GT40 compression, red flag??

[kylant]

I am looking at a 2001 Ski Nautique 196 being sold locally to me. it has 231 hours on it. The inspection report came back with 2 cylinders lower on compression. Cylinders 1-6 were 150-155, 7 was 120, and 8 was 130.

those lower numbers caught my eye right away. should i steer clear? have the compression rechecked?
seems odd that those 2 cylinders are low.
what could the causes be? what could i potentially be up against?
thanks

[malibud]

thats tough maybe a squirt of oil .. was it cold ? that teends to throw numbers off

[jpwhit]

Re-doing the compression test with oil added is a way to tell if low readings are caused by piston and ring issues vs valve issues. If the numbers go up when you add oil, then the issue is with piston / ring / cylinder walls. If the numbers stay the same after adding oil, then the low compression is due to valves or head gasket. But in either case, the compression isn't good. Adding oil doesn't mean the low reading is OK.

kylant low compression in a few cylinders isn't uncommon, and if it's only 10% or so off, then it's not typically considered a serious issue. But in this case, I think you can expect to have to do some non-trivial engine work on that boat in the near future. It'll run like it is, but with lower power. Hard to predict if it'll continue to degrade or stay constant. So, whether it's something you want to deal with or not, just depends on the price of the boat and your comfort level of dealing with potentially getting it fixed in the future.

Finding people to work on these older boats / engines is getting much harder. Less of an issue if you're someone that feels comfortable doing engine work yourself.

[Rednucleus]

Shows you these low hour decades old boats do not appreciate not being run on a regular basis

[Jonny Quest]

A cold engine compression test is good to do. Also, a warm engine compression test should then be performed. That should be followed by a leak-down test on a warm engine. That 3 test combo provides more complete data for you to consider.

JQ

[kylant]

what does a gt40 rebuild run?

[jpwhit]

Prices can vary quite a bit and just depend on the rebuilder. Problem may be finding someone that'll even do it. If you want a price quote, check around to see if you can find someone that'll do rebuilds on a GT40. They'll also need an engine machine shop that'll do the machining on a GT40.

[charlesml3]

what does a gt40 rebuild run?

You really aren't at that point. You have one cylinder that's a little low. It could likely run for years more like this. Do some more testing but this isn't a giant "red flag."

[Jonny Quest]

I concur -- you are not at the point of needing a full engine rebuild. If and when you do, the GT40 is nothing more than a Small Block Ford 351 Windsor (5.8). Any reasonable machine ship should be very familiar with that engine. If they aren't, find a different shop. These engines are in a zillion pickups from the late 80's to early 90's. The marine "special parts" have nothing to do with a standard rebuild.

JQ

[Naughty98]

Spot on, run it till it don't run no more. Then you can rebuild it.