GS450 to 500 swap questions

[diptenkrom]

I have bought some of the parts already. and i am ramping up to doing this swap soon.

I have a 500 cylinder jug and pistons, as well as cams and a badly running 1981 GS450 scrambler build.

I read elsewhere that the head studs from the GS500 were better, so i will be ordering those

My biggest question is the cams. how do i figure clearance for the valves, ;and how do i know what needs to come off the piston to make valve clearance?

i do plan on using GS500 carbs or some other upgrade, and i know there is a mix of gaskets and what not to make this work. any advice would be appreciated. I have been reading about this here and there for like a year, but no real clear answer on the piston to valve clearance that i can find other than it needs to be done.

[GregT]

There's no definitive answer about valve to piston clearance. This is because all the parts you are going to use will be already used and the head for instance may have been machined. The safe way is to mock up the top end on the motor with plasticine on the piston(s) and turn it over by hand. Cutting the plasticine with a craft knife will tell you how much clearance you have. Ideally you want at least .060in both sides.
That said, if it's a street motor and the head hasn't been machined the inlet usually measures up around .045 -.050in. If it's only going to be used on the street that is safe IMO.
If it's a race engine or will see track days then it needs the full .060in. Any hot cams will need the pistons machined. And probably better valve springs.

[diptenkrom]

Thanks GregT, the bike is in a bike that I am building for a scrambler bike. It will not be doing anything serious, or raced or anything. It was just not running right, and i figure that i am going to tear into it, and the parts are cheap enough, i might as well squeeze a little more out of the bike. This is just a low buck extra bike project that i have been stagnant on since reshimming the valves didn't get it running right. My first bike was a GS500 and i liked the simplicity, but i liked the look of the older UJM bikes and i found the right deal for $500 about 2 years ago, and tinkered for a bit, and now it is something i want to get going. it is not my only bike, but it is part of my "ideal garage" so i would like for it to be reliable. Any added info there would be greatly appreciated. I plan on new gaskets and seals and i have already ordered NOS valves and will be taking the head to the machine shop for trueness and valve work before assembly.

Is there a guide in general on how to do the valve clearancing? i read a few places that the cams really made a difference on an otherwise stock GS450, so i dont want to leave that part out.

[GregT]

Once the bottom end is together, mock up the top end. You only need one piston in for a trial assembly.Don't even need rings or pin circlips on it. Don't torque the head down, just a light nip. Plasticine in the valve pockets or at least on the piston crown under the valves. Time up the cams as per the manual and turn the engine over slowly.
Pull the head off and you'll see where the valves have hit the plasticine. Cut it with a craft knife and measure the thinnest point. I use a vernier caliper with a dial gauge attatched but a simple depth gauge will do.

[diptenkrom]

first of all, Thanks!

so they wont hit enough to cause any damage like this? i assume i should have the cam caps shimmed to spec first?
do i just use a dremel with a sanding barrel? it sounds like im not removing a lot of material, but should i be real concerned that they will not necessarily be equal on each piston? is there a better way?

also never used plasticine, is plastilina pretty much the same thing? https://www.amazon.com/Sargent-Art-P.../dp/B00FR7TQOM

[GregT]

Yes, that stuff looks like it would work. Yes, valve clearances shimmed correctly. Turning it over quietly by hand and not forcing it if things hit is safe. If material has to be removed from the piston crowns, it's best done in a mill.

[diptenkrom]

Thanks for all the information! Now i just have to starft taking things apart! hoping to get that done this weekend. would be nice to get to the point of riding this bike in a month or 2... instead of it sitting here for another 2 years

[LAB3]

When I looked into doing that swap on my 450 the folks over on the gs500 board gave me a lot of good advice, you might want to check out what they have to say.

https://gstwins.com/gsboard/index.php

[diptenkrom]

When I looked into doing that swap on my 450 the folks over on the gs500 board gave me a lot of good advice, you might want to check out what they have to say.

https://gstwins.com/gsboard/index.php

I have looked around that board as well. I cant find your posts there, what was your username there so i can search?

did you go through with it?

BTW - I finally got the engine pulled this weekend. hope to tear into it sometime this week, valve cover is off, that is alli got done

[LAB3]

I've never did anything on my 450 that deviated from stock just relaying the conclusions I had come to. The position of the exhaust ports between the two frames is about the only thing that separates the two engines.

[diptenkrom]

Anyone know if there is a way to add an oil cooler to the gs450 engine? Just a though I had while it is apart, and I live in the south, it gets hot here for a large part of the year.

[GregT]

Anyone know if there is a way to add an oil cooler to the gs450 engine? Just a though I had while it is apart, and I live in the south, it gets hot here for a large part of the year.

It could be done. Two possibilities. A takeoff from the oil pressure sender cover behind the cylinders. I suspect a takeoff made for a GS1000 would work here.
And an oil filter cavity cover from a late GS1150 with the cooler takeoffs would probably work too. I think the bolt pattern is the same.
The concern I have is the oil pump capacity. It's a plain bearing motor and any drop in pressure while filling the cooler on startup could get expensive. No easy way to increase the pump capacity either.

[Grimly]

It's a plain bearing motor and any drop in pressure while filling the cooler on startup could get expensive. No easy way to increase the pump capacity either.

I suspect that's the reason why the XJ900 has an oil level light instead of a pressure light. The oil cooler is rather daftly mounted pipes-downward, so it drains when sitting.
Not that it's done the engine any harm in 100K, but owners would have been worried about the light delay on startup.

[grcamna2]

How has your project been going so far 'diptenkrom' ?

[diptenkrom]

How has your project been going so far 'diptenkrom' ?

Sorry for the late response... a lot has gone on in my life, but not a lot with the bike.

slowly, lol. I have the motor apart, the head has been machined flat with NOS valves and a 3 angle job. I have put the 500 jug and pistons on, i left th old base gasket on for thickness to be right. i have the plasticine, and i have the valves shimmed, (if i recall i need to remeasure, as i think one is borderline, and the feeler gauge kit i had at tthe time was less complete.) I have all the gaskets and hardware to put it together. the weather has not been friendly, and i have a bit of extra stuff in my shop at the moment. i had to get my GoldWing road worthy as i took a trip on it back in Oct. I also bought a Kawi Concours 1000 with fuel leak issue for a trip hopefully in the late spring, that i will sell afterwards. anyway i am now splitting time i have between the GS450 and the 79 GS1000
i am front end swapping. I came back to this thread to refresh my memory on the GS450, as i hope to put some time into it this coming weekend. Doing the plasticine test should not take more than a couple hours, if i can get a bit of a hand from someone to help me keeep things from moving aroudn too much.