Author Topic: GS450/GS500?GR650engine swap...  (Read 7824 times)

Offline djg42

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GS450/GS500?GR650engine swap...
« on: September 26, 2011, 05:37:52 PM »
Hello,
I hear you guys are the experts, so I was hoping you could help me out!
I am interested in swapping a GS500 motor in my GS450, or just using the GS500 top end. I read some of the threads and everyone says the problem is the GS500 exhaust comes straight out, hitting the GS450 frame. I have also read the GR650 head has similar exhaust outlets to the GS450. Could I use the cylinder off a GS500 and the cylinder head of a GR650? Does anyone know if this combo might work?
Thanks,
Dennis
« Last Edit: September 26, 2011, 05:52:51 PM by djg42 »

Offline The Buddha

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Re: GS450/GS500?engine swap...
« Reply #1 on: September 26, 2011, 05:51:00 PM »
I am working on fabbing an exhaust for the GR650. It could go between the frame rails and have a slide fit type deal into a pipe. I am yet to finish it though, but I have 3-4 of these GR650 in GS frame deals I will have to get em done right.
Cool.
Buddha.
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Offline djg42

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Re: GS450/GS500?GR650engine swap...
« Reply #2 on: September 26, 2011, 06:29:13 PM »
awsome, which GS do you have the GR650 top end in?

Offline crzydood17

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Re: GS450/GS500?GR650engine swap...
« Reply #3 on: September 26, 2011, 07:45:41 PM »
i still never got a answer if a GS450 8 valve head would fit on a GS500, Why would anyone want the 4 valve head of the GS500?
2004 GS500F (Sold)
2001 GS500 (being torn apart)
1992 GS500E (being rebuilt)

Offline Mauricio

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Re: GS450/GS500?engine swap...
« Reply #4 on: September 27, 2011, 09:32:19 PM »
I am working on fabbing an exhaust for the GR650. It could go between the frame rails and have a slide fit type deal into a pipe. I am yet to finish it though, but I have 3-4 of these GR650 in GS frame deals I will have to get em done right.
Cool.
Buddha.

Pictures? I often wondered about this. You are the first person I know that can give a definite answer on whether it can be done.

 :D
« Last Edit: September 27, 2011, 09:46:49 PM by Mauricio »
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Offline Mauricio

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Re: GS450/GS500?GR650engine swap...
« Reply #5 on: September 27, 2011, 09:44:10 PM »
Hello,
I hear you guys are the experts, so I was hoping you could help me out!
I am interested in swapping a GS500 motor in my GS450, or just using the GS500 top end. I read some of the threads and everyone says the problem is the GS500 exhaust comes straight out, hitting the GS450 frame. I have also read the GR650 head has similar exhaust outlets to the GS450. Could I use the cylinder off a GS500 and the cylinder head of a GR650? Does anyone know if this combo might work?
Thanks,
Dennis

My guess is that you are more likely to be able to swap cylinders, pistons, and heads from the 500 onto a 450 bottom end. The GS450, especially the latter motors ('85 and up) really are a smaller bore GS500. Previous engines had smaller bores but longer strokes and used a different crank altogether.

http://www.eurospares.com/gsfaq.htm

I had the coolest GS450, to this day I regret selling it. I came SO close to doing the 500 motor swap. I even had a pristine 500E motor for this, but I sold the bike and then sold the motor before trying.


« Last Edit: September 27, 2011, 09:46:01 PM by Mauricio »
"Nice and relaxed.
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360 aware, you don't know where or when
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but YOU ARE PREPARED."

Offline Big Rich

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Re: GS450/GS500?GR650engine swap...
« Reply #6 on: September 27, 2011, 09:58:24 PM »
I've seen that gs450 before......you sold out to a guy named Dan near the Philadelphia area, correct?
83 GR650 (riding / rolling project)

It's opener there in the wide open air...

Offline Mauricio

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Re: GS450/GS500?GR650engine swap...
« Reply #7 on: September 27, 2011, 10:00:52 PM »
YES!

Dan H.

I've regretted that sale ever since. I just couldn't handle two projects at the same time without a garage and decided to part with the 450. He sold it not that long ago, that bike was a bit small for him anyway.

I hope it is in good hands now...  :icon_neutral:
« Last Edit: September 27, 2011, 10:02:13 PM by Mauricio »
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Offline werase643

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Re: GS450/GS500?GR650engine swap...
« Reply #8 on: October 10, 2011, 12:55:51 AM »
the original 555 big bore kit was not intended or designed for the GS500E..... it was for the GS400-425-450 based engine.
want Iain's money to support my butt in kens shop

Offline harlton

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Re: GS450/GS500?GR650engine swap...
« Reply #9 on: October 13, 2011, 06:36:27 PM »
I have been fiddling around with this for a while, I have a gs500e complete bike. I also have a complete gr650 engine, plus 2 425 4 valve heads.  physically they will all bolt on with small amount of work.  I am having exhaust issue's now and I am still working on that.
      As to what heads what, the gr650 and 500 head I have has the same size valves in them and look very similar, I have not cc'd or flowed them yet. 
      The 4 valve head has very small valves in it, so I am disappointed, that there is very little curtain gain to be had simply. I am a bit behind on this project due to some unforseen health issue's (old fart).  If anyone is interested I can publish or share my findings, plus I have done a few mock up's on engine pro. Let me know if you are looking for if anything in particular and I will dig it out.

Regards Ian

Offline werase643

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Re: GS450/GS500?GR650engine swap...
« Reply #10 on: October 15, 2011, 02:00:45 PM »
do you have the 4 valve heads(425) or the 4 valve per cylinder heads(425)....8 valve head
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Offline harlton

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Re: GS450/GS500?GR650engine swap...
« Reply #11 on: October 17, 2011, 02:23:50 AM »
 I have the 4 vavle/cyl or 8 valve heads.

Regards Ian

Offline Chuck78

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Re: GS450/GS500?GR650engine swap...
« Reply #12 on: November 19, 2019, 03:55:02 AM »
4 valve per cylinder GS425 heads???? I've head of 4 valve per cylinder 1980+ GS(X?)400 Canadian heads,& the 89 or so GS400E which appears to be just a smaller bore GS500, never heard of an 8 valve 1980+ GS425 twin?????

Also, weren't those big bore pistons a Kawasaki (GPz?) big bore piston? But then Wiseco change the piston dome design some, and they still worked for the bike they were intended for, but no longer fit a GS500 head at all.
They were definitely not for a GS 400 / 425, you cannot physically put more than a 74 or 75 mm piston in those, and THAT requires re-sleeving, and you'd have to have a bushing machined to fit a 16mm piston pin through the GS 450 / 500 rod that is designed for a 17mm or 18mm pin.

to better answer your question, no, you really don't want to try and fit a GS500 head into a GS450 frame, as the exhaust ports point literally straight at the frame rails. I have seen this done once, but the exhaust was severely restricted by a tight 90-degree bend directly out of the head, which is very far from ideal. Or you could chop the frame! Another major faux pas in my book. Just get some custom JE Pistons made for the GS450 head, in the largest bore size possible for the GS500 cylinder - aren't they 74mm stock? Or 75mm? +2mm would be very reasonable and a big bump up in displacement for a 450, + 3 mm would be nice, +4mm may work but may also run a lot hotter because of thinner cylinder walls. +2mm or +3mm would be ideal.
since they will be custom-made, you will want to very carefully check out the deck height differences, or rather the compression height differences on the pistons, as I believe I have seen someone have to make up a custom thick aluminum base gasket spacer and run to base gaskets, one on either side, Stephen on the GS resources, AKA Mechanix.
I believe the problem is that the GS500 runs a shorter deck height or shorter cylinder height. You could also just measure the height of base gasket surface to head gasket surface on the cylinders, and shortened the new piston from the GS 450 compression height down to what is needed for the 500 cylinder.


just to throw some other info out there, I know you are talking about a different 400 or possibly 425 head with eight valves, but the early 404 25 as many of you probably know has a different stud spacing than the 450 and 500 use, the center stud in particular are much closer to the cylinder bore, hence you can only go so big on a GS 400 / 425 when re-sleeving for big bore pistons. Around 489cc, or 502cc is the reasonable limit on the early 2v/cyl 1970's GS400/425. 449cc for stock 400 sleeves. Maybe 462cc for 470-somethimg cc for a 425, but I'd not count on that without doing some serious research with the parts in hand. I think the 425 sleeves are thinner than the 400 sleeves. 

I have never heard of someone using a GR650 head with GS550 pistons, but that would be exciting news if it were do-able, however you barely get enough cam chain tunnel oil drain back sealing if you run the GR head on a GS cylinder. It will seal when newly installed, but you are likely to have some seepage of oil perpetually at some point in the distant future, as there is just a sliver of overlap in the pattern of the head vs. cylinder at one point.
« Last Edit: November 19, 2019, 03:59:40 AM by Chuck78 »
'77 GS400B racer project 489cc
'79 GS425E canyon carver project 449cc