1 to 12.7 which is too much for that head. (they have a tendency to crack between the plug and exhaust valves)

So your going to have to open up the combustion chamber by 5cc's each to bring it back down to 10.5. Or if you want to leave the head alone you could raise change the piston to head clearance but that would effect your squish clearance and you'd loose power that way.









There is allot to it if you want to take the time to do it. It takes a good plan to start off with.

So for parts around the engine:
Carbs from 89-2004 gs500
lunchbox filter from k&N
Donojet kit (just for the needles really but the whole kit is useful)
Exhaust, Only one I know of is the the MAC on ebay.
GS500 ignition system, is a nice solid state upgrade.


Inside the engine:
8 valve way assuming your keeping the original cam's and original red line (so you don't have to change the springs) and stock head.
Get the pistons made the same as your's ( gs750 are identical) to what ever size you need.
Get the gs500 block.
Measure how tall the gs500 block is and how tall yours is. ( there is a difference)
Choose your gaskets. ( the gs500 and gs400 head and base gaskets are identical except the 400's are thick paper/fiber and the 500's are 0.010" thick and are metal)
Selecting the right gasket raises or lowers the head so that the squish clearance is the same as it used to be whith the original pistons.

You need to set the block so that the top of the piston is level with the top of the head and then select the right head gasket thickness.
Then call up COMETIC gaskets and have them make you one the right thickness. (order 2 just in case) They have the template for a gs450, Use that one.
Now assemble the engine and check the piston to valve clearances.
Put some clay in the valve releifs and turn the engine over several times.
Check your clearances and you should have the same as the original pistons had.
Now the issue with the combustion chamber being too small for larger pistons can be fixed by opening up the chamber a bit. From 3-5cc's. Stock is 17cc's total. You need 22cc's for a 75mm bore. Mine was 27cc's when I was done.

Re-assemble the engine and check your cam timing. 104 degrees intake 107 degrees exhaust is stock I believe and would work just fine. I'd go even lower though. Around 100 100 for more mid range punch. Higher gives you more top end but you won't need it since you won't be in that rpm band.


4 valve way
Get the gs450 head and cam's.
Get the 500 base and get the 500 pistons.
Choose the best gaskets to get the piston height just right.
Compression will be higher than normal but not enough to be a problem.
Check the piston to valve clearance.
Check the cam timing when your done.

The 450 head has a lower head volume than the 500's head and it has a combustion chamber shape that lets you use what ever big bore pistons you want to use from one of the other bigger bikes. ( the 500's head is a weird shape) You can use 500 pistons with a 450 head but not the other way around.
The 500's pistons are not as tall as the 450's so that lowers the compression ratio and using the 450 head doesn't change the compression ratio enough to worry about.
Get the 500's cam's, They are slightly taller than the 450's cam's. (if you want to. But the 450's are good enough)


One more thing, try and get the pistons made close to the same weight as your original ones so it doesn't vibrate more than it did stock. A little heavier is ok.

Yours vibrates allot at 5000rpm and smooths out at 7000. With mine I went with heavier pistons and that made 5000 rpm smooth but slightly buzzier at 7000 that I don't mind. I'm finding that the lower RPMs are nicer to ride in.

[n780]

Ok, I'm still digesting everything you've dropped there but it's great info. If anything I'm reconsidering it all as I don't even have a garage, just a tent covering my bike out back...

We'll see.

One thing that I would do though is get a set of slingshot carbs from a 500 with k&n Filter and a Mac Exhaust. It would wake up the engine quite a bit.

If anything, this is the first thing I'll do. I have K&Ns and a Mac 2 into 1, but what carb model are you referring to? RS 33s? And is this the type with the accelerator pump?

I have good low and top end but tuning the midrange is not the best. To this day and before I made any modifications I've always felt some hesitation when quickly rolling the throttle.

[Guest]

Ok,
If anything, this is the first thing I'll do. I have K&Ns and a Mac 2 into 1, but what carb model are you referring to? RS 33s? And is this the type with the accelerator pump?

I have good low and top end but tuning the midrange is not the best. To this day and before I made any modifications I've always felt some hesitation when quickly rolling the throttle.

They look like that

A few tips:

When your tuning stock carbs in the mid range, the one thing that makes a difference is the slide spring length. Or drilling the hole in the slide but that is tricky to get the right size.

With these GS500 carbs all the tuning is the same as with yours but instead of having the shorten the slide spring or drill out the slides to change the mid range, you can add restrictors to the slides. By changing the or removing restrictors, it will either speed up or slow down how the slides move.
Stock they are almost wide open. The Dyno jet kit comes with the restrictors and I found it gave the smoothest feel with both of them installed.

https://www.youtube.com/watch?v=DbzWS76bpfU

https://www.youtube.com/watch?v=wRDvhU88J1Q

https://www.youtube.com/watch?v=uK51lr-vFjg

https://www.youtube.com/watch?v=isjHoABXNT0

That was before any tuning and I'm waiting for a cheap set of carbs to come on ebay before I swap them on.



If your going to do any engine work, you might as well remove the engine and bring it inside. Its not good to have it open to the elements.

I did all my work in this closet :P

And kitchen :P

[Guest]

Slingshot carbs.

http://gstwins.com/gsboard/index.php?topic=56601.0

[GS450L-1982]

These are some great mods! do you think any of them would work on my 1982 GS450L? Would the GS500 carbs fit on my bike?

[Guest]

How about the big bore Kit and a small turbo???

[n780]

Well, I have the slingshot carbs off a 91 500E on my bike. Since I had no airbox I accepted that I needed to purchase any k&n filter (the ODs airside on the 500 carb are significantly larger.)

Ended up going with this filter:http://www.knfilters.com/search/prod...x?prod=ru-2970 It works... but is too big for the frame where it sits. I had to dent in on both sides a touch to have it fit on snug to the cab.

Two sizes up on the main and it pulled really well in the upper throttle range. But, I'm having a problem with one of the floats or needle seats or something. Blipping throttle causes a big hesitation, cold starting is pretty much impossible, have to let it get well above freezing or better yet sit in the sun and at low rpm it's super sluggish with random surges.

Checked for air leaks: nope. Spark and compression good. Went to drain the bowls and one only had a few drops in it! Tore off and redid the heights, same problem in one bowl.

So, have a set of o-rings, needles and seats on their way. Once I have it running right I'll finally be able to report back.