Topic: Top end rebuild- was not expecting that

[rotortiller]

The place of the check valve doesn't matter, the moment that valve is pushed open the volume/pressure is the same for the whole compression tester system.

Yea it does, each compression stroke adds more air molecules to be stored and isolated into the hose by the check valve at the spark plug hole. If the check valve is at the other end of the hose next to the gauge then pressure does not get stored in the line emptying after the compression stroke. The hose design with the check valve near the spark plug end has become a charged pressure accumulator. Each time you kick the engine over through compression this line is charged a bit more until it reaches what is supplied by the spark plug tap. Very little differential pressure is needed to open the valve if someone wants to pick at straws.

Another way to ponder the situation like 'fizzlebottom' says. One situation has increased the combustion chamber volume (lowering compression ratio) while the other situation has not. Hope this helps you out.

[scottly]

+2...just run it.  Trying to put these together as good as Honda did is very expensive and difficult.

+3

+4 Run it!

+5


Sent from my iPhone using Tapatalk

It appears that Dime is determined to rebuild the top end, whether it needs it or not. I did notice that oldfart was viewing this thread, and, having read his rants regarding compression tests, have to wonder if he hasn't influenced Dime's decision making??

[willbird]

I get 150psi on a stock K7 engine kicking it over with the throttle open. You want a test gauge with the check valve in the spark plug end of the hose fitting otherwise you have altered the compression ratio substantially and should expect lower readings. Not so much hose length as it is test equipment design.

Sorry, I don't agree.
The place of the check valve doesn't matter, the moment that valve is pushed open the volume/pressure is the same for the whole compression tester system.

I picture it this way.
A high pressure bicycle tire pump fastened right to the presta valve on the bicycle tube and tire, each pump stroke fills the hose on the tire pump until the pressure is higher than what is in the tube, so that the pressure in the tube increases.

A high pressure bicycle tire pump that is fastened to 15 feet of 3/8 air hose, and then fastened to the presta valve on the tire and tube. Each pump stroke must pressurize the 15' of 3/8 air hose in hope that the pressure rises higher than what is in the tube, IMHO it probably never will do so, the pump does not have enough volume.

Same with the motorcycle cylinder, if we artificially add cc's to the combustion chamber at TDC the pressure will be lower. Adding a 12" of hose and THEN a check valve does add volume, that volume must be pressurized each compression stroke.

[PeWe]

Valve lash is OK when it should?
If cam chain is a tooth off.
New rebuild with bigger pistons should have higher compression.

My K2 got CI 392 pistons, +0.50mm. (61.50mm)
Compression tester showed +17OPSI on all.
They replaced K stock type CI 61mm. 150-160PSI with those.
K7/K8 cam.

[seanbarney41]

Does someone not have a couple different compression gauges around that are constructed according to what is being questioned here?   Would just take a few minutes doing a couple tests on the same engine so we can put this question to bed.  Post the results.  Hell someone probably already has with pics and video.  How about a link.

[rotortiller]

with pics and video.

Will not matter lol.