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Discussion Starter #1
Hi guys. Looking for some ideas on my 65 289. I’ve been restoring the car over the past year, and in the process had the engine and transmission out for cleaning up and taking care of the engine compartment restoration. The engine ran well with no issues prior (other than a bad oil leak). I elected to just Overhaul rather than rebuild this one completely. I checked the main bearing clearances, which were within spec, replaced the timing chain, oil pump and pickup, gaskets, and cleaned/repainted the engine for re-installation. I reused the original pushrods and rocker arms, and kept them sorted to go back into the same bores. I primed the oil pump a few weeks ago, and Today was finally the day to test fire it. It took off quickly and idles well, but I have quite a loud knocking sound that gets louder on revving the engine. It sounds like it’s in the lifter valley area, but it’s difficult to tell. I re-adjusted the rocker arms, which did need a partial turn after heat cycling, but the noise is still there. It does not sound good, and I certainly wouldn’t be comfortable running it for any length of time like this. Just wondering if anyone has a quick idea of what I may be overlooking. My instinct says that perhaps a lifter went bad in the process of sitting dry outside the engine, and is now causing a loud tap on the cam. I’m going to try to post a short video to help you out. Thanks for your time.
 

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Maybe a piston is slapping something?

I had a sound like that once and it turned out to be a blown head gasket. The sealing ring on the head gasket in one hole blew into the cylinder (was still attached to the head gasket) and the piston was smacking it.




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I assume you had the engine out of the car and the trans separated from the engine?
Sounds like something going on between the converter and flexplate to me......
Or.....
Oil pan was off? It's now being hit by the crank..... somehow,
 

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Were the engine and trans separated when you worked on the engine? If the engine didn't make noise before, then your issue has to be something to do with the pickup tube or possibly a bearing cap that didn't get torqued done.
 

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Discussion Starter #10
Yes guys, the engine was out and separated from the trans. In fact, I converted this car from 3-speed manual to C4. It has a new flex plate, oil pan, all stock components, nothing modified from factory. It doesn’t resist turning over by hand, and it really doesn’t knock like that when cranking it, and it’s almost gone at slow idle, but any more than that, it gets much louder.
 

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Kelly, is your timing cover on correctly ? A slightly too far forward timing chain cover can get smacked every rotation by the counterweight on the back of the balancer. Sounds just like that. Whats your oil pressure like ? LSG
 

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Maybe a piston is slapping something?

I had a sound like that once and it turned out to be a blown head gasket. The sealing ring on the head gasket in one hole blew into the cylinder (was still attached to the head gasket) and the piston was smacking it.




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Are the exhaust pipes banging on the body somewhere?
Could also be torque converter bolt hitting the flex plate. Pull the inspection cover off and have a look.
 

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Are the exhaust pipes banging on the body somewhere?
Could also be torque converter bolt hitting the flex plate. Pull the inspection cover off and have a look.
Good suggestion. Had a CTS-V I replaced the motor in. When I had it all assembled and running I got a tick albeit not nearly as loud as yours. Turned out I forgot to fully tighten the torque converter bolts.
 

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Sounds like a piston hitting a valve. I had the same thing happen when a keeper broke and dropped the valve down into the piston so the piston would keep smacking the valve every time it came up to TDC.

Others have stated some easier fixes that can be checked off before you go tearing the motor apart again but that may be what you need to do. I hate giving bad news like that but there should be evidence of this (in my case, the valve put a nice new shine on the top of the piston). I hope you have a magnetic drain plug because you should probably be finding metal shavings in the oil pan from whatever is doing this.
 

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Sounds like something rubbing to me. Get a mechanics stethoscope or long screwdriver or something and listen for where the noise is coming from. Possibly something rubbing the flex plate? Loose torque convertor bolts?
 

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After giving this some further consideration and the fact that you only basically replaced gaskets, I’d start looking at all the bolts you DID remove and reinstall. Probably not a valve slap like I originally thought if all you said is correct, so I’d start looking at things you may have forgotten to tighten up. Start torquing.
 

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Assuming it's not a rod or lifter knock (if it is engine internal sounds more like rod than lifter because it's deep and loud) try this....

Here is something you can check on-car without disassembling everything. Unbolt the C4 flexplate cover. Rotate engine manally by hand and inspect each torque conv bolt position and see if you can locate the drain plug. See if your torque the converter is contacting the drain plug. If it is loosen all and rotate until drain plug is aligned properly.

Since you are new to C4 converting from manual you may have done this as I did.....check to make sure that the torque converter drain plug is coming through the hole on the flexplate that it is supposed to poke through. I made this mistake on my C4 when I installed it (bought the car w/drive line taken apart) and even though I never ran the motor with that error it did coc the plate sideways and leave a small 'ding' on the plate. I corrected it and it later fired up. Probably not related to that but I later had to replace my converter because it was shaking badly out of balance. Could have been the incident that caused it but I doubt it. It never had a knock but as I said I never ran the motor with the plug smashing the plate. So check that...it's an all too common error when slapping the C4 and converter back on.
 

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Discussion Starter #19
Thanks guys. I’m starting to wonder about the converter drain plug. I don’t remember looking for that when I tightened the nuts, just that the studs were coming through the flex plate. I’ll check that first, then I guess I’m pulling the oil pan. I DO remember retorquing my rod caps, but that doesn’t mean I couldn’t have somehow missed one. I’m just wondering if that’s the case, what damage I’ve done in running it for a few minutes. I’m afraid to drain the oil and see any signs of metal shavings. Oh well, I guess I have to face the music. Thanks for the suggestions.
 

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Let us know what you find, I’m very curious. Also, I don’t believe all torque converters have a drain plug. I don’t recall seeing one on my B&M when I installed it but that’s been 13 years ago.
 
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