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74 L low power bad dist bushing time 2

T

tnsailorguy

Member
"Ok this is strange. Last spr

"Ok this is strange. Last spring I was left dead in the water. The problem turned out to be the bushing on the distributor had worn to the point the the teeth had worn on one side of the gear and boat stopped getting fire. We took the shaft from an auto 454 and machined a new bushing. Sunday the on a cruise the boat began to lose power would not come up on plane. It ran fine around 2 grand. The mechanic called today and said the bushing was worn again. Luckily I had already purcheased a replacement and he is in process of replacing. Two senerios 1 the first replacement was not put together proberly and it eventually gave out the seccond would be some other problem possible a warped camshaft. It is unually for the bushing to fail in the firt place so i am concerned I may have a larger problem. Any thouughts? How much is a replacement camshaft for a merc 7.4? I know the engine will have to be pulled if that is in fact the problem. In the fall I had cut the engine off a 1800k and had gotten backwash in the cylender, cleared water and ran fine til the first bushing went bad. related?"
 
"Update. My Mechanic just repl

"Update. My Mechanic just replaced the distributor and adjusted the timing. The timing was off an inch. The boat started and ran just fine. He looked at the camshaft and it looked fine from the outside. His suggestion was to run it see what happens. If it goes bad again he felt like it would be about as cheap to put a jasper rebuild in. I am still hoping that the second distributor was flawed. Anyone heard of such? Is there any test to see if the cam is warped? Would it be about as cheap to do a rebuilt as to replace the cam, timing gear and chain? I mean it makes since that by the time you do all the labor for job like that you could be close in money and still have an engine with 500hrs."
 
"a mark IV flat tappet cam sho

"a mark IV flat tappet cam should be under $150, delivered anywhere. If the front of the motor is 'clear' - no bulkheads, putting a cam in should be much cheaper than a replacement engine. A roller cam should be ~ $300.

The timing being off an inch sounds like the new distributor went in a tooth off from the bad one."
 
"We took the shaft from an aut

"We took the shaft from an auto 454 and machined a new bushing.<<<<

I am not clear here??

You got a new dist shaft from a auto and put it in your housing after machining a new bushing and installing it into your housing

Is this the senerio?

If so it sounds like your housing was warped.
Did you align hone the housing? If not then you have no way of telling if the housing was warped.

I have seen this before. Typically there are a couple of senerios,
Housing is warped so bushings are not in alignment
Shaft is bent causing uneven wear on gear.
Gear installed 180 degrees out of original location and this causes a out of round condition due to wear.

These typically occur with inline motors and chrysler motors as the distibutors are on a angle when installed anyway.

Not very common on a chevy or ford V8"
 
"The engine would have to be p

"The engine would have to be pulled to replace the cam, thus there would also be a haul out bill. Kghost, It was an automotive shaft that was installed into the old housing. I had the thought of using the old housing as a template to fabricate a tool to test to see if cam is warped. It would be a plate that attaches to housing mount with a shaft dropping down onto the top of the cam with a small plate attached, thus I could mark the position of the veritcal shaft turn the engine and see if I do infact have travel. I am not familiar with the term "Align Hone"so not sure if they did that or not. I can ask."
 
"I highly doubt the cam is war

"I highly doubt the cam is warped.

Align hone would equal in your case, the two bushings in the dist housing were in alignment and to accomplish this you would "drill" "bore" then "hone" them to be to the correct size and in alignment.

Align hone is what is done to crankshaft mains when a block is reconditioned to make sure the main bearing caps are in a perfect straight line.

If you are unfamiliar with all of this you should not be rebiulding yourself and buying new or proffesionally rebiult parts."
 
"Kghost, What you said confirm

"Kghost, What you said confirms what I found from another mechanic. He said the the way the cam is mounted with a number of contact points along the shaft the it would be very hard for it to be warped without other issues being present. It seems to be a case of my cheap a** trying to save a buck or two."
 
"That is possible, but both???

"That is possible, but both???
Besides the cam is driving the dist shaft so it will only turn when needed.

A loose timing chain would show erratic timing mark when a timing light is used. the mark would occilate back and forth.

If you have seen this then maybe on one engine but I kinda doubt both. Maybe but unlikely.

Due to the cost of a new merc distributor I would seek out a local machine shop and see what they may be able to do. reallign with new bushings. Could get you a few more years.

You could have a warped dist housing????

Also the only reason I would suspect worn distributor bushing is either very high hours or lack of oil reaching them. The oil issue would be my first suspision. GM type vertical distributors last a very very long time!

I had a inline six GM nove and I went thru this, But the dist is on a angle, I replaced the bushings with oil light and aligned honed by hand.
Not perfect but effective. It last 1 year.....
I then bought a remanufactered one."
 
I had this problem awhile back

I had this problem awhile back on a Merc 5.7 litre. The bottom bushing on the Thunderbolt 4 distributor would wear on one side bad in only 20 hrs. Replaced with a new bushing and same thing happened plus it ruined the shaft this time. Bought a new dist. and it never happened again. The only difference between the two is the old original had two o-rings on the housing where it goes in the block and the new did not. I think the o-rings were worn allowing it to move sideways in the bore. The new dist. did not have two o-rings and fit tight in the block. Maybe this helps.
 
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