Is my motor healthy enough to mill the heads?

[jdewaard]

I have a 2000 Merc 225 Pro Max that I am considering having the heads milled. I just did a compression and leakdown test and here are the results. CYL 1 - 120 psi 10% leakdown, CYL 2 - 122 psi 10% leakdown, CYL 3 - 122 psi 8% leakdown, CYL 4 - 124 psi 10% leakdown, CYL 5 - 121 psi 10% leakdown, and CYL 6 - 122 psi 7% leakdown. All test performed with motor warmed up. Leakdown gauge used is Lang CLT2PB. http://www.eppys.com/ProductDetail.aspx?ProdID=3772

Are these leakage numbers to high? Is this motor healthy enough to mill the heads? I already run 93 octane premium and pre-mix 40:1 with Pennzoil XLF oil. Thanks.

[kingsbiship]

10% leakdown when warm is borderline! Raising the compression...
you mite be asking for trouble with your old rings.

[jdewaard]

Thanks kingsbiship......I was worried about that. I find it so hard to believe that this motor has such high leakdown. It only has about 175 - 200 hours. I am wondering if the leakdown gauge I bought is really accurate. What are good leakdown numbers? At what point do I consider re-ringing it?

[rev.ronnie]

10% leakdown is the recommend service indicator. Hours don't mean as much as leakdwon and there are factors like, usage (rpm range), type of oil used and general operating conditions.

I have a 260 that has 80 hours and less than 3% leak...some are far gone by then.

If your motor is stock, those leakdwon numbers and compression readings don't jive to me. I find it hard to believe that motor would have 135 plus when it's stock.

Its probably in better shape than you think. Try another gauge.

[rev.ronnie]

I just looked at that gauge. Looks like China to me. I like two of the same gauge and I'll do the math myself. That gauge you have looks like the Ching chong pos I had too...it wasn't accurate for crap.

[jdewaard]

The motor is stock except for the oil injection being removed. I am not as concerned about the compression as I am the leakdown. I am wondering how accurate the gauge I bought is? I have read that some gauges can be off by quite alot.

[jdewaard]

rev.ronnie, can you recommend a good accurate gauge? What if I changed the gauges to two of the same, higher quality kind or is the problem in the main body itself?

This one looks more like mine. http://www.langtools.com/65140.html

[Dave Strong]

10% on a steel motor is not as bad as on a NIC motor, still getting up there. No need to run 93 on that motor as was built to run 89.
Still as was said need to do tests with a known good accurate gauge. Can always pull the heads and look at the cyl's, and use a bore gauge if they are out of round or tapered with the piston at BDC then you know its bad.


Dave

[rev.ronnie]

rev.ronnie, can you recommend a good accurate gauge? What if I changed the gauges to two of the same, higher quality kind or is the problem in the main body itself?

This one looks more like mine. http://www.langtools.com/65140.html

I had a crappy one too. I just put two good quality pressure guages on it, Miltons if I remember correctly. If you adjust the pressure to 100 on the pressure side, the reading on the second gauge will be the direct percentage of that. 95 psi is 5% leak, and so on.

You can test at higher pressures too, just devide the holding pressure by the testing pressure and that will give you the holding percentage.

[Liberator*21]

When it comes to compression and leak down gauges........you get what you pay for. These are 2 measurements that I'd always recommend a top quality/professional style gauge, after all your basing the readings on the motors health. With a poor gauge you may end up with making a decision to rebuild when in all reality, it wasn't needed because a poor gauge wasn't reading right.

[jdewaard]

Well guys here is the latest. I purchased a new Milton (made in USA) compression gauge, more accurate and a couple high quality Weiss pressure gauges for my leakdown tester. I did a compression test with the new gauge and this is what I got. CYL 1 - 130, CYL 2 - 131, CYL 3 - 134, CYL 4 - 135, CYL 5 - 130, CYL 6 - 131. These number were read on a cold engine, I didn't have time to warm it up first, but am I right when I assume the compression numbers should rise when the engine is at operating temp because the tolerances become a little tighter because of expansion? I haven't done the leakdown with the new gauges yet because i have to get a couple fittings to adapt them over to the right size thread. I will be doing that this week and I will do that warmed up, as well as another compression test. I took a look in the cylinders with a AC Delco bore camera and all looks good. I can still see the faint cross hatch pattern on the cylinder walls and no gouging or scoring is present. I did notice that the domes of the pistons are black with carbon build up. I am surprised by this because I run 1 ounce of Sea Foam to every gallon of gas I burn all season. I would have thought that this would prevent the carbon. Should I do a de-carbonize? What is the best way to do this? What effect does the carbon build up have? Thanks.

[4JawChuck]

An easy way to check your tester is too deadhead it with a shutoff valve where the hose connects to the cylinder, good quality testers have a shutoff which makes this easy. This way you can check the gauges to each other to ensure they both read the same pressure.

If it was my engine I would just do it, stock engines are rarely better than 5% anyway, unless you custom rebuild the engine with a plateau hone finish, tight ring gaps with matched pistons to each bore to get equal clearances your not going to get an honest 3%.

For giggles do your lawn mower engine with your tester, you would be lucky to get 10% on that aircooled engine as it needs to be good and hot to get a good reading and even then they are so loose they don't leak down well.

The real point of this exercise (you did read the manual that came with your tester!) is an even reading across all the cylinders which is an indication of health...the actual reading is not that important unless your racing and want that last 2%.

BTW if your interested in building your own high quality tester the orifice size is 0.040" X 1/4" long with an entry angle of 60 degrees, all you need is two high quality gauges and a manifold plus shut off and good quality regulator...the hard part is the hose and adapters for the plug end which is easy to fab from an old spark plug. Test pressure is supposed to be 60-80 psi, these are all FAA specs for aircraft engine testing...max leak down is 25% before it is considered too worn out to fly.

Make sure your at TDC on a hot engine! :cheers: