Rebuilding the Honda 150cc Head - The Valves

[Smithers]

There isn't really all that much information on the internet about the smaller displacement Honda motorcycle heads. Mechanics don't really go taking pictures of their work and tell people how to do it of course. But I would really like to help people out in their Honda restorations. There are a few people out there selling information like this but that's just a little greedy in my opinion. If I did that I would maybe see 10 people actually pay for it and 5000 people would be out of luck.

This is basic mechanic skill that everyone should have. Anyone can take apart this engine and put it back together. As long as you can follow a few instructions and read a manual then you are good to go.

! ! ! IF YOU ARE GOING TO RIDE YOUR CLASSIC HONDA MAKE SURE AND ADJUST THE VALVES AT THE VERY LEAST ! ! ! It's SO EASY to adjust them!! Do this and adjust the cam chain tensioner and the bike will run smoothly and much better, not to mention more efficiently. Now for some pictures! - the cylinder head breather from the good engine is shown on the left along with a couple of the new valves and my favorite scraper tools (walnut picks I found at a garage sale for pennies =).

http://www.fourwheelperformance.com/honda/ca95_valves_01.jpg

Once you take off the valve caps you are right on top of the adjusters. A 9mm wrench, a feeler gauge and your fingers are all you need to get the job done if adjusting them is your goal. Loosen the retainer nut with the ol' wrench like so:

http://www.fourwheelperformance.com/honda/ca95_valves_02.jpg

The valves on this engine were so out adjustment I am amazed that it even ran for it's previous owner. The valves can only loosen and this just makes the valve open much later and close much earlier than they should. It doesn't hurt them but it just = much less power. Check these out! You can easily see the grossly large gap in this picture:

http://www.fourwheelperformance.com/honda/ca95_valves_04.jpg


Now when you adjust the valves they should be .004 on both intake and exhaust. It can be a tad looser but NOT tighter. When you actually see how tight this is you will understand. Loosen the retainer nut with your 9mm wrench and twist the adjuster down so that there is only a tiny gap and try and stick your gauge in there. The .004 is a tiny blade of a feeler so bend it in there and just try and get it so it barely will fit in there. This is all you need... then tighten the retainer nut pretty tight and check it again before you move on.

http://www.fourwheelperformance.com/honda/ca95_valves_03.jpg

Now if you have sharp eyes you will notice that I doubled up on the feeler gauges by accident! Look close at the gauge tool. The 004 size is so thin I didn't notice, at first, that it and the size before it were sticking together! This is VERY close and just lets air under where the rocker arm meets the valve stem. If the valves are too tight they will heat up and deformation will occur, "burned valves" being the result. With the rocker arm adjusted you can just lift up on it a tiny bit and barely lift it up and down. There is just enough space for air when you lift it with your finger. Here is what the gap should look like:

http://www.fourwheelperformance.com/honda/ca95_valves_05.jpg

[Smithers]

Of course I'm taking things a little further. I have new valves so I won't sleep if I don't replace them. First I wanted to see how bad the used valves really were and clean things up a bit.

http://www.fourwheelperformance.com/honda/ca95_valves_07.jpg

Get your favorite scraping tool out and poke all the carbon out as much as possible.

http://www.fourwheelperformance.com/honda/ca95_valves_08.jpg

Then take a rotating wire brush type tool to the combustion chamber and give it a good scrubbing. This literally took me 3 minutes. Gotta love air tools.

http://www.fourwheelperformance.com/honda/ca95_valves_09.jpg

Before being cleaned up here is what the exhaust valve looked like. This is extremely dirty because a previous mechanic (or person who fiddled with the engine) did a horrible job honing the cylinder during a rebuild and it was blowing by tons of oil as a result. After a while it probably ran so horribly that this was the reason it was retired to the garage. Here I can't even see the surface of the valve seat so this indicates that the valve seat is in very bad shape.

http://www.fourwheelperformance.com/honda/ca95_valves_10.jpg

The exhaust valve seats are so bad that there is no question they need to be lapped in or replaced. The intake seats are better but still need attention or replacing. Lapping them in and using them would be fine in this case but I'll be using my new ones thank you.

http://www.fourwheelperformance.com/honda/ca95_valves_11.jpg

http://www.fourwheelperformance.com/honda/ca95_valves_12.jpg

Here is a good shot of everything apart. In order to get them apart I highly recommend a valve spring compressor. I used some super high tech wrenches and was able to pop them out by hand but I've done this on different engines so I know what to expect. Please be safe and use a spring compressor (they can be had for $40). You don't want to break anything or lose any parts. Lose any of those tiny valve spring retainer keepers and you are doomed. I wouldn't want to find another one of those for sale.

Tomorrow I'll be taking the head to the engine shop for a dip in the clean tank and a professional inspection. In the meantime I need to find a valve spring compressor to install the new ones. If he's not too busy my engine builder might volunteer to throw it together for me when I ask to borrow his tools but we'll see what happens. :lol:

[Smithers]

I began a new thread of the steps I took to lap the new valves in as well as installing the springs and the rockers. This thread has been pretty dirty so far and focuses more on adjusting the Honda valves to insure proper duration. So (here (http://www.fourwheelforum.com/index.php?showtopic=163)) is the new thread starting fresh with a clean cylinder head and the nice shiny new Benly 150 valves.

In case you missed how much fun I had cleaning the head and between all the cooling fins of the Benly 150 here is the quicklink. quicklink. (http://www.fourwheelforum.com/index.php?showtopic=160)

[Griff]

Any tips on doing the left or right side first when at TDC or intake vs. exhaust first?

It seams when I adjust mine at TDC then spin the motor 360 degrees they're all either way too tight or loose again?

[djbrett]

The shop manual states .1mm gap. i've looked at a few of the different forums and they say .004 or something of the sort. is this a standard measurement, am I reading wrong...?
Also, from the forums, it appears that the spark fires at the same time on both cylinders (2 out of the four strokes), so, I adjust the left cylinder, rotate the points 360 degrees back to the T, and then the right, right?
This is only confusing to me because I thought I read somewhere that the 154 fires both cylinders simultaneously. Then again I've been wrong before.
Thanks,
Brett

[djbrett]

never mind. owners manual lists .1mm and .004 in. oops. that's why i'm a junior member:)

[Smithers]

Hey you need to learn sometime! Mind your measurements!!

[wnbasac]

Tks big time for taking the time to make a step by step illustration for people who are learning the craft like me
>
i have a spare engine that i'll practice on 1st so as not to screw up the one on the bike
>
still have a few questions

a. do you have to or should you replace the gaskets /seals on the valve caps

b. where is the mark located to rotate the engine to adjust each set of valves

c. how does one adjust the cam chain tensioner

once again Thank You very much for taking the TIME to help us newbies it is greatly appreciated
>
Have a Hondafull Day

[djbrett]

I'll answer and let the experts correct me.
a. never a bad idea to replace gaskets. I haven't yet, but want to pop out the old ones and put new ones in. They don't look special, so I am just gonna take one over to ace and try to find new ones.
b. I used the marks by the points. If you take off the cover over the points, there is a small window and line at about 1 o'clock. Line it up with the "t" and the valves should be up on one side and down on the other.
c. sorry, don't know, didn't do it. I know there are threads on it though.

[dickevins]

I'll answer and let the experts correct me.
a. never a bad idea to replace gaskets. I haven't yet, but want to pop out the old ones and put new ones in. They don't look special, so I am just gonna take one over to ace and try to find new ones.
b. I used the marks by the points. If you take off the cover over the points, there is a small window and line at about 1 o'clock. Line it up with the "t" and the valves should be up on one side and down on the other.
c. sorry, don't know, didn't do it. I know there are threads on it though.

This page is one of the reasons that this site is so phenomenal. Thank you experts for the good instructions and the very helpful photos.
de

[wnbasac]

djbrett thanks for your reply

theres one thing i love about this forum is that NO matter how simple or stupid the questions are that i ask, you guys make me feel very comfortable!

Thanks and have a Hondafull Day