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Max load on stock valves

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Old 11-05-2013, 06:26 PM
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Default Max load on stock valves

I was wondering what the max valve spring pressure the stock 7.4 mag valves can handle? I am moving up to a roller set-up on both motors and they happen to be triple springs, I dont want the spring pressure to be to high, I have had my fair share of losing the top of a valve.
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Old 11-06-2013, 02:42 AM
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Triple valve springs?.... how big of a cam you running? Any reason you would be against swapping the valves out for better ones?
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Old 11-06-2013, 07:19 AM
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Tell us more about this triple spring you'll be using? A hydraulic roller in a marine 454, should not need anything excessive as far as spring pressures go.
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Old 11-06-2013, 07:35 AM
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Originally Posted by trent77969 View Post
I was wondering what the max valve spring pressure the stock 7.4 mag valves can handle? I am moving up to a roller set-up on both motors and they happen to be triple springs, I dont want the spring pressure to be to high, I have had my fair share of losing the top of a valve.
Do you know the spring pressure ...on the seat and at full lift ....Do you know the cam specs...Are you buying used setups/
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Old 11-06-2013, 08:11 AM
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Hopefully; he is referring to a dual spring with dampener.

To answer your question;
I would be concerned about type of valves, stock or stainless intake or inconel exhaust.
Measure for stem wear and taper, how much margin is left on valve face.
Run-out, is it bent or warped.
Corrosion, pits of any.
Inspect; lock groove. Signs of loading and unloading valve locks, retainer. ( Valve float or detonation, will pound the valves and retainers)
Inspect; tip of valve for wear and rolled material at edge of stem and top of valve( This would be obvious; you would have a hard time pulling valve out of the guide.)

I would also at this time; check all of the valve guides for wear with a bore gauge.
If high time; has been put on heads and heads have had valve jobs in the past. You need to determine; if you are sinking the valves, have any valve seats been receding which you will need to have new seats installed. Sometimes, by the time you replace all of these items it's cost effective to by new cast or aluminum heads complete with stainless and inconel valves.
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Old 11-06-2013, 08:57 AM
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It is a new set-up comp cams extreme marine kit k11-451-8. I am sorry I dont have money on trees, and was just asking if anyone could give me a little help. The engines are low hour engines, but sat for three years and I am rebuilding the old junker and want everything to be as trouble free as possible. I am not going extreme by any means, and the spring assembly has three springs, which one may be the dampner, im not familiar with those. I have this kit on my 496 and I love it, but I have AFR heads and i bought the inconel exhaust and and AFR extreme intake valves for them. I am just asking from the stock side of things, because I am really unfamiliar with stock engines.. FYI .547 is amount of lift
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Old 11-06-2013, 09:04 AM
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Trent, I don't know if you are going to get an exact answer to your question. I ran a set of stock intake valves with around 160 lbs seat and 400 lbs open with no apparent issues, but the exhausts were switched out to extreme duty inconel valves.

From the nature of your question, it sounds like you are going to a high lift roller cam and you are trying to save some money by re-using some of the stock parts here and there. First of all, if you are re-using the stock valves, have you made sure that you are not going to encounter a coil bind situation at full cam lift with the stock length valves? Sometimes running very high lift cams will require a longer valve to allow more room for compression of the spring. What about locks and keepers? These should be properly matched to each other and to the spring you will be running. If it truly is a triple spring, it requires a special retainer that has the steps in the correct place for all of the coils. After you figure that out, you will probably have to calculate the correct pushrod length to ensure correct valvetrain geometry, especially if you have to go with the afore-mentioned longer valve stems.

I have no idea how experienced you are on building engines, and I am far from an expert, so I don't want to make it sound like anyone is talking down to you. However, a lot of folks run into trouble when they start swapping cams in these engines without knowing all of the relationships of the various parts in the valvetrain and how these will be affected by the cam swap. It can be a lot more complicated than going to a catalog and ordering a stout cam and a set of hefty roller springs and swapping them into your motor. Hopefully you are getting some guidance from a reputable shop who has experience with a lot of marine engines to steer you in the right direction - assuming you are a relative "newby" like me. I had to learn the hard way on my engine, and I would love to save others the pain of having to do it more than once due to incompatible parts, poor machine work, cutting corners, etc.

If you have all of this part figured out and I am overstepping my bounds, I apologize in advance. If not, feel free to ask questions. Sorry if I could not provide a direct answer to your initial question. Good luck!
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Old 11-06-2013, 09:08 AM
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Valves aren't gonna snap from those springs, if that's what your asking. What MER is implying, is the important factors are the condition of things in the heads. Hours don't mean much in my eyes .You can have a engine with 5 hours that has tuliped valves, guide wear, all sorts of issues. The material of the valve is also important like he said.

So, to start, what cylinder heads do you have? GM Rectangle port or Oval port?
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Old 11-06-2013, 09:09 AM
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Quote:
Originally Posted by trent77969 View Post
It is a new set-up comp cams extreme marine kit k11-451-8. I am sorry I dont have money on trees, and was just asking if anyone could give me a little help. The engines are low hour engines, but sat for three years and I am rebuilding the old junker and want everything to be as trouble free as possible. I am not going extreme by any means, and the spring assembly has three springs, which one may be the dampner, im not familiar with those. I have this kit on my 496 and I love it, but I have AFR heads and i bought the inconel exhaust and and AFR extreme intake valves for them. I am just asking from the stock side of things, because I am really unfamiliar with stock engines.. FYI .547 is amount of lift
Sorry, I had already hit send on my other post before you posted your detail. .547 lift is pretty mild, and should not require an extremely aggressive spring. Were the springs matched to the cam? If so, they should not require extreme seat pressure. Judging by that, stock valves should work OK - I ran a 454 that had stock style valves with a similar lift flat tappet hyd cam for years without problems. You mentioned that you had problems snapping the stems off of valves. That should not be happening, and you need to carefully explore the true cause of the problem if this is the same engine you are building.
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Old 11-06-2013, 09:17 AM
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I have rectangular port heads. The weird thing is the boat is a 1993 and one of the motors is a gen V and the other is a gen IV. The previous owner is original owner and said never swapped motors, so I guess it came like that. I have not talked to my shop yet, being I wanted a little input before ordering these.The problem here in deep south Texas our engine builders are good roundy round dirt track builders. Most of our boats around here are diesel offshore rigs. I just wonder what the stock valve pressure and max lift of the merc 7.4 mags are? Are the exhaust valves already inconel?
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