How much compression do you have with standard head and RockSolidEngines Billet Head

210061741 said:

I love it.

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So do I. After a second ride, same opinion. Starts better, idles better, a bit more power all through the rev range. The engine seems to like it, like it should have been standard.
Also, RSE's billet head is much meatier than the stock head, with roughly double thickness fins etc.

Hello Clay, I read the threads on your mods with interest, a couple of weeks ago. Good job. Be interested to see how mine and Fabian's compressions compare with yours.

Fabian, I didn't get a chance to look for a screw-in comp gauge today. Had to catch up on a few chores. Tomorrow.

... Steve

Here's mountain80's stock compression. (Not sure about the 160psi, though. If the only mod was 50 thou off the head, that sounds high.):-

Thread Title: Compression Numbers

mountain80 said:

So I thought I would check around on what everyone is getting for compression numbers on their modded HT. I was getting 95psi stock at 4000 feet altitude and with the work i've done it is at 160psi. Its been like that for over 3000 kms now and no problems. I did port and polish and match as well as taper bore the carb and took 0.050 off the head. I also changed out the needle bearing to one out of a stihl chainsaw for better reliability. Any ideas how far we can go before she pops the rod????(Yah I know just before she pops the rod lol)

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... Steve

Sorry to hog the thread. Got a screw-in tester today. (SuperCheapAuto, Product #12556, $45AU)
Result: 135psi with RSE billet head.
Tested twice, WOT, normal starting speed.
A bit of extra advice. CDI units don't like being charged without firing. When doing tests of this sort, it's a good idea to stick a plug in the cap and hang it on the head to allow the CDI to discharge. They can otherwise build up higher than normal voltages and fail (prematurely).
... Steve

Ok,

I've done a compression test on my Rock Solid Engine with Billet Cylinder Head.
The compression does not seem to have changed (either increased or decreased from brand new) since i've installed it in my bike.

I've done approx 80 kilometers of distance on the engine.
I'm getting a repeatable 90 PSI or 600 Kpa from a high quality, professional grade, compression gauge.

How much compression does a standard, non angled plug, cylinder head have on a 70cc engine - very curious to know the figure.

Fabian

You're kidding? Only 90psi? That sounds pretty low to me. Are you sure the gauge isn't sticking or something? (Even 'high quality, professional grade, compression gauge's can be faulty.)
My new gauge is only a cheapie at $45, but I doubt if the error could be 45psi.
Mine's a stock, (except for the billet head), new series ZBox 66cc, did 290km before fitting the new head and about 20km after, before the comp. test.
Have you talked compression with Tony Ciccio at RSE?
... Steve

Tony is aware of my situation and is in the process of sending me another cylinder and a set of piston rings.
He went as far as saying that he would refund my money and also pay for the postage costs, and then run the engine to it's limits on his dyno to find out if and why there might be a problem.

For some unknown reason my engine is seriously down on compression, despite the leak-down test on my engine being perfect when it left his factory.

It's quite strange as his other customers have reported a significant increase in compression and power, which would stand to reason.
My engine just isn't doing what it should be doing and yet, i know that it should be doing quite a bit more than what it's doing.

Fabian

As i have a SickBikeParts shift kit, it's a pain, to keep changing over engines and the quality of castings of the Rock Solid Engine are much better than the standard Chinese engine as is the sealing method of magneto wires exiting the engine.
The quality of chrome on the cylinder bore is also much better on the Rock Solid Engine, not to mention a quality set of bearings installed in the engine.

In saying that, it's easier for me to keep the engine in the frame.
Tony is sending me another cylinder and a set of piston rings.

I knew something wasn't right as the bike didn't seem to have any more compression than a standard engine, from the first test run.

We compared compression gauges by using another gauge from an auto repair shop a few doors down.
90 PSI is all i'm getting.

I am still confident that everything will work out well as Tony stands behind his product and services.

Fabian

Out of sheer curiosity, I'll bolt the stock, (unmodified), head back on tomorrow and do the same test, for comparison with the billet head's compression. I have a spare head gasket sitting here doing nothing.

Another thought, Fabian. Are you running the recommended oil ratio or somewhere near it? These engine's need a lot to seal well, I'm told. I'm still running 16:1 for now.

... Steve

20:1 is what i'm using with 98 octane fuel

Hey Aussie steve....Yes it is 160 psi with 50 thou off the head, im an ex motorcycle mechanic among other things and the smaller the combustion chamber the more psi you get when shaving the head. The intake timing and duration has been changed and the pressure was checked with proffesional tools NOT backyard mechanic quality.