Compression Question

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Compression Question - 8/27/2008 6:16:57 PM

stinemonster

Posts: 81
Joined: 7/26/2008
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Just bought a compression test gauge and checked the compression on my bike. I just got the bike back together after changing out the head gasket.

The compression read from left to right...

150/138/140/150 (psi)

The motor has about 46000 miles on it.

I only removed one plug at a time for the testing.

I have not been able to ride it yet because there is a tapping/knocking coming from the valve cover when it''''s running that gets louder as you throttle it up.

There is NO smoke or obvious signs of missing while running.

Do these compression numbers sound bad. The Clymer Manual calls the spec to be 185 psi +/- 28 psi.

< Message edited by stinemonster -- 8/27/2008 6:45:43 PM >

Post #: 1

RE: Compression Question - 8/27/2008 8:26:41 PM

Hurricane rider

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Joined: 8/23/2008
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They are all fairly close, and I''d say that 138 ought to be enough to run on, although it isnt ideal compression, so you''re not making the absolute best power you could. the middle cylinders may have a leaky valve seat, or something of that nature causing the slightly lower compression numbers. but 46k miles isnt brand new either, so its just regular wear/tear.

a tapping or knocking? does this sound change with engine speed? or no? it could be any number of things, but my money is on a cam bearing going bad on you, or maybe a valve that is seriously out of whack.

(in reply to stinemonster)

Post #: 2

RE: Compression Question - 8/27/2008 8:42:38 PM

stinemonster

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Quote "a tapping or knocking? does this sound change with engine speed? or no?"

Yes. It gets louder. It almost sounds like something is hitting something. It wasn''t there before I blew the head gasket. It''s about like the CCT noise when it''s at it''s worst.

The head gasket blew on one of the inside cylinders (#2 or #4 firing order). Can''t remember for sure right now which one but it was close to the inside.

I did peg the temp gauge bad when it blew. Supprised I didn''t loose the whole bottom end.

The cam bearing going bad? That would mean changing out the head and or the brackets that hold the cams in. Right?

(in reply to Hurricane rider)

Post #: 3

RE: Compression Question - 8/28/2008 9:59:45 AM

Hurricane rider

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Joined: 8/23/2008
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if the cam bearings are going, you have to replace the whole cylinder head, cam caps included.

did you by chance get the head machined before reinstalling? that would account for the discrepancy in compression if you didnt.

(in reply to stinemonster)

Post #: 4

RE: Compression Question - 8/28/2008 10:31:26 AM

stinemonster

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Joined: 7/26/2008
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I didn''t get the head machined. I checked to make sure it was not warped. It was in spec so didn''t want to spend the extra money not knowing if I did more damage to the motor from over heating it.

When I''m just turning the motor over, I don''t hear the tapping noise. I only hear it when it''s running and when the valve cover is on.

I''ve got the valve cover off right now, have started it several times and can not hear the noise.

I''m going to check the valve clearance. Maybe I can find something there.

(in reply to Hurricane rider)

Post #: 5

RE: Compression Question - 8/28/2008 10:37:41 AM

Hurricane rider

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Joined: 8/23/2008
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can you perhaps post a video of the sound and its location? that would help greatly.

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RE: Compression Question - 8/28/2008 11:15:46 AM

stinemonster

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Joined: 7/26/2008
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I dont have a video camera and I can''t tell where its coming from. I may could use my phone to get a short clip but not sure of how the quality will be.

Its not very noticeable with the valve cover off. Once I check the valve clearance I will reinstall everything and try to get a clip of the noise while its running. It sounds a lot like the CCT but tightened it up and it did not go away.

I will double check the torque on all the cam caps. Maybe I missed one.

Im going to have to wait for the motor to cool back off before I get back out there. I kept running it for short periods of time trying to track down the noise. I have an oil mess to clean up now.

I even tried using a cheap automotive stethoscope. I placed the rod straight onto the cam caps and could not tell any difference between any of them.

One thing I did notice was I didnt tighten the center screw that holds the breather base on but I cant imagine it making that much noise.

(in reply to Hurricane rider)

Post #: 7

RE: Compression Question - 8/28/2008 11:23:51 AM

Hurricane rider

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my money is on a cam bearing being toast. pull the caps, and if they''re anything but mirror finish shiny, you''ve got a bearing problem.

(in reply to stinemonster)

Post #: 8

RE: Compression Question - 8/28/2008 11:31:38 AM

stinemonster

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Joined: 7/26/2008
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Im looking at a new head and cap assembly right now and their running about $1000. I paid $1200 for the bike about 3-4 months ago and now have already sunk several hundred more into it. If I buy a used motor Im taking a chance of it being bad too. Know of a cheap place to order a head and caps?

Im going to try adjusting the valve clearance and hope thats all it is. After I get it back together and the sound is still there, I can get a recording of it then.

Somebody who is good at welding aluminum could make a killing at repairing these head and cap assemblies.

Will check the caps while I have the cover off.

< Message edited by stinemonster -- 8/28/2008 11:32:16 AM >

(in reply to Hurricane rider)

Post #: 9

RE: Compression Question - 8/28/2008 1:41:44 PM

Gearloose

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Joined: 9/12/2007
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I agree with everything Hurricane Rider has said.

In case it helps: regarding the compression pressures themselves, they may be better than you think because:
1. Compressions should be measured with all the plugs out - it looks to me like you took them out one at a time.
2. The adaptor you screw into the head can make a big difference to the reading, if it leaves some dead space that the genuine Honda compression tester doesn''t. The adaptor I use drops the measured pressure by about 10%.

Hope you get the tapping noise sorted. My experience with these engines is that even a small excesss of valve clearance (like 1/4 turn out) causes a lot of extra noise, but it should be more obvious when the cover is off.

The cam caps can be tricky- someone broke the cap on one engine I have by tightening the hold-down bolts out of sequence. Will keep monitoring your posts in case you draw a blank on the cap wear.

(in reply to stinemonster)

Post #: 10

RE: Compression Question - 8/28/2008 1:44:53 PM

stinemonster

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Hurricane Rider...

Why do you think its the cam bearings? Have you had this problem before?

I didnt look real close at the caps when I pulled them the first time. I just pulled the caps off and they are scored. Not just one, but all 3 that I have pulled. I would say they have about a 32 RMS. I would expect to see between a 16 and an 8 RMS. Do you think this is from the head gasket going and the bike overheating real bad? Or do you think this could be an assembly error? The last time it overheated, it didnt sound good. If this is an assmebly error, its an expensive one.

I already have so much money invested into this thing I have to fix it. I knew I was taking a chance purchasing a used bike with this many miles and this old. I was looking to spend between $2000-$3000 for a bike to get me to and from work. By the time its all said and done I will probably have about $3000-$4000 invested into this thing and a lot of time. The good thing is, for that price I will have an almost new bike.

If I had have purchased a newer bike for $3000 I still may be doing the same thing right now. I may never purchase a used bike again. Was planning on buying a new one next year but now may not if I have to sink a lot of money off into this one.

If I have to replace the head with a new head, I''''m going to pull the motor out of the bike and rebuild the whole thing.

At least its the first year the CBRs came out. Its a collectors item if I get it running or a shot up boat anchor if I dont.

< Message edited by stinemonster -- 8/28/2008 1:53:28 PM >

(in reply to Hurricane rider)

Post #: 11

RE: Compression Question - 8/28/2008 1:56:59 PM

stinemonster

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Gearloose...

Thanks. Along with adjusting the valve clearance, I''m going to try reassembling it with some better assembly grease and hope the tapping/knocking goes away. Should know here in a few hours unless I get frustrated with this thing and put it off until this weekend. Been sick the last few days so havent been to work. Will be going back tomorrow.

(in reply to Gearloose)

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RE: Compression Question - 8/28/2008 2:00:27 PM

stinemonster

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Joined: 7/26/2008
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servicehonda.com

New cams: about $400 for both

New Head and caps assembly: $875

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Post #: 13

RE: Compression Question - 8/28/2008 2:08:33 PM

Hurricane rider

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it may just be time to cut your losses and find another bike. Personally, when I''ve sunk more money into a bike in repairs than I have to purchase it, and this is for ANY vehicle, that vehicle is then parked and either sold or parted out and replaced.

this is just me though.

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Post #: 14

RE: Compression Question - 8/28/2008 2:26:11 PM

stinemonster

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This is why I stopped buying used cars. Got tired of working on them.

Have you burned the cam bearings before?

(in reply to Hurricane rider)

Post #: 15