205 lbs. compression?

[scdmarx]

On the left side I tested both cylinders, they were almost identical.
The right side I tested only #3.

Good idea, I'll try a running compression test.

Here are some notes taken from a training class a few years ago. I'm hopeing you will find it useful.

The volumetric efficiency test or running compression test
is a very good test to use any time you have a engine miss
that can't be traced to ignition or other basic systems or
when there is a lack of power.

Step 1. Preform a cranking compression test with all plugs
out and the throttle open.

Step 2. Record your cranking compression readings. Make
sure the charging system was up to snuff so all cylinders
were tested under the same conditions.

Step 3. Install all plugs but one. Install a standard
compression guage in the remaining hole with the shrader
valve in place.

Step 4. Start the engine. It will run but will be
missing on the cylinder with the compression guage. Burp
the guage and allow the reading to stabilize. It will be
bouncing around at about 50 to 60 psi. (the throttle is
causing a restriction and the piston is moving fast
compared to cranking speed causing only a partial fill of
the combustion chamber).

Step 5. Snap the throttle wide open and return to idle. The
guage will hold at the peak reading. This reading is higher
than idle because the peak comes at the instant the
throttle restriction is removed and the piston speed is
relatively slow.

Step 6. Record your readings for running snap compression
for all cylinders. The running compression reading should
be approx. 80% of cranking compression. (example: cranking
compression = 150psi running compression should = about
120psi)

If your running reading is below 80% of cranking
compression, the intake system is causing a restriction. If
the running reading is above 80% of cranking compression,
the exhaust system is causing a restriction. If the problem
is in one cylinder you either have a problem with a worn
camshaft, broken spring/rocker, carbon build up, etc. If
the problem is on all cylinders look for a restricted
intake system or clogged cat/muffler. The 80% spec is a
ballpark spec and should be used as such. Remember that
cranking compression is a measure of cylinder seal while
running compression is a measure of volumetric efficiency
or the cylinders ability to draw the air/fuel mixture into
the combustion chamber.

Also, is 205lbs. compression a bit higher than spec for this motor. My concern for asking this comes from reading a discussion in a car mechanics forum about some pistons with busted ring lands. This was a factory equipped turbo motor (Subaru with opposed 4 cylinder) and the general common opinion was that the owner of the car had modified the waste gate, or the waste gate system had somehow failed, resulting in excessive boost. The pistons could not handle the increased cylinder pressure.

If your GW motors compression is supposed to in the ball park of 175lbs compression, and you suddenly get 205lbs due to a camshaft swap, you might want to at least keep a close eye on detonation issues. Just pondering out loud. Maybe not even an issue in this case.

 

[dan filipi]

I'll redo the test blipping the throttle like it says.

 

[scdmarx]

The reading you're looking for is the wide open throttle "snap" when the compression guage maxes. That compared to the static compression readings. On all cylinders.

Step 5. Snap the throttle wide open and return to idle. The
guage will hold at the peak reading. This reading is higher
than idle because the peak comes at the instant the
throttle restriction is removed and the piston speed is
relatively slow.

 

[dan filipi]

The reading you're looking for is the wide open throttle "snap" when the compression guage maxes. That compared to the static compression readings. On all cylinders.

Step 5. Snap the throttle wide open and return to idle. The
guage will hold at the peak reading. This reading is higher
than idle because the peak comes at the instant the
throttle restriction is removed and the piston speed is
relatively slow.

I did this on all cylinders 4 times to verify the readings.

Left cylinders = 120
Right cylinders = 130

So..........

left side static compression being 160, 80% of that would be 128. 8lbs. off but close.

Right side static compression being 205, 80% of that would be 164. 30lbs. off, something screwy.


If your running reading is below 80% of cranking
compression, the intake system is causing a restriction.

If the problem is on all cylinders look for a restricted
intake system or clogged cat/muffler.

Since the 2 right cylinders are together into one exhaust could I be dealing with a clog in the exhaust causing the high static (200+) reading?
Maybe it's time to pull the exhaust and do this same test.

 

[scdmarx]

I did this on all cylinders 4 times to verify the readings.

Left cylinders = 120
Right cylinders = 130

So..........

left side static compression being 160, 80% of that would be 128. 8lbs. off but close.

Right side static compression being 205, 80% of that would be 164. 30lbs. off, something screwy.


If your running reading is below 80% of cranking
compression, the intake system is causing a restriction.

If the problem is on all cylinders look for a restricted
intake system or clogged cat/muffler.

Since the 2 right cylinders are together into one exhaust could I be dealing with a clog in the exhaust causing the high static (200+) reading?
Maybe it's time to pull the exhaust and do this same test.

May be the next logical step. Not a hard thing to do at this point. But remember also, the potential for restriction starts with the configuration of the cam lobes. Lift, duration, and the timing thereof "?" rocker arm ratio, port size, plugged pipes.

 

[MSGT-R]

And don't do it early in the morning 'cuz it's gonna be noisy! :roll:

 

[scdmarx]

Y'know, I still not totally convinced this is not a cam timing issue.

 

[dan filipi]

Y'know, I still not totally convinced this is not a cam timing issue.

Yeah, I don't think it's restricted exhaust because this showed up right after the 1200 cam went in and went away with an 1100 cam in it's place then returned again with the 1200 cam.

 

[MSGT-R]

But one would assume that it would be the same left-to-right.

 

[slabghost]

But one would assume that it would be the same left-to-right.

A lot of variables in this. So much has been done recently and Lord only knows what was done by previous owners. The test results though a little mixed show a pretty healthy build. I think it high time to put some miles on it for a season and see how it shakes down. All these changes need some time working together to realize the full impact of the mix. :good:

 

[MSGT-R]

Well, like I told Dan on the phone, if the differences in running compression aren't too great, the uneven pulses will be taken up by the flywheel inertia. When they become too great, you will feel/hear it in the idle, and increased vibration under load.

 

[slabghost]

Well, like I told Dan on the phone, if the differences in running compression aren't too great, the uneven pulses will be taken up by the flywheel inertia. When they become too great, you will feel/hear it in the idle, and increased vibration under load.

That is a good point but I don't recall any such vibration being reported. Only tappet noise which has lessened after resetting the valves I understand. The difference from side to side is perplexing but the firing order side to side negates a lot of the possible vibration along with flywheel inertia.

 

[dan filipi]

Agreed, I wish I had a way to check the valve timing other than the usual marks in the proper alignment.

 

[mcgovern61]

Sooooo.....any conclusion? :read:

 

[joedrum]

well anybody thats had one cylinder dead knows that they will run like that but there is a noticable vibration there from the bang process ....when the piston gose bang it is out of balance period ...flat fours do reduce that better than most motors but its there ...only radial motors have almost no vibration from design of motor ....on two cylinder a oldwing can sound like its going to explode :shock: :hihihi: :mrgreen: :rant: :nea:

 

[Sidewinder]

So, what happened? Like reading a mystery novel to find the last few pages are missing. opcorn:

 

[dan filipi]

So, what happened? Like reading a mystery novel to find the last few pages are missing. opcorn:

I never figured out why I was getting 205 compression.
I recent test shows it down to 190, still high and yes the mystery continues.

 

[mcgovern61]

Man.....what a tease! I thought there was new information! Kinda like me opening up that '81 and splitting it......soon.....I hope...... :lazy:

 

[westgl]

I like this thread, and really enjoyed seeing that the power/torque came in earlier in the rev range.

You have probably already done some engine conditioning to this engine prior.

Run ATF/Oil mix to help clean the rings, and other internals.

Seems funny that it appears to be wearing in as time goes by.

I say this because, If the Valves were, Cleaned & lapped, it sounds like it is loosing compression some where, because of the difference.

Maybe it just a matter of running it enough, another 10k and the comp. from side to side should match by then.

I never have a problem with more riding.

 

[MSGT-R]

Well, my bench-testing has come to an end with the demise of my 1100.

On 21 April, an inatentive driver turned left in front of me (less than two seconds) in a 40 mph business district on an empty street. He totaled my wing and sent me to the hospital. I am now out of my cast and doing the rehab-thing. I'm now sporting 9 screws and a plate in my left ankle and have reduced mobility (that I'm working on).

The wing is gone and I don't know if there will ever be another. I have two other Hondas to ride, but there will be no riding until I can walk again on my own and build up some strength. I was wearing all the gear (like I always do), so the ankle is my only serious injury. The rest was brusing and muscle strains.