Compression Check
- Thread starter Torque addict
- Start date
warp9.9
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A bad ring can very well cause this as well as a damaged piston which is pinching the ring. If this has happened no amount of oil will correct the seal. (don't ask me how I know
)
You also can blow head gasket and make pressure in areas you would never think but then you have a turbine creating higher cylinder pressures in the first place I suppose you can just pressurize the crank case with a bad head gasket but you have a higher probability of pressurizing the water jacket.
The good thing about a leak down detector is you will be able to isolate the problem better. A good scope can also tell you a lot if you take a peek down the spark plug hole.
Say for lack of better understanding you want to check and see how hard you hit your pistons with the valves?
A good scope can give you a idea
again do not ask me how I know !!!!!!!!!!!!!!!!!!!!
)You also can blow head gasket and make pressure in areas you would never think but then you have a turbine creating higher cylinder pressures in the first place I suppose you can just pressurize the crank case with a bad head gasket but you have a higher probability of pressurizing the water jacket.
The good thing about a leak down detector is you will be able to isolate the problem better. A good scope can also tell you a lot if you take a peek down the spark plug hole.
Say for lack of better understanding you want to check and see how hard you hit your pistons with the valves?
A good scope can give you a idea
again do not ask me how I know !!!!!!!!!!!!!!!!!!!!
cusso ken
Living Legend
VCT engines do alter the Compression Ratio I would have not heard that the R3 has VCT but may be wrong
No Variable Cam Timing on the Rocket.... the reference would have been to VARIED (altered) cam timing.... i.e., hot-up stuff.........
cusso ken
Living Legend
Thanks mate the Rocket motor is still a bit of the unknown for me,
Neville Lush
www.nevillelushracing.com
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Stock CRANKING PRESSURE on a R3 is 210psi. (sorry Ken ) Even with the lowley 8.7 comp ratio. If your engine is turbocharged and still is stock internally, then your cranking pressure should still be stock ie 210 psi. Assuming a) good gauge, b) proper technique then your comp is all over the shop. Has your turbo been tuned properly? most likely cause is melted pistons/rings from poor tune causing blow by etc.
cusso ken
Living Legend
Thanks Nev I was only going on the "old " yardsticks of mild compression engines ,even a stock 351 ci ford V8 is under 190psi, the 460ci ford engine in my F100 , I built for running on LPG with Gas Cam and hardened valves ,with the distributor recalibrated for LPG ie high early advance and tapering off up high running 10to1 compression only registers 200psi at cranking speed . interesting figures on the R3
Neville Lush
www.nevillelushracing.com
- Joined
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- Victor Harbor South Australia
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- Speed Triple 1050 Dirt Track sidecar,H2750Roadrace sidecar W800 Kawasaki
cranking pressure and compression ratio are two different things Ken. The R3 is a low compression engine, with high cranking pressure. A Ford is, well.....a Ford. 200psi sounds about right for your big one on LPG. 10:1 is not that high although high maybe for that motor. A new KTM 250 mx bike has 14:1 stock. Many variables.
Torque addict
Supercharged
Very good. Thank you! Now that's a response I can believe and also matches what both Scott and ruzzle have said. I will be bringing home a very expensive Fluke pressure calibrator from work and hook that up to the hose on this el cheapo tester I bought (in place of the gauge it came with) to get the real story. Don't know why I didn't think of that in the first place. I suppose there's still a chance the O-ring on the fitting isn't sealing perfectly but my results were consistent with multiple checks. I repeated 3 times - cylinder 1, 2, 3... 1, 2, 3... 1, 2, 3 seating the O ring firmly each time.
However, I've already decided I'm ripping it apart. I did a partial leak down test this afternoon. Did not have the gauge set up to see percent of leakage but simply set the regulator on my air compressor to about 30 psi, removed the check valve from the end of the compression tester hose and blew air into each cylinder with piston at TDC on compression stroke. Took radiator cap off and removed the hose from the crank case vent at my catch can. Visually looked for bubbles in the radiator and listened at throttle bodies, exhaust pipe and crank case vent hose.
Cylinder #1 - Immediately heard air coming out of crank case vent hose and felt it on my arm. It was moving my arm hairs from a few inches away! No indication of air at the other check points.
Cylinder #2 - Very quietly heard air from the crank case vent hose. Could not feel it unless I plugged the hose for a few seconds and then released to let the air escape. No indication of air at the other check points.
Cylinder #3 - The bike immediately started to move forward since it was in gear as rocking it forward was how I turned the engine with a long screwdriver in the hole resting on the piston to see when it stopped rising. Same pressure as the other two cylinders, in gear for each test. No need to even check for leakage after that but I lowered the pressure until the bike didn't move forward. Just a very slight hiss from the vent hose.
So that's enough confirmation for me, it's coming apart. I guess the readings I get with the Fluke calibrator will help me decide if I'll be dealing with 1 piston or 3 and of course what I see visually when I get it apart. This will be the first time I've gone this deep into a motor but with the wealth of knowledge and helpful advice found here on this great forum I feel very confident.
And yes, the previous owner had the bike tuned properly by a knowledgeable tuner but the guy who owned it before him blew a head gasket and replaced it himself. My guess is that's when this damage was done. Maybe it has slowly gotten worse over the last 2k miles it's been ridden. When it was on the dyno they noted that the intake plenum was filling up with oil (listed that way on the receipt he gave me). So the guy I bought it from purchased the catch can but decided to sell it before he installed it. The bike certainly has no lack of power. Can't wait to see what it does with all 3 cylinders at full compression!
cusso ken
Living Legend
Thanks again Nev,goes to show you are never too old to learn ,I am only a bush mechanic that picked up a basic knowledge from my Father and through roadside repairs on my trucks and workshop tinkering,
