Leak down test, what are good numbers?
 

I'm looking at a 500 HP carb, and the results of a cold leak down (boat was winterized, so was done cold)

and the results were between 8% and 18%. Nothing leaked into exhaust or intake. Leakage was rings.

What should this motor read?

At what point is it "bad" or just normal wear?

And are these numbers good, o.k. or screaming rebuild!

I would say OK.

8% is good, 18% is not very good.
It could easily be from the cold leakdown test also.

Hi Griff, thanks for the input.

I'll also ask for a hot compression test. And if they are good, is there any reason to do a leakdown test?

And if the hot leak down test numbers still are bad, what sort of money (ball park) does it cost the "freashen" a 500 HP ? (I see the term freshen, I assume that mean rebuild, or is that just rings and reseated valves, I'm not sure)

If this motor will need to be rebuilt, I don't mind that, as long as the price is lowered to make up for the repair. (would prefer factory stock, but on a 12 year old boat, I would assume that might be asking too much??)

If they my engines and they came in between 8 and 18 cold......I would consider them good. If you are considering a boat purchase, get the warm/hot numbers to have as a baseline.

Good.

How many hours on the engine????

Most likely, it would just need a top end refresh with a valve job and head gaskets. That should run less than 2k total with parts and labor.

Is there much of a diffrence between cold and hot test results ? is # 7 the common bad cylinder ?

You will see higher numbers when cold. The pistons should expand when hot and help seal. But if the valves are leaking, then it really shoudnt matter to much cold or hot I believe.

I did a cold leakdown test myself last year on my engines. No leakage from valves, all was into crankcase. Engines run great. Leakage highest numbers were around 14% percent on a couple cylinders, most below or around 10% cold. Blower motors with about 90 hours on them.

Leakdown tests are good to do, along with either a oil analysis or checking oil pressure after a hard run. If at idle, the hot oil psi is below 20psi, I'd be worried about excessive bearing wear.

Good point to remember about hot oil pressure , is there any method of checking bearing wear with motors in boat ?

Fixx
 

You will have to pull the engines in order to check the bearing clearances..i have a rod bearing tools that i use to check the clearances,the bearings could look good but the rods could be out of round,that's why i use the tool..

Found a great link on Leak Down test's

http://www.carcraft.com/techarticles...er/index1.html

Not that I plan on doing one myself, but still interesting article.

is number 7 the common bad cylinder ?

Does a compression test tell you the same thing as a leak down? If not then please educate.

Fixx
 

Compression test gives you what the cylinders will build in pressure,,a lead down test will tell you the condition of the rings and if the valves are sealing properly..

what is the minimum amount of air pressure that should be used for a leak down ?

Use 100 psi.....it makes the math really easy! :D

does less pressure say 32 psi not provide sufficient results

u r gunna need a bigger air compressor :party-smiley-004:

You got a bicycle tire pump your using?

Im looking at buying another boat and the guy did a leak down using 32 psi ..my mechanic will do a 100 constant pressure ..just looking for opionions

Most leakdown test machines will have the allowable input pressure range marked on them.

Tip: Make sure that the cylinder being tested is absolutely right on TDC, and that you remove whatever tool you are using to turn the engine over before applying pressure. If you fail to do both, well.... :eek:

Compression test numbers?
 

I know the rule of thumb is within 10% range, but what sort of LB's should it be?

What's a fresh 500HP #'s?
When did you rebuild your 500HP #'s?

If they are 150 LB's, I assume that is good.
100 LB's bad...I assume.

So what numbers are exceptable? and what numbers are, on the fence of "refresh" (knock down the selling price of the boat numbers)