77 gs400 to 87 gs450

[Brandon77gs400]

Hey guys I think this is as good of a thread to post about this as any. I purchased a 77 gs400 in August of 2015 I've been restoring it for the past year. I'm completely new to the mechanical aspect of bikes. Regardless I decided I could learn on the fly... well I've learned a lot. Mainly how not to do things. I purchased this bike from a friends father. It had been sitting for 12 years and the kick wouldn't turn over. He told me it was a "kickstarter pin" 'not a thing... Anyways after a lot of trial and error mainly error I'm here with a clean looking bike with great lines but now after everything I need a new engine. I refuse to let this bike go I've spent to many late nights restoring her just to walk away. So I have one simple question. I found an 87 gs450 Engine on eBay. Can I swap this engine in on my 77 frame? Will my carbs and exhaust match? I'm really hoping someone knows on here as it's kind of a specific question and I haven't seen anything related in my research the past few days. If anyone wants to see pictures of my bike please let me know! Thanks everyone!

 

[Oldman99]

Welcome to the forums!
Had to do some digging for this one, but I found an older thread with some grate info. The original poster wanted to just swap some parts from a 450 to his 400, but it moves to a engine swap being disused as well.
http://www.thegsresources.com/_forum/showthread.php?235955-Suzuki-GS400-to-GS450

 

[Brandon77gs400]

Thanks so much for the find! Very informative. I didn't think there was a ton of info on this subject. At least I was hoping not. I didn't want to look lazy asking questions already out there.

 

[Nessism]

What's wrong with the engine you have?

 

[Brandon77gs400]

I messed with it for a while and couldn't get it to stay running at the correct idle Rpms so to cut a corner I took it to a local shop that specializes in old Japanese bikes. (Great guys great place) at the very least I was told I need a new advance. On top of this the cam chain is to tight. I plan to take it apart one more time to see if anything has come lose to cause the bike to be next to impossible to kick over. If it's nothing in the upper part of the engine the guys at the shop said it's most likely a crankshaft issue.. so I figured I would put in the time researching a new engine as it may be cheaper and easier to swap then to replace the crankshaft. I'll no for sure this week if I'll have to or not.

 

[Oldman99]

If you can get the measurements from your 400, I'll get them from my 450 (in the morning) And we can see if you will need to do much fab work to fit the 450. (A is up and down wile C is left to right.)
I've seen some people say the 450 was just a factory bigbore 400 so I would hope they are close. Something about 400 and lower cc bikes being cheaper on insurance in Japan.

 

[Brandon77gs400]

I'll post measurements tomorrow morning as well that should really help. Just from looking at pictures they all seem to match up but the exact measurements are ideal.

 

[Nessism]

How many miles are on the engine and what has been done to it? Who monkeyed around with the cam chain tensioner? Oh, and the crank is almost bulletproof unless someone jacked around with it.

 

[Oldman99]

This is the measurements I could eyeball as my bikes still together except the tank.
A-22"
B-16"
C-7 1/2"

 

[Charlie G]

How many miles are on the engine and what has been done to it? Who monkeyed around with the cam chain tensioner? Oh, and the crank is almost bulletproof unless someone jacked around with it.

My thoughts exactly.....

 

[Brandon77gs400]

So I got the bike with 12k orginal miles. Trying to figure out why the kick wouldn't kick I tore into the bike to eventually find it was just the magneto flywheel. I replaced it and put the jugs and cylinder head back on set the timing but set it wrong. A buddy thought we should bump start it a horrible idea but we tried. I set the timing wrong so a piston kissed a valve snapping a valve off and then jamming that valve into the head. I replaced the head from a 78gs400 and got a brand new piston using original rings put it all back together set the timing correctly and it started but wouldn't idle properly. And was leaking oil from the cylinder gasket it also seemed to be burning oil in the left cylinder the one I was having issues with. I replaced all the gaskets and put it back together... it wouldn't start so I took it to a shop that's when they said the advance was busted and the engine didn't turn as easy as it should. Before I commit to buying a new engine I'm going to take it apart one last time reassemble and see how the engine turns. If it's still to tight I'll be looking to replace it. Trouble shooing is a bitch when you have little idea what it could be. Thanks for all the interest I love his bike and I'm absolutely commited to getting it going.

 

[Nessism]

If you are committed to getting the bike running we will help you. First thing you must do is purchase a factory Suzuki service manual if you haven't already. Not a clymers or Hayes. Next thing is to pull off the top end again. I strongly advise you to find a motorcycle specific machine shop and take the head to them for a check up. You gotta be sure there are no bent valves and that everything is sealing properly and install new valve stem seals. Then purchase new OEM Suzuki gaskets and seals for the top end along with new rings. Oh, and have the shop do a hone on the cylinder. Do all this and then we are getting somewhere.

 

[Charlie G]

I bought one of these new in 1977, same color but mine had the disc brake and a gear indicator. The cranks on these are ball bearing as far as I know and the later 450's weren't, so this is a more durable motor. My brother has one identical to yours with the drum brake. He's promised it to me, I just need to make room for it. Really can't wait to have it and to get it going. His, was purchased by my stepfather and was the bike that inspired me to buy one, which is why I'm here today writing. I'm of the mind these 400's are hard to find and especially in the condition yours appears to be in, not mentioning the motor. I don't think the demand (read "value") is great for them but I have seen blanket ads seeking them on C-list and the news papers posted by someone along the west, which makes me wonder.... I have a real soft spot for them. I'm not the best mechanic to seek advise from but if you make a concerted effort to get it going, the guys here will help you as they can. The hard road is to get the 400 engine going again. I'd take that road if it was me. Good luck. cg

 

[Brandon77gs400]

Well after inspection today I think I might be leaning towards new engine. As much as I would like to restore it it feels like the micahnic might be right .With both cams out its hard for me to turn the engine with the adjustment bolt.. im puttin tension on the chain so that the teeth grip it but it feels almost like something inside is warped. I'm gonna pull the head completely now and see if the problem still persists im not sure what I should do if it does.

 

[Brandon77gs400]

this is the bike without the head on it and as you can see it snaps back and forth as I rotate the crank. I assume it's warped just based on how it feels and looks. Any advice?

 

[Nessism]

Where is the cam chain? You can't turn over the engine with a wad of cam chain a jammed around the crank sprocket. Try holding up the cam chain with your hands and try to turn the engine over then. You should be able to spin the engine over by simply pulling up on the chain. The engine spins CW when viewed from the RH side.

 

[Brandon77gs400]

I held the chain up before making the video it felt exactly the same. I also tried to pull on the chain. What would happen is it was incredibly hard to pull and then it would give all of the sudden and then I would repeat with the same results. I didn't have this problem before taking it to the shop. I don't understand how this could happen.

 

[Guest]

I don't like the way this is sounding. I suspect your engine is toast. The bike looks nice though,
I have a 77 400 a 79 425 and an 83 450.. the 400 and 425 look like the same bike to me. Just a slight overbore. The 450 looks like an entirely different animal. I would be surprised if the engines would swap out. I've had no issues with engine internals yet, just lots of grief from carburetors that are gummed up from sitting 12 to 20 years.
Good Luck with your project. They are marvelous little bikes when they run right.

 

[Brandon77gs400]

I don't like the way this is sounding. I suspect your engine is toast. The bike looks nice though,
I have a 77 400 a 79 425 and an 83 450.. the 400 and 425 look like the same bike to me. Just a slight overbore. The 450 looks like an entirely different animal. I would be surprised if the engines would swap out. I've had no issues with engine internals yet, just lots of grief from carburetors that are gummed up from sitting 12 to 20 years.
Good Luck with your project. They are marvelous little bikes when they run right.

Does it look like the mounts are in the same place? And could the exhaust fit from one to another?

 

[Spyder]

Pull the stator cover off and try turning the engine again. You said you only had idle issues. If the crank were warped it would vibrate like a washing machine running at 2000 rpm. Could also be a bad bearing. I've had bad wheel bearing in cars that felt just like that. A machine shop should be able to fix almost any problem with the crank.