CB500T motor build. Opinions wanted.

[Useful Idiot]

Love the idea of engines having their own forum. I'll put the rest of my (re)build in the cafe section. So here goes:


2 seasons ago at a parade my local club was in, my bike puked a ton of oil out of the top of the motor. Not sure what happened. Maybe a return got blocked? I don't know, but I had other bikes to ride so I parked it. Now it's time to rebuild.


Initially I wanted to put a 450 big bore kit in it. Boring the cyls to 73mm, but from researching on the internet it looks pretty involved. You'll need to trim around 2mm off the piston skirts, while keeping the piston weight balanced I'm assuming and raise the head via a copper head gasket. If that will even work since I haven't seen anyone do it.


Looking at the pistons, the 450 is taller and the wrist pin location is higher. From right to left: 500T, 450, 450 black bomber

All this has me kinda thinking about leaving the pistons alone. Just get new rings, hone the cylinders and call it a day. I'd like opinions though. I have a little bit of money and a lot of time to throw at this bike.


That said, if I leave the stock pistons, the motor build would look like this:


1. New rings, hone cylinders
2. Mikuni 30's w stacks.
3. Cam regrind. Mild street cam from Delta Cams.
4. Torsion bars. Not planning on switching to springs, but I don't know of a source for new torsion bars.
5. Valves. Not sure about this one. I'd like new ones, but if my current ones are ok, I'll lap 'em and call it a day (I post pics when I yank the head off)
6. Pamco electro ing. I heard nothing but good things about it.
7. Exhaust. Thinking about a 2 in 1 with a small baffle.


So anyways, enough yapping. Here's some pics.


This is how it sat before the engine with south.

Pulling it apart. Weird thing was, when I removed the last bolt on the right side cover near the oil pump, it 'puffed' some oil out like it was under pressure, even though I had the drain plug out.

Cams coming out.

Intake side out. Notice the right side. Carb not set right?

Exhaust side out.

Intake followers were in pretty bad shape. Not sure if you can see the damage or not.

So the next step is to get the head off and inspect the valves. Order a new cam chain and send the cams out.


Also, I've found some little plastic pieces in the motor, I'm assuming they're from the plastic rings around the cams. Does it hurt anything NOT replacing these?


Does anyone know if you can get your cam followers rewelded and cleaned up?
What about a source for new torsion bars?
My cam chain tensioner sprocket teeth are pretty worn. Do they have aftermarket tensioners?


Thanks to Swagger for already helping me with some of this. More pics as I get further into the motor.

 

[Flugtechnik]

A couple quick things

Just get new cam chain dampers ( rubber ring around the cams. They are still available from Honda. They are actually rubber. Yours were so hard they felt like plastic.

I have not heard of any new torsion bars available. Why would you need new ones? Are they damaged? They should not "wear out".

If you get the valve seats recut, you will have to shorten the valves the same amount as the depth of the cut. The tolerances are very tight. If you just lap them in you should be fine.

I have some extra cam guides from my rebuild. Can send pics if you are interested to see their condition. I haven't heard of any new ones being made.

Copper head gaskets in varying thickness can be had fairly cheaply. I can't remember the website off hand but could search for it.

 

[Useful Idiot]

Thanks for the info.

The bars aren't worn out, that I know of. I just wondered if they'd lose their temper over time and that might lead to valve float over time???

 

[joevirus563]

Hey I HAVE A 450 BORED TO 74MM PISTON.

TORSION BAR DISENT REALLY WEAR BUT THE CAM FOLLOWERS DOES... MIGHT WANNA CHECK THEM. I MIGHT HAVE A FEW ONE IN DECENT SHAPE OR SOME TORSION BAR WITH CHAIN TENSIONER GEARS IF YOU NEED SOME.

Sent from my Nexus One

 

[joevirus563]

Re: Re: CB500T motor build. Opinions wanted.

Thanks for the info.

The bars aren't worn out, that I know of. I just wondered if they'd lose their temper over time and that might lead to valve float over time???

On my 450 I've grinded some of the teeth of the torsion bar to prevent that and to safely reach the 10k rpm quick and easy mod while you are there.
Sent from my Nexus One

 

[Flugtechnik]

Oh, another thing. There are thin washers (shims) that go on the ends of the camshafts to limit sideplay. Save these. You might want to buy some extras too. When you put the camshafts back in you have to put the cam covers back on *with the gaskets* and tighten them down to check the clearance. Can't remember the spec. These shims will account for different cam cover gasket thicknesses and possible wear.

 

[Flugtechnik]

On my 450 I've grinded some of the teeth of the torsion bar to prevent that and to safely reach the 10k rpm quick and easy mod while you are there.
Sent from my Nexus One

I've heard of this mod but decided not to do it because it seems like it would lead to more cam follower wear.

 

[joevirus563]

Re: Re: CB500T motor build. Opinions wanted.

Oh, another thing. There are thin washers (shims) that go on the ends of the camshafts to limit sideplay. Save these. You might want to buy some extras too. When you put the camshafts back in you have to put the cam covers back on *with the gaskets* and tighten them down to check the clearance. Can't remember the spec. These shims will account for different cam cover gasket thicknesses and possible wear.

For myself I didn't need them but it's good to have some.

Sent from my Nexus One

 

[joevirus563]

Re: Re: CB500T motor build. Opinions wanted.

I've heard of this mod but decided not to do it because it seems like it would lead to more cam follower wear.

Nop because the you cut teeth where the torsion bar is not laying on when the torque happen. TORSION bar dosen't seems to wear out easily.

I still have a few torsion bar as well if you need them.


Sent from my Nexus One

 

[Useful Idiot]

Thanks. Yea, I may do the spline grind thing. I think I saw a guy do it on hondatwins. I'll have to find the link.


I had a tiny shim on my exhaust cam that I kept. Do you guys know where to get these shims or did you just make your own?




Ok, so I pulled the head and cylinders last night. I found metal shards in the head and I'm assuming there's more in the bottom of the motor. Looks like this guy was the culprit.

It's gnarled up pretty good and I need to replace it. Do they even make replacement camchain followers? This one is toast.


The other end was in pretty good shape.

Here's the valves, they've got a bunch of carbon built up and the right side is pretty wet. I'm ASSuming that's from the carb not set right. I haven't pulled them yet, but they were siding out when I flipped the head. Again, I'm ASSuming they're not bent. Is there a proper way to check this? Maybe the acetone leak down test?

Cylinders look pretty good. There's some marking in there, but that's probably from the rings setting for a year.

Pistons looked ok as well. Just some carbon build up. Is a wire wheel safe to clean these with?

Still not sure about the 450 BB kit. I may try to find a junk set of pistons to get real world numbers about how much of the piston skirt is going to have to come off and how thick of a head gasket I'll need so the pistons and valves don't play kissy face. I've seen car guys do it with clay. I just wonder if the clearances are so close, what will happen at higher RPMs? Or is valve stretch an old wives tale?


edit: Here's the link for the spline grind: http://forums.sohc4.net/index.php?topic=35057.100

 

[joevirus563]

Re: Re: CB500T motor build. Opinions wanted.

Thanks. Yea, I may do the spline grind thing. I think I saw a guy do it on hondatwins. I'll have to find the link.


I had a tiny shim on my exhaust cam that I kept. Do you guys know where to get these shims or did you just make your own?




Ok, so I pulled the head and cylinders last night. I found metal shards in the head and I'm assuming there's more in the bottom of the motor. Looks like this guy was the culprit.

It's gnarled up pretty good and I need to replace it. Do they even make replacement camchain followers? This one is toast.


The other end was in pretty good shape.

Here's the valves, they've got a bunch of carbon built up and the right side is pretty wet. I'm ASSuming that's from the carb not set right. I haven't pulled them yet, but they were siding out when I flipped the head. Again, I'm ASSuming they're not bent. Is there a proper way to check this? Maybe the acetone leak down test?

Cylinders look pretty good. There's some marking in there, but that's probably from the rings setting for a year.

Pistons looked ok as well. Just some carbon build up. Is a wire wheel safe to clean these with?

Still not sure about the 450 BB kit. I may try to find a junk set of pistons to get real world numbers about how much of the piston skirt is going to have to come off and how thick of a head gasket I'll need so the pistons and valves don't play kissy face. I've seen car guys do it with clay. I just wonder if the clearances are so close, what will happen at higher RPMs? Or is valve stretch an old wives tale?


edit: Here's the link for the spline grind: http://forums.sohc4.net/index.php?topic=35057.100

they don't do camchain follower anymore. Maybe nos on eBay but will cost you both kidneys...

I might have a set of all those follower if you need them

Sent from my Nexus One

 

[Flugtechnik]

Nop because the you cut teeth where the torsion bar is not laying on when the torque happen. TORSION bar dosen't seems to wear out easily.

No, I meant the cam followers. By doing this mod, the torsion bars will have more torsion in them requiring the cam to have to push down harder on the cam followers to open the valves. I figured this would cause the cam followers to wear faster.

Just stating the reason I decided not to do it. I wasn't building a hot rod......yet.

 

[Flugtechnik]

Ok, so I pulled the head and cylinders last night. I found metal shards in the head and I'm assuming there's more in the bottom of the motor. Looks like this guy was the culprit.

It's gnarled up pretty good and I need to replace it. Do they even make replacement camchain followers? This one is toast.

Holy hell. Where are the teeth?

The shims are still available from Honda.

I used a wire wheel on my pistons (but that doesn't make it the right thing to do).

 

[joevirus563]

If i remember right some of the camchain follower are just rollers, they don't have teeth on it. I'll check tonight.


Sent from my Nexus One

 

[Useful Idiot]

Thanks joe. I'll pester my friends around here to see if they have one laying around.

According to this parts fiche there are supposed to be teeth on it, but I don't think this is correct.
http://www.cmsnl.com/honda-cb500t-500-twin-dohc-k0-usa_model463/partslist/E++05.html

 

[Flugtechnik]

I'm pretty sure that is supposed to have teeth. I have them sitting in my swapmeet box on my dresser at home.

 

[Useful Idiot]

You're right. It is supposed to have teeth. Holy shit!

 

[Useful Idiot]

Well, here's a problem. When I took the pistons off the rods I noticed that both top rings were broke.

There was a little scoring on the skirts. What do you guys think?

Exhaust valves.

Intake side.

The rods seemed to have a lot of play. I'm not sure what the tolerances are, I don't have manual in front of me, but I'm going to split the cases and go through everything.

 

[teazer]

Those pistons are OK as long as the skirt clearance is within tolerance, but they need new rings.

Wire brush the piston crowns and combustion chambers and valves.

Get the head an block "Planed" by your local auto m/c shop. It's a quick non precision process to get the faces flat and clean.

Replace the valve guide oil seals - those combustion chambers look oily.

Lap the valves quickly and see if they hold liquid. Use gasoline to see if it leaks past the valves into the ports. If the seats are badly pitted get the valves and seats cut.

Use a composite gasket -copper is cute but is harder to seal. Stock OEM is fine or get one from Cometic.

If you have lots fo cash go big bore, if not, just keep it as a long stroke 500. You can increase compression by milling a little more off the block or head. I like compression - it makes power from the basement to the top floor and helps to restore low end power lost with longer duration cams.

Try to get cams with short duration and a more lift than stock. The longer the duration the more bottom end you lose.

That intake was a mess and looks like blow back through that intake valve, so pay particular attention to that one.

Pamco has a good rep.

Sounds like a plan

 

[Useful Idiot]

Awesome teazer. Thanks.


edit: any ideas about how much metal you can shave off the head (safely)?