New Cam for 502 Mag
11-18-2002, 09:30 AM
#1
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New Cam for 502 Mag
I've been chasing an ignition / fuel problem for half of the last season. I finally gave up and took the boat to a local merc tech. They chased all the symptoms, as well. I replaced the cap, rotor, pickup sensor, plugs, wires, coil and fuel/water separator (just in case of bad gas). The merc tech rebuilt the carb, checked the module and replaced the distributor gear.
Now I'm down to replacing the cam, timing chain and sprokets. The merc tech will just replace with the merc factory specs. Is there any other "fairly stock" cam I should look at? I want total reliability, reasonable price, and quick delivery. Not looking for big HP upgrade packages, just something that will make it run strong and reliable. The boat will probably go up for sale this spring, so performance gains are not necessary. Engine will idle smooth, just way out of time and will not advance like it should. The rest of the engine is bone stock Gen V with 410 hours, except for a electric fuel pump and K&N arrestor. The boat is a '92 Baja 240 Islander, Bravo 1 (1.36) approx 4,200 lbs. I've previously had this boat up to 68 gps at 5200 rpms w/ 21P Mirage. Some say I should be faster.
Open for suggestions. Thanks.
Now I'm down to replacing the cam, timing chain and sprokets. The merc tech will just replace with the merc factory specs. Is there any other "fairly stock" cam I should look at? I want total reliability, reasonable price, and quick delivery. Not looking for big HP upgrade packages, just something that will make it run strong and reliable. The boat will probably go up for sale this spring, so performance gains are not necessary. Engine will idle smooth, just way out of time and will not advance like it should. The rest of the engine is bone stock Gen V with 410 hours, except for a electric fuel pump and K&N arrestor. The boat is a '92 Baja 240 Islander, Bravo 1 (1.36) approx 4,200 lbs. I've previously had this boat up to 68 gps at 5200 rpms w/ 21P Mirage. Some say I should be faster.
Open for suggestions. Thanks.
11-18-2002, 10:40 AM
#2
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Posts: n/a
Camshaft
I really believe that a good camshaft for use as a stock replacement is the Edelbrock Torker Plus. I have used it on many rebuilds such as yours and it really works great. It is just a little more powerfull and works well with the 454/502 Magnums valve springs and non adjustable rocker arms. It is also very reasonably priced. The part number is 5062.
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE
11-18-2002, 04:29 PM
#3
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Thread Starter
Thanks for the input Dennis. I've located the cam and was wondering is the Torker Plus a direct replacement for Merc #431-9830? Initially, looks like a huge savings over the Merc stuff (Duh!!) and the timing chain set for about $50 is about half of the Merc parts.
Anybody else have some packages that you've used with success?
Anybody else have some packages that you've used with success?
11-18-2002, 08:15 PM
#5
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B4 you go to all the work replacing the cam, I'd be looking at ignition again. You say that the module checks out, but the timing doesn't advance. With the Mercruiser ignition, both of those cannot happen. It will either advance or it won't. It may however act up when it gets warm.
How was the module checked? What is your base timing and what is it at full advance?
Have you checked to make sure the balancer isn't spun. Something does not add up and its very rare that you can wear out a BBC timing set in a boat in 400 hours.
Rod
How was the module checked? What is your base timing and what is it at full advance?
Have you checked to make sure the balancer isn't spun. Something does not add up and its very rare that you can wear out a BBC timing set in a boat in 400 hours.
Rod
11-19-2002, 12:16 AM
#6
Charter Member # 55
Charter Member
KC, so the Merc tech said he didn't know WTF was wrong????
Why did he replace the dist gear??? If it was worn that badly, then chances are the cam gear is just as badly worn.
I had a similar problem in drag car before. We'd set the timing, put a load on the engine, and 5 mins later the timing was off again. It was bad gears on the dist & cam. Not sure which one actually failed first.
It isn't that hard to check the cam gear w/o pulling the cam. Just pull the distributor and look down the hole with a light.
If the tech thinks you've got something wrong in the valve train, he should have run a vacuum test and there are specs in his manuals to tell what the readings should be.
Why did he replace the dist gear??? If it was worn that badly, then chances are the cam gear is just as badly worn.
I had a similar problem in drag car before. We'd set the timing, put a load on the engine, and 5 mins later the timing was off again. It was bad gears on the dist & cam. Not sure which one actually failed first.
It isn't that hard to check the cam gear w/o pulling the cam. Just pull the distributor and look down the hole with a light.
If the tech thinks you've got something wrong in the valve train, he should have run a vacuum test and there are specs in his manuals to tell what the readings should be.
11-19-2002, 07:40 AM
#7
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Griff has a valid point about changing the dist. gear. If it was worn enough to replace, the cam gear might be damaged as well. If the dist. gear was changed because it was actually bad, you should also be looking at the bushing in the end of the dist. Its probably worn and should be replaced as well, otherwise you'll be right back where you started.
If you post actual timing checks and testing procedure, we may be able to offer some more insight.
Rod
If you post actual timing checks and testing procedure, we may be able to offer some more insight.
Rod
11-19-2002, 08:43 AM
#8
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Thread Starter
rpm... to check the module, he installed a new module and had the same result. Therefore, my module should be OK. I regards to the balancer, I'll ask. How is it that they "spin out". I assumed it was a solid piece.
Griff... I failed to mention that he replaced the distributor gear because there was about 3/4" of play in the rotor (rotated back and forth). He inspected the cam gears and stated that they were "like razor blades". I took that to mean that they were worn as well. He had hoped that replacing the distr. gear would suffice, but in reality it still did not cure the timing problem. My thoughts are that the cam gear is worn as well.
I'll also ask about the vaccuum tests and be sure that it was done also. I'm not sure of the actual timing checks and testing procedure. It really surprised me when he told me that the cam had to be replaced and that he was only going to charge me for the cam replacement and not all the exploratory work. (no less than 12 hours). This guy has a small shop and is very trustworthy. I want to keep him happy and I feel he want's to do the same for me. The best part is is that his shop rate is only $40 per hour!! I'll save about $300 if I buy the Edelborck parts online and give them to him to install.
Griff... I failed to mention that he replaced the distributor gear because there was about 3/4" of play in the rotor (rotated back and forth). He inspected the cam gears and stated that they were "like razor blades". I took that to mean that they were worn as well. He had hoped that replacing the distr. gear would suffice, but in reality it still did not cure the timing problem. My thoughts are that the cam gear is worn as well.
I'll also ask about the vaccuum tests and be sure that it was done also. I'm not sure of the actual timing checks and testing procedure. It really surprised me when he told me that the cam had to be replaced and that he was only going to charge me for the cam replacement and not all the exploratory work. (no less than 12 hours). This guy has a small shop and is very trustworthy. I want to keep him happy and I feel he want's to do the same for me. The best part is is that his shop rate is only $40 per hour!! I'll save about $300 if I buy the Edelborck parts online and give them to him to install.
11-19-2002, 02:29 PM
#9
Charter Member # 55
Charter Member
Cam gears should NOT be sharp "like razor blades" It sounds like the cam gear is worn. That would also contribute to the play in the rotor and give timing readings that jump around a few degrees. If its bad enough, it might jump a tooth hear and there too and really screw stuff up.
11-19-2002, 05:33 PM
#10
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Thread Starter
My thoughts exactly.
Vaccuum tests were completed per merc rec's.
They'll be removing the back seat and opening the front of the engine in a couple of days to determine what will need to be done. From what they tell me and from the knowledge of you guys, tells me I'm in the market for a new cam. That could be the only remaining thing... right?!?!?
IF that's the case, what would cause the cam gears to go within 400 hours? Is this typical? Should the distr. gear been replaced prior?
I can replace the cam and timing chain assembly from Edelbrock for the same money as replacing just the cam from Merc. Regardless, the cam from Edelbrock (they say) requires replacing the sprokets and chain with p/n 7810. The same parts from Merc run about $450 versus about $185 from Edelbrock. Is this legit? Is there any reason why I should go with merc parts in a stock motor?
Questions, questions questions....
Vaccuum tests were completed per merc rec's.
They'll be removing the back seat and opening the front of the engine in a couple of days to determine what will need to be done. From what they tell me and from the knowledge of you guys, tells me I'm in the market for a new cam. That could be the only remaining thing... right?!?!?
IF that's the case, what would cause the cam gears to go within 400 hours? Is this typical? Should the distr. gear been replaced prior?
I can replace the cam and timing chain assembly from Edelbrock for the same money as replacing just the cam from Merc. Regardless, the cam from Edelbrock (they say) requires replacing the sprokets and chain with p/n 7810. The same parts from Merc run about $450 versus about $185 from Edelbrock. Is this legit? Is there any reason why I should go with merc parts in a stock motor?
Questions, questions questions....
