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Crusader model 350454 slight tapping noise

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powerboater41

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I have a 1978 crusader engine

I have a 1978 crusader engine that is making a slight tapping noise around the #6 #8 cylinder. I had a compression test done and all cy came in at 120-130 but the # 8 was at 60 psi. The engine runs fine. The floor will need to be taken out to do a leakdown test. The mechanic from my marina told me that he feels that its 99% the rings. Would worn rings make a slight tapping or pssft noise? I asked on this issue before and was advised by members to leave it alone if it is rings. I changed the plugs and the # 6 and # 8 had a lot were oil fouling however the plugs were old about 3 yrs old.
 
"Both the oil fouling and the

"Both the oil fouling and the compression tend to point to the rings. However, I'm not convinced that explains the tapping noise. More likely that is the top end, up to and including a worn cam lobe. How many hours on the motor?"
 
doug:

you have no idea how

doug:

you have no idea how many ring jobs have been sold based on a feeling - a leak-down test will be definitive proof.

Dave's suggests have much merit. you can usually pull the rocker cover and examine the valve train on that side. A dial indicator will also let you check the cam at the same time (1/2 anyway).

How are the hoses from the rocker covers to the flame arrestors?
 
Thanks for the replies. The mo

Thanks for the replies. The motor has about 1400 hours on it. will a leakdown test involve removing the valve cover? The engine sits very high in the boat. If one was to remove the exhuast manafolds there would be room to look at the valves. I can pull up the carpet and pull up the floor to get better access. Can a bad ring or cam lobe be fixed in the boat? What would this cost. Labor in my area is 75-85 hr. thanks in advance for your help
 
"What about adding a little oi

"What about adding a little oil to the cylinders and repeating the compression test.
If it improves, it's the rings, if it doesn't, it could still be either one, but most likely the valves."
 
"Doug, How do you change the

"Doug, How do you change the plugs on this boat? Is'nt there a way to get to teh sparkplugs? The leakdown test really could just use the sparkplug hole. If you are not at the top of the compression stroke and there is a problem with the valves seating properly, removing the valve cover will be helpful. You may hear the escaping air so take your time and maybe even bring a mechanics stethescope (age dependant)

1400 hours is getting up there but my belief is that it all depends on the care and maintenance of the previous users

On some very old vintage 1930's era motorcycles, leaks of 25% were still useable. I am sure you will like to see less than that however."
 
"I had a mechanic take a look

"I had a mechanic take a look at the engine and he used a camera that went into the spark plug hole and used to inspect the cylinders. he found that the #6 was using some oil (might be scraper ring) but that the cynlinder walls looked great, they still had the cross hatch pattern on them. same with # 8. he felt that the low compression and tapping was due to a cam lobe. He also took off the valve cover and could not see any of the valves moving up or down more or less than the others when he turned the engine by hand. Could this be a burned valve? I would think that a worn cam would cause compression to go up not down. since the valve would be shut not open. What ways can one tell if a valve is to blame? Any help would be great."
 
"A worn intake lobe will reduc

"A worn intake lobe will reduce air intake, and reduce the compression value.
Since the valve cover is off, i'd check the valve lash. See the recent thread on lash adjustments. It won't take much wear to cause tapping and maybe even the low compr. reading."
 
"The 454 uses rocker arm nuts

"The 454 uses rocker arm nuts to correctly set the preload on the lifters. So, for a high hour engine, cam, push rod, rocker wear, or even a loose adj. nut can cause tapping. I should add that just because the tapping can go away with an adjustment, doesn't mean all is well. Many if not most of those wear items, once the outer hardened layer is worn off, can wear at an accelerated rate. An adjustment may be worth a try. A more rigorous method is to actually measure valve lift with an indicator. An eyeball measurement is not good enough.
Another option is to idle the engine with a valve cover off. You can then grab stuff and perhaps find the loose parts that way."
 
"Hydraulic lifters often make

"Hydraulic lifters often make that type of sound if they get a speck of dirt in them, and sitting around for months (as boat engines often do) can cause them to collapse. It takes time and oil pressure to 'pump' them up again, along with eliminating any trapped air.

Then again, as DD suggested, you might have an adjustment that's off. If so, the valve covers have to come off.

Jeff"
 
"I had a simlar problem with s

"I had a simlar problem with some top end tapping and a slight backfire at high RPM. 1400 hours on 1984 Crusader 454's. A "mechanic" adjusted the lifters by turning down the rocker nut and just exactly as Diver Dave explains, the hardened surfae of the cam was quickly worn away along with 1/2 of the lifter.

I suspect you may have a worn cam lifter but if you are luckly only an adjustment to the rocker nut will be indicated.

And yes you can replace the cam in the boat so long as you have clearence to slide the cam shaft out in front of the engine. I had the clearence and it was no big deal to replace the cam, lifters, push rods, and rocker nuts. The nuts can and do lose their locking power and on an engine as old as yours new ones are the way to go."
 
I had felt it necessary to cha

I had felt it necessary to change the nuts when I did mine 2 years ago.. The nuts were about $2.00 each from Chevy...That rocker ball was over $5.00...I re-used those but the dealers have some leeway with pricing...it pays to ask.
 
I am having a mechanic do a le

I am having a mechanic do a leak down test here in a few weeks. I found out that the oil I used for the last oil change did not have enough zinc in it so I added STP oil treatment(blue can) to the engine. After about 30 secs of running the engine quieted down alot. I could hear it outside the engine room and then I could not. You can still hear it in the engine room. dont know if that rules in or out cam or lifters?
 
"If you are using post SJ rate

"If you are using post SJ rated oil, you might consider adding ZDDplus or similar zinc product."
 
"Thanks Dave,

I did some se

"Thanks Dave,

I did some searching and found that if you add STP it will bring SM rated oils up to around 1500 on the zinc. I plan to use delco 400 next time so I dont have to add any ZDDP"
 
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