compression test results 454
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=34187
Printed Date: October-08-2024 at 8:37am
Topic: compression test results 454
Posted By: cbr1000dude
Subject: compression test results 454
Date Posted: July-18-2014 at 11:06pm
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So I bought this 1988 Barefoot Nautique with a 454 engine taken partially apart. Everything looked OK, some surface rust. It turned over, so I got a gasket set, cleaned everything, and put on the heads, push rods and rocker arms, adjusted lash. Compression is 150-160 except for #5 has only 65 pounds,#7 has 120. Tried adding oil through spark plug hole, didn't increase. So what, bad valve seat? If it was a stuck or broken ring wouldn't it increase with oil added? This engine has 560 hrs, but hasn't run since 2001. I'm trying to do this on a limited budget. Any advise on a logical next step would be appreciated. |
Replies:
Posted By: TRBenj
Date Posted: July-19-2014 at 12:32am
| Leak down test. |
Posted By: cbr1000dude
Date Posted: July-23-2014 at 5:05pm
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OK, I was finally able to do a leak down test. The #5 cylinder had 40 percent leakage coming from the cam area, no noise at intake or exhaust. All the rest tested between 25 and 40 percent, even the ones with 160 compression. I kept checking for TDC with a straw, and loose rocker arms, but the results didn't change. The dial says this is "moderate", but from my reading this is too much. Of course I'm testing a cold engine that hasn't run in 13 years. So back to my original question, is it worth putting together and see how it runs, or a waste of time and energy. Opinions please! |
Posted By: MrMcD
Date Posted: July-24-2014 at 4:11am
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The weak cylinders may be slightly rusted and not sealing well. You mentioned installing new gaskets? Head gaskets? The rings may be stuck in the ring lands of the pistons from sitting so long. Sitting an engine will have some valves open and some closed. Closed valves usually sit well with no damage. Open valves will take moisture from the air while sitting and eventually there will be some rust on the valve, head and cylinder wall. Squirt a good amount of ATF fluid in the low cylinders, it is high in lubricants and cleans well. Some mix the ATF with Acetone 50/50 and claim that works even better. It may free up a stuck valve or piston ring and get you ready to go. If rusted severely a cylinder will not rebound and seal up. If the rust is moderate it may seal up just fine. If not you are looking at a valve job or maybe a bore and hone on the block. Maybe you have a bore scope that you can shine into the cylinders and look prior to pulling off the heads. Harbor freight has a cheap bore scope for $150 or less. |
Posted By: cbr1000dude
Date Posted: July-24-2014 at 7:03pm
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Sorry if I assumed you read the other thread. I bought the boat with the top of the engine apart, so the heads were off and valves closed sitting on a work bench. The bores had just a slight surface rust in several places, but cleaned up fine. Heads too. I took the readings after installing the heads with new felpro gaskets, got the set. I'm cleaning the intake manifold gasket surfaces and carb today. I'm just going to forge ahead and see how it goes. Thanks for your comments. |
Posted By: DayTony
Date Posted: July-24-2014 at 8:06pm
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So those numbers seem kind of high for a leak down test but considering it hasn't been run in so long chances are you have multiple rings which are either not seating or stuck. also you said the bores were rusty? thats your first clue of possibly needing to pull the motor. rust doesn't just accumulate, it takes the place of apparent material. in removing the rust you may have opened up your piston to wall clearances. And if you had one cylinder that was at the top of the tolerance to begin with and had to resurface and hone it you could have easily taken it out of tolerance. But with results like that and the history of the engine it sounds like rings are going to give you an issue if you just assemble it. not sure your capabilities but if it were mine, i would do the quick rebuild check if i were looking to get use out of it this season. Pull it, hone the walls clean and check the piston to wall clearances, if ok, new rings, oil pump, seals, gaskets. check all the bearings, check the thrust while you have the crank out. Then re-assemble. It sounds like you already have the top end freshened up why not go through the lower end? there has to be a reason the heads were off when you bought it. -Tony |
Posted By: DayTony
Date Posted: July-24-2014 at 8:17pm
| i want to clarify too that "getting use out of it" this season and struggling to keep her running and dealing with blowby issues but still floating and moving are two different things haha. |
Posted By: cbr1000dude
Date Posted: July-24-2014 at 11:25pm
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The rust on in the bores came off with just rubbing an oily cloth on them, so no metal loss to speak of there. I think the stuck rings theory is most likely. Oh, the PO had the heads pulled because he thought the engine was frozen, but it was just a bad ignition switch connection as far as I can tell. He also removed the intake manifold with the carb still on, and the hard gas line still attached! Weird. I have a 90 SN in great shape to use this summer, so this is just a project/hobby to work on. Pulling the engine parked in my sloped driveway could be a real pain. I have a garage and shop on the family ranch I could use if it came to that. It's just nice to have it here so I can play with it in the cool mornings for a couple of hours while everyone is still asleep. Boys and their toys. 
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Posted By: MrMcD
Date Posted: July-24-2014 at 11:47pm
| That being the case, little to lose, lots to gain, fire it up and run it a while. You may find it seats up after an hour of run time, or it will smoke like a locomotive and need a rebuild. Anything in between is possible also. Good luck with this engine. Sounds like you may be able to wake it up again. |
Posted By: DayTony
Date Posted: July-25-2014 at 12:01am
| I have to agree as much as it goes against all logic lol. You've already got the heads on. Bolt up the intake and give it a go. On the small chance the rings free up (im never that lucky) |