Compression test on 2003 RX-1-QUESTION

[KbxSrx]

Has anyone done a compression test? What are you seeing for numbers?

 

[Skydog]

Its not the number, just make sure they are all close! Then you are good to go!! Better yet to a leak down test.

Skydog

 

[kinger]

Spec is 175-210 I think so its a huge range. My personal apex all stock was 150 across the board which I thought was very low but tore it apart and put a head shim in and Ulmer said its tip top so like sky dog said forget the number and make sure they are all within 5% of each other.

I do a CR and leak down every year. Leak down is a cool test but its a PITA to get every cylinder at top dead center take me at least 2 hours of messing around but at least I can monitor it season to season.

 

[rxrider]

I have a dial indicator that goes into the plug hole, finding TDC takes a few minutes at each cyl at the most, nice tool to have

Agree with the across the board readings beeing close, nothing to worry about unless one or more are way off the others (lower compression that is).

Leak down can be decieving as well. There is no need to have close to 0 leak down, you will make more power tho, but your engine is not shot if it's leaking some. Read it on a racing car tuning site some time ago. The engine builder did not worry before leak down got past 20%. His take was he could easily get the power and compression back with the use of higher boost.

 

[KbxSrx]

Thanks RXRIDER.

I am trying to find the correct compression tester, going to take another stab at it. I was using one that you just hold the rubber against the hole and crank, but doubt the reliability.

More info after I get more info.

 

[mulot30th]

Spec is 175-210 I think so its a huge range. My personal apex all stock was 150 across the board which I thought was very low but tore it apart and put a head shim in and Ulmer said its tip top so like sky dog said forget the number and make sure they are all within 5% of each other.

I do a CR and leak down every year. Leak down is a cool test but its a PITA to get every cylinder at top dead center take me at least 2 hours of messing around but at least I can monitor it season to season.

Funny.... I do leak down tests regularly on my sleds and take me like half an hour to do all 4 cylinders.


to me past 10% leak down I check the head... 905 of time problem lie int there...

if not, engine rebuild is required.

typically I get around 5% to 8% leak down on good running engines.

 

[KbxSrx]

where would I find a leak-down tester?

 

[Turk]

Tons of good cheap ones on e-bay ken.

 

[KbxSrx]

But it is such a tiny spark plug hole, do they come with that insert? The ones I have seen (comp testers) only have the small and large sizes, not the itty bitty yamahole

 

[mulot30th]

Mine did not came with (a good one at auto parts store) but I ordered that 10mm fitting beside

 

[givemeaboost]

You will need to get a 10mm adapter to fit the compression tester.

 

[GT Mills]

Here are my methods for a leak down test>

1. Never do a leak down test with piston at TDC, always do it at 15-20° BTC.
2. Don't get your panties in a bunch over getting the angle perfect. Stick a long, skinny rod (a clean wood dowel or bamboo Shish kabob sticks from the grocery store work great) down the spark plug hole, and rotate the engine until you reach see TDC on the wood plunger, then go back 15-20° BTC. Put a flag on the dowel with a piece of tape, that will get each cyl close enough to the same place each time.
3. You can do the leak down test on a cold engine if you must, but you will get much better results with a worm motor of course.
4. There's no such thing as a zero leak down test on a typical engine that has been broken it, 5% is about as good as it gets. 10% is an excellent engine, especially one that is boosted. If you are racing for $$$ you would tear it down at 15-20%, if you are a hobby racer don't waste your time/money on a tear down until after 25%.
5. If you crank up the boost to compensate for a compression leaks you are seriously screwing up your engine. That is terrible thing to do. If anything, you should be dialing it back, unless you don't give a rat's patootie about burning valves or eating up rings...
6. When setting the gauge knob go for the mid range of acceptable regulator flow on the dial.
7. If you get a bad cylinder, listen from where you hear the air to figure out what's wrong. Air heard though the throttle body side is leaking intake valve, air heard in exaust is leaking exh valve, air heard in the oil gallery is bad rings.
8. Lock the engine in position each time before pressurizing the cylinder.
9. If you get a bad cyl reading, run the engine for few minutes and try it again, sometimes a valve gets stuck open that will close after a running again.

 

[GT Mills]

I've done compression checks on numerous RX1's with anywhere between 400 - 10,000 miles on them. The extension hose to reach down into the spark plug hole seats with a rubber O Ring and I never tighten it beyond finger tight. On a cold engine, all plugs out and using the starter motor to crank it over I've never seen anything over 130 LBS on my gauge, more like 115 across the board one the one I am flying on my gyrocopter currently. But I think that the low numbers are due to my set up, because every engine I've checked this way runs like a champ, typical RX1 oil use, and all start up cold on first crank w/o choke if the engine has been run in the last few days, plus decent leak down numbers.