Need advice engine compression on challenger 1800

[Leopoldo Moreira]

First I want to congratulate for the comunity, a lot of informations here!

I am about to purchase a 99 challenger 1800 twin it look to be a low hour boat and in good shape, Seller told me that both of motors have been rebuild (top end) recently only used about 4 times. But in the compression test I got some worries, in the test it show 120 PSI in all 4 cilinders, but mechanical told me that it is a good compression and it goes from 100 to 140 psi in new conditions, from my research in the forum it does not seem to be true can be up than 170 psi in new condition. I am right?


Motors with 120 psi are in good shape? still strong?
I should consider a soon rebuild on them?
Why it is showing low compression after rebuild

thanks

 

[Coastiejoe]

150 is perfect, 135 is very good, 120 is still good but an indicator that you will be doing work in the off season. 110 is low.

Most can get away with just a top-end. But,,, depending on how many total hours are on the crank, it sometimes isn't worth doing just the top.. 200 hours seems to be where 2-strokes need to get re-worked (top-end). Salt water contributes to how soon and what work needs to be done.

 

[Leopoldo Moreira]

It is not from salt water

 

[Dr Honda]

First of all... don't let that HACK work on your stuff anymore. The 720 or 800 Rotax engines spec out at 150 psi. At 120... it's on it's way out, and will shortly eat itself. (assuming it was built properly in the beginning) Basically... when you loose top-end pressure... the rings are going bad. When the engine is running... those leaky rings can no longer seal the VERY HOT combustion gasses in the top-end. The blow-by that gets past the rings, will over heat the piston skirts... and eventually you melt the piston.


With that said... if some low HP engine that specs 100 psi... then that engine is fine.


WITH A COMPRESSION TEST... THERE IS NO SUCH THING AS A RANGE THAT BIG !!!! IT'S A VERY SPECIFIC PRESSURE RANGE YOU ARE LOOKING FOR !! (period)

 

[Isaac-1]

One more thing to remember, not all compression gauges are equal, a cheap import compression gauge may read lower than it should.

 

[Sportster-2001-951C-Stock]

North of 140 is a healthy engine, 120 is too low needs rebuild. Check your gauge and be sure it's correct.

30 minutes water testing the boat is strongly recommended if being sold as turn-key running condition.

If not the above, the budget must include engine(s), and possibly pump(s) overhaul $$$