Compression test results / cost to rebuild

[Noquebay]

I am looking at buying a 1999 Sportster LX, it has the 310HP Indmar engine. I had the dealership do a compression test on all cylinders.

Would you be concerned about one cylinder testing @100 psi when all others range from 150 - 170?  the engine has about 1,000 hours on it. 

Any idea on what it might cost to rebuild one cylinder assuming it needs new rings and/or a valve job?

Comments from dealership are here:

Cylinder:
1) 165 psi
2) 170 psi
3) 100 psi
4) 160 psi
5) 150 psi
6) 160 psi
7) 150 psi
8) 170 psi

Cylinder 3 (2nd one back on the port side) showed low compression but the motor ran strong and didn't seem to be effected by it.

[Woodski]

@Noquebay:  to get a more accurate and ability to pinpoint the issue, run a leak down test.  That test will tell you whether rings or valves are the compression culprit.  The other cylinders look reasonable for 1k hours.

[Steve B.]

Interesting. I'm thinking a valve issue. The engine may run for a ton of hours like that.

Steve B.

[MadMan]

I'd use this data to leverage a heck of a deal....

[Andrew999]

I just ran one on my rebuild and they were all around 180psi it was a 350 block with 450ish hours on it. It's more about all of the pressure being within 5% or so. You've got a cylinder not doing something right. Rings, valves, over tightened spark plug and cracked it, who knows until you go digging. Did they Triple check that number? Sometimes the parts changers "mechanics" don't screw that all the way in or get lazy cranking it over. 

We thought one of mine was bad only showing 150 then went back and it was normal. 

If you get it for the right price run it and don't worry until you have to. Just a little less bang for your buck. Is my 2 cents but yeah leverage it. 

[Noquebay]

Here's the scoop, the boat is 4.5 hours away from me so I've not seen it yet but it looks to be in good shape the leaky cylinder aside.  It's a consignment sale at a dealership. The dealer says it runs strong and doesn't seem to be affecting performance.

I'm scheduled to go see the boat Monday morning.  If I drive that far to see it I will want to buy it....I'm thinking I'll try to get$500 or so off the price based on the cylinder issue.  I figure even if I spent $2k on rebuilding the engine I only have $10k into a solid boat.  In the mean time I could probably use it for a couple years before rebuilding it....

its a 99 sportster LX without any bells & whistles (no tower/speakers, etc) but it's priced at $7,900. 

I was hoping somebody would have insight into how much it might cost to hone one cylinder, replace piston and rings, and do a valve job...this seems like worst case. I don't expect ill need to rebuild the whole engine.

[Sixball]

As said a leak down test can tell you almost everything you will want to know. I would not let someone tell me its ok still strong runner. A bent valve could let go the next time it starts. A valve hanging up could be seizing could get piston to valve conflict! Bad rings? scored cylinder wall? Head gasket going?  Still could be a good buy but If I was not ready to work on it I might be slower to jump in. Could be a very simple fix or could be a block. I would want to know more!

[MadMan]

3 hours ago, Noquebay said:

I'm thinking I'll try to get$500 or so off the price based on the cylinder issue.

I would want a lot more than $500 of for a wounded motor.

[Choiceind]

13 hours ago, Noquebay said:

I am looking at buying a 1999 Sportster LX, it has the 310HP Indmar engine. I had the dealership do a compression test on all cylinders.

Would you be concerned about one cylinder testing @100 psi when all others range from 150 - 170?  the engine has about 1,000 hours on it. 

Any idea on what it might cost to rebuild one cylinder assuming it needs new rings and/or a valve job?

Comments from dealership are here:

Cylinder:
1) 165 psi
2) 170 psi
3) 100 psi
4) 160 psi
5) 150 psi
6) 160 psi
7) 150 psi
8) 170 psi

Cylinder 3 (2nd one back on the port side) showed low compression but the motor ran strong and didn't seem to be effected by it.

When I bought mine, I had inspection, the tech did a compression test and the very first cylinder was a little low, he came back to it at the end and retested it. since it was the first one he was thinking maybe not enough oil on the rings to make a good seal. He was right, all were 200 but 4&8 those were 210. The compression test was done before done before the fake a lake and a real engine run test. Just wasnt sure what order you did your test, cause if you ran it before the oil should be everywhere then. 

Edited September 18, 2016 by Choiceind
misspell

[MadMan]

Compression tests are done dry first, then if there is a problem cylinder, oil is added and the test rerun.  This is done to identify if it is a rings problem or something else.  If the oil heals it, it means the rings aren't sealing.  The oil that was added just acts as a very temporary sealant.

[Woodski]

@Noquebay:  The reason for my comment on leak down test is that will provide a lot of information on rebuild cost.  If a cylinder head or head gasket issue, you can simply remove the offending cylinder head and do the work on the bench w/o removing the engine.  If you need to attack the bottom end, engine needs to come out which will add significant cost & work to the fix.

[Sixball]

4 hours ago, Woodski said:

@Noquebay:  The reason for my comment on leak down test is that will provide a lot of information on rebuild cost.  If a cylinder head or head gasket issue, you can simply remove the offending cylinder head and do the work on the bench w/o removing the engine.  If you need to attack the bottom end, engine needs to come out which will add significant cost & work to the fix.

+1  Just so much more info from a leakdown. From someone who understands how to look for issues with the test. As said it makes the cost of work much easier to get close!

[Noquebay]

I went to the dealership today (5 hour drive) and checked out the boat.  I tooled around the lake on it for 30 minutes and it ran great, with it warmed up I did compression checks on each cylinder, after being warned up all 4 cylinders on the port side were 150+\- 5 psi (this includes the one that tested low when the dealership tested it cold).

i was prepared to spray some oil into the cylinder and rerun the test to isolate the issue to the head or the block/piston/rings but I didn't see any need to once the test went as well as it did.

so, long story short I bought the boat for a great price ($7,200)

There are some issues that need addressing though: water pump needs replacing, speedos are jacked up - one read 45 while the other read 10 when we were going about 30. Battery voltage gage is also on the fritz.  Other than these items the boat is in great shape..can't wait for the weekend!

i still plan on doing leak down tests on each cylinder since all 4 cylinders on port side are lower than starboard side..and there is a little more variation on the starboard side but all above 160 when warm.

thanks for the feedback on my post.

oh, and by the way this is my first Malibu boat!

 

Edited September 20, 2016 by Noquebay
Mispelling

[Woodski]

@Noquebay:  congrats and welcome to DD ownership and the Bu Crew.  Now that you have a Sportster, you will need to acquire barefooting skills for you and the entire gang that will participate behind your new vessel.  Enjoy.