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It's good to be alive
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Discussion Starter · #1 ·
My friend has a N/A BBC 509 Merlin II block 650 hp (so no wild cam or springs) motor that he just snapped his second timing chain in 3 years. Any ideas on what would cause this? He is thinking of using a gear drive this time around.

thanks in advance
 

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AKA Blownjet 468
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1,193 Posts
what kind of chain was breaking? quality true roller USA made? or other.
if you do go to a gear drive, don't even think about using one of those
"dual idler" junk pieces! make sure it's a 3 gear, with the idler in the cover.
I have replaced more of those junk ones in peoples motors than I care to
remember, and every one was either ready to split the dogbone, cracked
there, or so sloppy it would have gone soon! the pins for the idlers also
like to machine nice circles in the block when the gear galls to the pin!
 

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It's good to be alive
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1,498 Posts
Discussion Starter · #5 ·
what kind of chain was breaking? quality true roller USA made? or other.
if you do go to a gear drive, don't even think about using one of those
"dual idler" junk pieces! make sure it's a 3 gear, with the idler in the cover.
I have replaced more of those junk ones in peoples motors than I care to
remember, and every one was either ready to split the dogbone, cracked
there, or so sloppy it would have gone soon! the pins for the idlers also
like to machine nice circles in the block when the gear galls to the pin!
yes double roller good chain
 

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E-7 Sheepdog (ret)
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6,625 Posts
Somethings not right if he is going through timing chains that fast. I would figure out whats going on before I did anything else.
Yes, something is VERY not right if it is eating chains like that and does not have "wild cam or springs".

Just slapping a roller setup in it is not going to solve an alignment issue if one exists, and that is about the only thing I can imagine happening there. Only about 6 parts involved, grand total (from crank thru the cam) and not a lot of things can be "wrong" other than alignment and spacing.
 

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Registered
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Many suggestions above starting with allignment. Something that hasn't been mentioned is there is a possibility that it is not recieving enough oil. have him check that one of the front gallery plugs is drilled to spray oil on the chain. I don't remember which plug it is off hand but there are two or three next to the cam. Another thought it was set of for a torington bearing, gear spacer and that has been taken out. As usual, when it's figured out, report.
 

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It's good to be alive
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Discussion Starter · #10 ·
Many suggestions above starting with allignment. Something that hasn't been mentioned is there is a possibility that it is not recieving enough oil. have him check that one of the front gallery plugs is drilled to spray oil on the chain. I don't remember which plug it is off hand but there are two or three next to the cam. Another thought it was set of for a torington bearing, gear spacer and that has been taken out. As usual, when it's figured out, report.

thanks for that, anyone want to comment?
 

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Some guy
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thanks for that, anyone want to comment?
That's a typical modification, you can do both instead of just one if you like. A .040" hole is what I am used to using.

I don't know that there is a valid reason for a chain failing without the extra oil though, tons of engines run without an "oiler". I would be exploring everything else mentioned. One other thought, who replaced the chain after the first one broke? Was only the chain replaced, or the entire timing set? If the chain only, was it the same brand,, not just one that kind of fit?
 

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hi guys i am the one that franky posted this for i pulled the motor apart and found that the harmonic balancer came apart and caused the timming chain to break. as i remember right when we were going through devils elbow 5mph zone i noticed a vibration in the boat and thought it was a new prop i was trying out come to find out it was the dampner that had come apart. it is back togther and in the boat and hope to water test next week. the only problems we found was the chain and 8 valves were bent. i thank everyone for there help.
 

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E-7 Sheepdog (ret)
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