newbie HELP

[costa]

Hi My names James and im from the north east of England.

Iv recently bought a 79 gs 400 in a kind of flat tracker style. Anyway going off topic. Iv noticed the engine is only running on 1 pot (right side working) and the left is blugh. Checked timing and changed the plugs and points. checked compression are there's non.

Any way iv got the engine out and got the head off and then sacked it off for the evening. My question before I find the problem is what alternative engines fit? There are several 400 and 550 engines on eBay and depending what's wrong with my motor will the 550 engine fit the frame? are the exhausts headers and carbs different ect wiring. what can be used off my bike . its all about costs (and a little more oooomph) Any help appreciated

cheers
james

 

[Flyboy]

Welcome to the nut house, pull up a floor board and make yourself at home.
You will find more GS information here than you ever dreamed of, there are many, long time GS owners who really know these bikes intimately and are only to happy to share their know how.

The GS 550 is a four cylinder, will not fit your frame, the engine from the GS 500 would be a good swap out.
I would first find out what the problem is with your engine and go from there.

 

[costa]

sorry 500. new to GS bikes lol. will pull the head off tomorrow and get a proper look . Had a little peak inside while still in the frame and can see a what looks like marks on the bore. Also looks like it may have been machined in the past but till I can get it off wont know. Cheers for the reply

 

[costa]

also what other engines will fit. Is it just the 400 and 500??

 

[tkent02]

Just have to ask, did you adjust the valve clearances before you pulled it apart?

There can be no compression if the valves can't close.

 

[costa]

no we didn't...... will look into that tomorrow although I would doubt with my luck

 

[tkent02]

I have two bikes here right now that had zero compression, adjust the valvas and they are fine. It's extremely common.

 

[Guest]

Your stuck with that engine unless you want to modify the frame and wiring and completely fabricate an exhaust to use a gs500 engine.
They changed the design of the engine and frame in 1980. Its shorter and has no kickstarter.

You could do what some are doing here and install some gs850 pistons in it and bore the cylinders to match.

Its a bit of a boost but could be your last resort if your cylinders are already bored out too far.
Unless you can find some good used parts. (if yours are unusable)

You have some work to do before condemning your engine. The guys are right, Valve's will cause all kinds of weird issues that turn out to be just lack of maintenance.

 

[costa]

Right had the engine out and pulled the head and ......... the exhaust valve has a nice hole in the side approx 15mm x 2mm so we have the problem. That said the pistons/bottom end seam excellent and the rest off the head seams fine. inlet valves ect are good. just the left ex valve. SO going to change both ex valves but what else is needed with the gs850 pistons? just a bore out as necessary ? How much is safe on these engines to skim off the block to raise the compression slightly and any cams ect that are a straight swap? Iv got the engine apart and know a good machine shop so might as well get some oomph

cheers

At worst case its new valves and gaskets so a nice cheap fix

 

[Guest]

I've got no extra advice but want to see how you go with this. Any pic's to share?

If the bike has pods and an open exhaust to go with the tracker style, I'm guessing the PO didn't re-jet and ran it too lean... that would explain the hole in the valve!

Good luck and keep us up to date.

 

[costa]

My phones **** so no camera however get my new phone tomorrow so will get some pics up. Going to do a few jobs while its in bits hopefully but very interested in the engine upgrade as I have power issues

 

[Guest]

lol don't we all

There are a few threads about this mod going on.

Droice is one that comes to mind.

You'd need a new head gasket, pistons, and boring.

 

[costa]

seams quite an easy upgrade . does anyone know hiw much is safe to skim iff the head to raise cr . i will start a build thread over the weekend.

 

[Guest]

GS Twin

GS Twin

There is a GSTWIN website you could check out also. Nothing but twins and they have done about everything you can do to one. I used to go there (and Here) when I had my GS 500 it was a 2005.

 

[Guest]

Same guys frequent this side and that one.

But i've only seen the guys here do the 78's

Over there they focus more towards 89 and up twin.

look over my gs500 threads and you'll see some of the twin Tweakers

ben2go
fjbj40 is another one
droice
ummm who am I forgetting

 

[costa]

Cheers guys. Quite a lot off info out there that seams very year related ect. being a 79 when were these engines produced? ie 78-81 or much more specific. What year 750 pistons fit or is it all 2 valve 750 pistons fit the 2 valve 400 pistons?

well finally got my new phone so got some pitures.

however my photobucket is being awkward so cant upload till this week sometime.

Did find these on the laptop though.
How I bought it



Iv been speaking to a few specialists about the pistons ect from a 750 2 valve ect. still would like to know about hows best to raise the cr and whats a safe raise?

 

[Guest]

Looks good,

Your type of engine is from 77- 79. They changed mid 79 and stayed the same after that.
The only thing that changed after that was the top end.

Your bottom end is a roller bearing type and after 1980 it turned into a plain bearing type.

Your pistons have a 16mm piston pin and most after that have 18mm.

The gs850 is the only one with a 16mm wrist pin that is close enough to your engine bore so that you can use it.

There might be some other pistons that may work from the 750's from 78-79 but I don't know which ones.

 

[costa]

With the engine apart I have measured the cylinder walls and there a good 3/4" thick. Is it possible to get oversized 400 pistons and just bore the cylinders out to get the same end result? Lots off meat there? Sorry for all the questions but with the engine apart I think I might as well get on with it

 

[tkent02]

3/4 inch is incorrect. The thickness of the steel sleeve is what is important, not the aluminum casting. You will get an increase in compression ratio by going with bigger bore and pistons, without any head milling. How much? Do the math.
Not sure if the 850 is a higher dome piston then the 400 to start with, but higher compression 850 pistons are available.

Show us a picture or two of the burnt valve?

 

[costa]

Managed to photobucket to work in the office.







Easy to see and the valve is now on order as well as gasket kit. In theory could have it back up and running this week.