Building GS425

[BrianH]

I'm re-doing my GS425 over the winter. I plan on taking the engine apart and re-building it. I want to use the stock cylinder bore.

Here is what I'm planning on doing so far.

Internal Inspection
Valve Job
Re-decking head and cylinder
Cylinder Hone
New Piston Rings
Adjust Valve Clearance



Is it worth putting anything else into the engine for performance gains while I have it apart? Con rods? pistons? Cam chain?

[cowboyup3371]

Why are you rebuilding it? Is there something already wrong with it or is it something you think you have to do?

[BrianH]

I'll have the bike all the way apart to do welding and a powdercoat on the frame so I figure why not. I want to know what I have in the motor. The motor is thirty years old.

[pete]

I'm doing my 450 at the moment and am in the reassembly phase right now.

One thing to do before you start is make sure you can get (at a minimum), all the oil seals and O rings for the bottom end. When I say make sure you can get them, I mean OEM ones, not aftermarket. Too many horror stories on here of Athena or Vesrah base gasket failures. Same goes for bearings if you need them. The general recommendation is everything OEM in the bottom end, and of course all over if you can afford it.

I'm not doing anything performance related with my rebuild, everything staying stock with regards to the engine, but I'm cleaning and checking things as I go as I also don't know any service history of my bike (got it from a pawn broker years ago).

Also, as you disassemble, make sure you know where every single nut, bolt, screw, bracket, washer, etc. came from by putting them together in a bag or tin or something and labelling them. I've already managed to misplace a couple of bolts along the way because I wasn't thorough enough disassembling.

The only possible performance gains I will get will be from K&N pod filters and a custom exhaust (and the expected rejetting pain), but I'm doing that for other reasons also, primarily appearance and avoiding the stock air box dance.

And finally, we need pic's, lots of them... as many as you can take in fact There's a projects and rebuilds section you can put a thread in if you want to track the whole progress.

[BrianH]

I've got all the seals and they are all in fact OEM so I guess I'm off to a good start.

I plan on documenting the whole deal so I'll keep everyone posted with pics as the build progresses.

How many bearings do you need for the crank, and how hard is it to take apart and re-assemble that thing to get them on there? I'm actually bidding on a stock replacement crank on ebay right now that looks to be in good shape just in case there is anything wrong with mine, especially with the bearings.

How about the cam chain too while I'm in there? My brain is just streaming ideas.

Don't sweat the re-jet too much its not as hard as some make it out to be, or at least on my bike it wasn't.

[Tech7]

Probably a little late now, but one of your best friends when completely going through your bike is a digital camera. Taking lots of pics helps when reassembing. Hardware locations, brackets, wire routing. I work in a restoration shop. Indispensible.

[pete]

I've got all the seals and they are all in fact OEM so I guess I'm off to a good start.

I plan on documenting the whole deal so I'll keep everyone posted with pics as the build progresses.

How many bearings do you need for the crank, and how hard is it to take apart and re-assemble that thing to get them on there? I'm actually bidding on a stock replacement crank on ebay right now that looks to be in good shape just in case there is anything wrong with mine, especially with the bearings.

How about the cam chain too while I'm in there? My brain is just streaming ideas.

Don't sweat the re-jet too much its not as hard as some make it out to be, or at least on my bike it wasn't.

Good stuff.

I can't really comment on the bearings though as I believe the 425's are roller bearing, whereas the 450 is a plain bearing...

[BrianH]

Thanks Guys.

I guess i'll figure the bearings out myself.

Using a digi camera to save photos of how things are assembled is a great idea. However, The majority of this build will be custom fabrication, a lot of frame work, new wiring harness, battery and electrical relocation, exhaust, bars, lights gauges pretty much everything.

I did take some close-ups' of the wheel lacing pattern so when i go to respoke the wheels I know what pattern to use.

I think I might add a cam chain to the engine build list and some bearings.

[Nessism]

How many miles on the engine? Unless it's a whole bunch you don't need things like a cam chain, nor a valve job.

Measure the parts and then make a determination.

[pete]

Apologies for my crap reply this morning, I was in a rush.

I decided to replace my cam chain based on age, advice, and the fact I had it completely torn down.

I got a DID for $US65 (shipped to Australia) from an eBay seller in the US.

Link is on the second page of this thread:

http://www.thegsresources.com/_forum/showthread.php?t=167786