Push rod issue

[bellboy120]

I have a 1978 bellboy. It has a 120hp omc motor I/0. I replaced head with a rebuilt one. If you’re in the boat and looking at the motor, the push rod on the fourth value back on the second cylinder moves twice and fast as the rest. Also, their is no compression if you tighten valve. I replaced the hydraulic lifters. I feel like I have isolated the problem to the push rod and not the valve spring not working right. With the rocker arm off the push rod I held the push rod and it had the fast movement while turning the motor over. Is this a camshaft issue or something else?

 

[Don S]

Re: Push rod issue

Each valve should open one time every two revolutions of the crankshaft. Are you saying it's opening and closing more than once in 2 crank revolutions? If so, the only way that could happen is to have 2 lobes on the cam (which I doubt you have) or are you saying the valve opens and closes faster than the other valves? If that is the case, then the lobe is probably worn off the cam. Don't see how it could be a push rod problem, all it is is a tube of steel, no moving parts.

 

[bellboy120]

Re: Push rod issue

Thanks Don,<br />Latter, statement you made is correct. Any words of wisdom on pulling out the camshaft. Don you helped me in the past and am very grateful. If you have a moment could you view a question I have about my steering situation at Boat Topics and Questions (not engine topics). Thank-you.

 

[Don S]

Re: Push rod issue

The first thing on your engine, is do you have a manual? If not, get one. <br />You will need to pull the side covers, and remove the lifters. ALWAYS put new lifters on a new cam. Never use the old ones.<br />Regarding your steering, from my experience DJ & Shep already answered your question.

 

[paulie0735]

Re: Push rod issue

Sounds a little odd to say the least, was the engine running ok before the work or is this the first time you have attempted to run it? Check that the push rod is the same length as the others and that the rocker arm is also the correct one.

 

[bellboy120]

Re: Push rod issue

Paulie,<br />After purchasing the boat, I could not get it to run. I took the motor apart shorlty after. One of the valves was burnt. The head appeared to be in bad shape, so I replaced it. I had all the push rods together at one time and they seemed to be the same length. The rocker arm looks the same as the rest. Do you think the problem might not be the cam? As for Don's comments, I do have a manual. The manual talks about specical tool to remove the camshaft gear. Do you know a site online to purchase this tool.

 

[Trent]

Re: Push rod issue

First you need to check the cam lift before even thinking about removing the cam. AS was said you need a manual for this engine. Dont pull the engine apart before checking the lift. You will only need to remove the valve cover to do this.

 

[DHPMARINE]

Re: Push rod issue

If you are looking at the pushrods while cranking the engine and one is moving faster than the rest, I'd think you still have a compression problem.<br /><br />DHP

 

[paulie0735]

Re: Push rod issue

bellboy,<br />If you have not had the engine running than it sounds very suspect. You may not want to hear this, but my best advice for you now is to 'invest' a hundred bucks or so and get a merc mechanic out to have a look and diagnose the problem correctly (and check the rest of the installation while he's there). Might be the best money you ever spend on your new boat. From there you can determine what work you can do yourself and what needs a pro's touch. Good luck.

 

[Reel Poor]

Re: Push rod issue

Like DHP said the only way that push rod can move faster is if the enging cranking speed increases, i.e. due to lack of compression, and not on that clyinder. My guess if this is whats happening compression loss is probably on #4 cylinder.<br /><br />Go ahead and install the pushrods then do a compression test. Also check cam lift, note that intake and exhaust lift may be slightly different.<br /><br />All that being said this would be a truly unique problem.

 

[paulie0735]

Re: Push rod issue

If your still keen to ‘do it yourself’ than try this, drop the push rods in and leave the rockers off, remove the spark plugs (this will make it easy on your battery) and turn the engine on the starter;<br />Do all the rods move up to the same height and at the same speed? (this different speed that you speak of is the bit that I find odd in your original post) if they do than move on, if not than stop as you have a cam or lifter problem. If they seem ok than next connect all the rockers and adjust (are you confident that you are adjusting them correctly?). Again turn the engine on the battery and observe the rockers. Do all the rockers go up and down the same amount? If not than stop, you have a rocker problem or you are adjusting them incorrectly. If all looks fine than replace the spark plug in number one and do the compression check, (only fit the spark plug in the cylinder that you’re checking again making it easy on your battery), also set the throttle at wide open while you’re doing the compression test. Work your way through the other 3, write down the numbers and let us know what you find. If all this is not clear and fully within your understanding than its time to call in the mechanic. There is nothing wrong with calling in some help, even the pros do it! <br /><br />I think you have a few of us intrigued!

 

[paulie0735]

Re: Push rod issue

opps, can't do the compression test with the spark plug in.......... hummmm must be lunch time, got my mind on a nice juicy hamburger!!

 

[rodbolt]

Re: Push rod issue

easiest way to check cam lift is to remome the plugs, use a si inch scale. place the proper socket on the alternator fan nut to rotate the engine in the proper direction. now while rotating the engine measure the pushrod lift from the gsket rail to the rocker at the pushrod, all intkes should be the ame and all exhaust should be the same. the cam is induction hardened so if it wears a little suddenly it hits soft steel(iron) and wipes the lobe off.<br /> if # 4 has a lower lift next step is to remove the lifter and check for a stuck plunger. I like to measure the actual lift of the lifter body to eliminate the plunger as a source of lck of motion. if the cam lobe is worn any machine shop can replace the cm gear.

 

[Buttanic]

Re: Push rod issue

This definately sounds like a cam problem. No way loss of compression in one cylonder can cause the push rods in that cylinder to move faster than the others, no way.

 

[bellboy120]

Re: Push rod issue

Hi all,<br />I just want to thank all you for taking the time to give me advice and shed light on the problem. Unfortuntly, I don't have the time this week to work on it so, I'll look at it this weekend. In the meantime, I'll read the manual so I can ask more technical questions as they arise. Thanks for the adivce. Being a backyard mechnican I always get worried when I see in the manual that you need a special tool. Where does one get these tools from?

 

[Buttanic]

Re: Push rod issue

The cam will come out of the block without having to remove the gear. There are two holes in the gear that will need to be aligned with the two bolts that hold the cam retainer plate to the block. Once the bolts are removed the cam and gear will slide out. A press is all that is needed to remove the gear from the cam once it is out of the block. I am not sure what the "special" tool is but I suspect it is some type of puller to pull the gear off the cam with the cam still in the block.