Low Compression CL350

fluke12

fluke12

Been Around the Block
I've posted a few times about different low compression questions, but I'm going to keep them together on this post from here on out.

Backstory, low compression (140 psi) in right cylinder, normal 170 in left. Top half of the engine is apart, head gasket SEEMS fine not sure what to look for when inspecting it.

Rings were intact and though they were a little bit outside standard (.2-.4mm, they were .53 and .6 and .45) they weren't to that magic replace me number of .8mm. I broke the oil ring trying to put it back (awesome!), so I have a new set on the way in addition to a set of full new gaskets. Peeling gaskets off has to be one of the most tedious, annoying parts of engine work.

I don't have a valve spring tool or a precision cylinder gauge, so those are my next points of attack?

My question
Should I go ahead and replace the rings that are just outside standard but not to the replace if over number or should I save them for later just in case?


Thanks for the help!
 
First: go back in time and find out why compression was low.

Did you adjust valves before you pulled the head?

You're going to want to hone the cylinders if you put new rings in. But - are they within spec?

If you're not sure whether the valves need work, you'll either be removing them now or hoping they're okay (because if they're not, the head comes back off).

There are a couple pretty good threads on HondaTwins detailing the valve removal and making a tool to do it.

Best luck man!
 
Before I pulled everything apart, I did adjust valve tappet clearance. Got them to where they should be before I did the compression test.

I've been troubleshooting and measuring based on easiest/tools I have on hand.

Rings are outside standard value but inside the replace number, so I wasn't sure if it was just safer to swap them all.

Piston diameter is right on where it should be.

Thanks for the tip about valve tool too, I'll look into that
 
No problem.

You'll want to go ahead and replace the rings if they're en route
 
i just use a socket and a hammer to remove valves
it is a tried and true method but you gotta be careful ;D
 
I went to harbor freight and got a cheap spring compressor. Wasn't sure how I'd get it all back together with a hammer. Right before leaving for a family vacation, I snuck out to the garage to try it out. It worked ok, still had to put a bit of pressure behind it because I couldn't grab low enough on the spring.

Anyways, here's a picture of what I found behind the valve (which basically slid out with no pressure, I'm gonna have to measure that). Looks like there is some carbon buildup on the valve seat.

What do you think the best way to clean this? One of the manuals talks about not using a wire brush with the valves off to keep from scratching, so something like carb dip/cleaner?

I'm assuming I'll have to do some lapping once everything is clean and measured.

Also, since I had good compression on the other side, should I pull the valves just to see if there could be an issue in the near future or not mess with a good thing?

dajy4eta.jpg



THANKS everyone for the help!
 
Yeah that valve seat is pretty crudded up. I would go ahead and clean that crap off with a wire brush and some acetone. Be careful not to scratch the seat too much. Then lap both of those seats in. Looks like that engine sat with a valve open for a while. What do the back sides of the valves look like? ARE the STEMS straight?

Once you have the valves lapped, put them back in correctly and stand the head on one set of its ports IE the front or the back side and pour some of that acetone down into the ports behind the valves. Acetone is very thin and will tell you if you have leaky valves or not as it will start to leak past the valves pretty quickly. If one side checks out, do the other. You can check the "good" side this way as well, if it doesn't leak leave it alone.

If everything seals, I would say that you had found your issue with the low compression. Put new rings in and run it.
 
Use a brass wire brush and you won't scratch the head
 
Sweet I used a brass wire attachment to clean the combustion chamber with the valves in and it did a great job with what looks to be no notable scoring at all.

Good idea on the acetone test, I tried the oil on the top and air through the ports and got no bubbles on any valves on either side.

I'll let you guys know how it all goes once I get back into town and I can give it a go.

I appreciate all the help, hopefully I can get it all back together correctly after I fix the problem.
 
So I finally got around to doing this after my vacation. Cleaned the valve seats and lapped them both.

I've never lapped valves before so hopefully i did enough without doing too much. Before I started, the exhaust valve was pretty dark but the intake was fairly clean and chrome shiny. After lapping them both they both had a satin finish.

I put them all back together and didn't have any acetone so I tried testing using seafoam. After about a minute or two, I got just a little hint of liquid, like just enough to see a shine on the exhaust side. That probably means I didn't do enough lapping right? Also did the same thing on the "good" cylinder too, it basically did the same thing. Does that mean that side needs some help too even though it had proper compression?
 
Usually, after lapping, it takes a bit of running to get a good seal. The satin finish will be worn down by metal-to-metal contact and the seal will improve.

That said, it is still very much preferable to have zero leakage.

If you have the money in your budget, take everything to a machinist for a valve job. If you don't have the money, you can always try assembling things and crossing your fingers.
 
Test I use to see if I have a good lapping job is to clean the seat and the valve well then color the valve seat with a sharpie marker and let it dry. Then spin the valve against the seat a few times and take it back out. If I have a good job I should have shiny metal all the way around, no gaps or overly thin spots. That at least will get you an idea of how much more you need to go. I bet if you would have tested it prior to an lapping that Seafoam would have just poured out.

You also need to make sure you don't a bent valve stem or burnt valves.

Second Matt's suggestion as well.
 
I didn't see any signs of a burnt valve, and the stem is straight, at least straight enough that when I lightly chuck it in a drill and give it a spin you see no wobble.

I watched a few YouTube videos of people lapping and they seem to spin it a lot longer than I do, I only spun for a minute or two basically until the grinding sound changed. They may be using more compound than i was. I'm gonna try the marker thing and see what's up with that. Maybe try lapping again and if that doesn't do it, I'll look into taking it some place. Trying to do what I can myself before i drop some cash.

Thanks for the advice. This time I'll take some pictures and post those.
 
I was using this

http://m.autozone.com/autozone-mobile/en/accessories/Permatex-Valve-grinding-compound/_/N-2592?id=526806

This stuff no good?
 
lap lap lap
you cant just lap and lap and lap worn out valves it is only for a minor touch up and final seating
you should check the seat width after you get a seal it must be within specs in the factory service manual
lapping seats makes them wider,it's pretty easy to go outside the spec
if the contact area on the seat becomes too wide then it is time to take it to a professional
if they have the right tooling they can narrow the seat
the other thing you need to do(and always do it FIRST) on an old motor is check the stems and guides
if they are out of spec, they are worn out, must be replaced
also valve stem stickup must be kept within a very narrow range
 
Hmmm... the stuff I usually use lists the grit numbers. I start with a rougher grind and progress to a medium. Some folks use the fine grit to finish, but I find it's usually not needed.
 
Any suggestions other than red lead or bluing to check my seat width? Theoretically the marker trick should remove only where there is contact, leaving me a spot to measure right?
 
Ok. Relapped and rechecked valves a few times and couldn't get a consistent stripe all the way around. Some spots the seat was a perfect 1mm some, it was not. Still holds the seafoam the same way as before. I have an email out to a local guy/one man shop to see if he can't help me inspect and fix the issue. I'm hoping at least this way I can learn something in the process if I have to end up paying for it.
 
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