Topic: Exhaust guides as intake guides

[bomellberg]

Hello experts,

I have searched the forum for an answer to this questions but haven't found any.

True, the exhaust guides are twice as expensive as the intake guides; why would anyone use them as intake guides?

I'm replacing all my guides an came across 7 exhaust guides and 2 intake guides here in Sweden. Would it be
possible for me to use 2 of the exhaust guides on the intake side? Maybe machine them to the same length?

CB500 Four K3, 1978.

Thanks,

/Bo

[69cb750]

You need to measure od with micrometer to check sizes.
Buy the guides you need.

[bomellberg]

You need to measure od with micrometer to check sizes.
Buy the guides you need.

Will do!

[MRieck]

Hello experts,

I have searched the forum for an answer to this questions but haven't found any.

True, the exhaust guides are twice as expensive as the intake guides; why would anyone use them as intake guides?

I'm replacing all my guides an came across 7 exhaust guides and 2 intake guides here in Sweden. Would it be
possible for me to use 2 of the exhaust guides on the intake side? Maybe machine them to the same length?

CB500 Four K3, 1978.

Thanks,

/Bo

I have used intake guides on the exhaust side many times are they are generally shorter when using OEM. Also use intake guides on the exhaust side if the original exhaust guide guides did accommodate a guide seal i.e. 400F. The ID's have to be honed (or reamed but I'm not a fan of that) for final fitment anyway. If you have a lathe you can increase the taper of the guide that is exposed in the port to help airflow too.
 Aftermarket 550 guides are all the same length....they are just shorter on top for increase retainer to guide clearance for larger cams.

[newday777]

Welcome aboard the forum Bo
I don't know if they can be machined to work or not.
But CMSNL.com in Nederland has them both available.

Have pulled the cylinder head apart and measured the guides and valves to see if all of the guides are out of spec needing replacement? I think it's a bit unusual to find all needing replacement.

Isn't your bike actually a CB550? That was the K3 in 78, not a CB500.

[bomellberg]

Thanks MRieck for that comprehensive reply!

My use case is the other way around, exhaust guides as intake guides, but if I read you correctly, as long as I fit them for the valves properly there should be no issue.

As far as machining them, I don't know if it is possible without special lathe tools, since they are made of hardened steel.

@newday777 Thanks for the welcome. It is indeed a CB500, the "European extended" version.

https://www.classic-motorcycle.com/Content/Bike/honda-cb-500-four-1978-498cc-4-cyl-ohc/a0235


Not my bike, since it is in atoms at the moment. :-)

[bryanj]

Not sure but i think you may find inlet valves donr close properly if exhaust guides fitted because of extra length, the extra length will also alter air fow in so if it does work mechanically i would say all need to be the same

[bryanj]

Also if yours is the same as the picture it is basically a 550 engine with 500 cylinder and pistons

[bomellberg]

Not sure but i think you may find inlet valves donr close properly if exhaust guides fitted because of extra length, the extra length will also alter air fow in so if it does work mechanically i would say all need to be the same

Right. Thanks for mentioning that. As the intake valves are bigger, the rounded area of the stem is protruding further up, so they could very well interfere with a longer guide.

I will measure them thoroughly and machine them to math their intake siblings.

Also if yours is the same as the picture it is basically a 550 engine with 500 cylinder and pistons

I'm not sure. I read that there is a 3 kg difference between those engines. Can the cylinders and pistons make up for that?

[MRieck]

Thanks MRieck for that comprehensive reply!

My use case is the other way around, exhaust guides as intake guides, but if I read you correctly, as long as I fit them for the valves properly there should be no issue.

As far as machining them, I don't know if it is possible without special lathe tools, since they are made of hardened steel.

@newday777 Thanks for the welcome. It is indeed a CB500, the "European extended" version.

https://www.classic-motorcycle.com/Content/Bike/honda-cb-500-four-1978-498cc-4-cyl-ohc/a0235


Not my bike, since it is in atoms at the moment. :-)

Those OEM iron guides cut like butter on the lathe....no swarf....just dust particles as it cuts.😉