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08-10-2022, 08:04 AM | #1 |
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8BA cam position
I developed a loud knock in the lower end of my 8ba. To eliminate any valve spring problems I pulled the intake and checked for broken springs and checked the valve lash. Everything was within a couple thousands and the springs looked good. I then pulled the pan and checked the rod caps all are torqued to 42- 45 lbs., there is no movement that I can tell except side to side, which is required. I noticed the camshaft is not centered in the bearings, it's pushed to far to the back of the motor. This can't be correct. I also don't think this is the source of the knock. Any ideas??
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08-10-2022, 05:48 PM | #2 |
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Re: 8BA cam position
For the cam to move rearward, the cam gear bolts would have to come loose. Not sure if you can see anything through the distributor hole. Other than bearings, flywheel bolts are a possibility, as would be piston related problems (although more likely a "top end" type noise). No metal or odd stuff in the bottom of the pan?
Terry
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"It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302 |
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08-10-2022, 07:06 PM | #3 |
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Re: 8BA cam position
Can you get someone to turn the crank while you watch and listen from below?
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08-11-2022, 07:10 AM | #4 |
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Re: 8BA cam position
Are we in agreement the cam has slid back?
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08-11-2022, 07:26 AM | #5 |
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Re: 8BA cam position
I don't necessarily believe it has slid back. About the ONLY way that can happen is for the front flange of the cam to wear excessively and/or the front of the block to be worn off (the thrust face for the cam). If never seen either happen, though I have seen a case where the cam bolts were too long and ground into the thrust surface a bit.
Did you happen to use repop cam bolts or a repop cam-bolt-locking plate (which are sometimes thinner). Also, if anything like the above happened - enough for the cam to move, then there would be some obvious metal in the oil pan - a LOT. I'd check that out. Also, I noticed the cam lobe in the picture appears in about the right place on the lifter. Probably chasing a ghost at this point in time. |
08-11-2022, 07:28 AM | #6 |
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Re: 8BA cam position
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Last edited by Bored&Stroked; 08-11-2022 at 09:13 AM. |
08-11-2022, 08:47 AM | #7 |
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Re: 8BA cam position
Look at the lifter and how it appears to be centered over the cam lobe.
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08-11-2022, 09:15 AM | #8 | |
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Re: 8BA cam position
Quote:
I didn't rebuild the motor. The previous owner Gerry Groswold is deceased and had the car for 30 years. I've had for 9 years I'm not sure when it was rebuilt. I didn't see and metal in the oil and it was fresh. I'll look at it again. The cam lope is not exactly center in the lifter. Maybe it's been like this from the beginning. To me the cam should be center in the bearing. |
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08-11-2022, 09:18 AM | #9 |
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Re: 8BA cam position
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08-11-2022, 09:19 AM | #10 |
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Re: 8BA cam position
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08-11-2022, 09:21 AM | #11 |
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Re: 8BA cam position
Also, if the sound was sort of a LOW sounding knock - which changes tempo with engine RPM, I've never heard that out of the valve-train - that is usually the lower end.
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08-11-2022, 12:07 PM | #12 |
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Re: 8BA cam position
It was differently loader down low by the pan. I suspect it's lower end also. But the cam location has me concerned.
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08-11-2022, 01:34 PM | #13 |
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Re: 8BA cam position
I'd be extremely surprised if the perceived cam position is an issue - have never seen any issues in this area, with motors in ALL sorts of conditions.
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08-11-2022, 02:41 PM | #14 |
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Re: 8BA cam position
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08-11-2022, 02:47 PM | #15 |
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Re: 8BA cam position
The lobe will not be centred. Being offset promotes lifter/valve rotation.
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08-12-2022, 11:44 AM | #16 |
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Re: 8BA cam position
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08-13-2022, 06:00 PM | #17 |
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Re: 8BA cam position
So I tore into the motor today, removed the rod caps and plastigauged the gaps on all, everything is .002 even one of the main caps was .002. Still no sign of what would cause a knock. I cut short pieces of hose and installed them on the rod studs to protect the crank. Then pushed the piston up in the bore to check for any movement in the wrist pins, there is not any slop that I can tell. Looking at the rod bearings there is some wear, should I replace them even thou they gap well with in specs?
I also noticed the rod cap nuts have a groove around them that were facing up when install. What is the purpose of that? |
08-13-2022, 06:15 PM | #18 |
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Re: 8BA cam position
Not knowing anything about the specifications of the motor when it was built. I assumed it was a plain Jane stock Ford 8BA 239cu in. The previous owner had a single 94 carb and a stock distributor. I was pleased when I measured the stroke on the crank, it's a 4inch Merc. I can see the stamp on the camshaft it's an 8CM.
Rods are 8BA. M-19 oil pump. The cylinder bore measured 3-1/4" Pleasantly surprised. |
08-13-2022, 07:06 PM | #19 |
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Re: 8BA cam position
Keep looking till you find something out of spec.
If rod bearings are not destroyed, look at the mains and the thrust. As long as it is apart, replace the rod bearings as cheap insurance. ONE VERY IMPORTANT THING, NEVER USE PAL NUTS ON ANYTHING AUTOMOTIVE. They are a recipe for disaster. Use Marsden nuts.. OEM's do. |
08-14-2022, 08:23 AM | #20 |
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Re: 8BA cam position
Just use small block chevy rod nuts they work fine many on the barn have used them.There is no difference in how you use them and don't require anything else just install and torque them,45/50 ft lbs same as ford specs.
R |
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