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Discussion Starter · #1 ·
hello all.

Pulled the pan to check the bottom end and found something new to me. there are a bunch of tiny broken pieces of plastic. looks like a chain guide or something but not sure as all the parts are small.

I guess thats why the top end was oil starved.

Any insight is appreciated.
the good news is the bottom end looks way cleaner than the top
bone stock 390 2v

Ben
 

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I don't think the stock timing chain gears are plastic. I don't know of any plastic used inside the block, I would guess it was something dropped into the engine accidentially. I guess it is possible that the parts partially blocked the oil journals. Scary.
 

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Yup..teeth off the big sprocket. Stock ones were plastic/nylon coated to, I assume, make them quieter. Now you have to track all the pieces down. I'm not sure how to go about it, but it would probably be smart to try and back flush the oil passages somehow to get any remaining pieces out. Good luck!
 

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My advise is, drop the pan clean it out, replace the oil pump. Be sure to clean out the oil pump screen. It may not get all of the pieces but it will take care of the majority of it. Next, the replacement timing gears and chain should be all metal.
 

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I had this same plastic puzzle a few years ago with my tired 289. They are off the timing gear. I ended up dropping the pan and getting all the pieces out. It wasn't much longer after that the timing would not stay set and the resulting poor engine performance showed up. I knew were the plastic had come from. So I pulled the waterpump and timing cover and could not believe the amount of slack in the timing chain, or the amount of plastic/nylon missing from the gear. Replaced the timing set and all was good. Might as well order one now.
 

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Discussion Starter · #8 ·
thank you for all the replies.
I guess its off with the timing cover. I was rotating the motor after I took the pan off and noticed quite a bit of slack in the chain and I can see little peices of the plastic in the carbon buildup inside the timing cover. I'll add this to the list. Any recomendations on the gear/chain and gasket set?

thanks again
Ben
 

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Could it be nylon from the factory cam timing gear? ;) I agree it definitely is, and you'll see on close inspection it was originally white/natural color turned dark by too many years in dirty oil. Agreed, I would drop the pan, and disassemble the oil pump and relief (bypass pressure regulator assembly) for a good cleaning. If the engine was out of the car, I would not hesitate to pull all oil galley plugs to back-blow and flush them. While the pieces will be small that made it through the pickup screen, they're in there and can lodge odd places, causing low pressure, jammed hydraulic lifter valves, worn rockers, etc.

Having said that, I know of many engines that only had an oil change and new timing set (silent chain/link belt or double-roller), and went on for thousands more miles without issue. However, if you already had an oil starvation issue, it's a jammed oil pump relief or there's crap up in the engine, and probably won't magically circulate out. To know - if you had good gauge pressure but starvation, it's packed with crap in the engine. If you showed low oil pressure all the time, it's likely a jammed relief.

David

 

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I have a 78 F250 with a 400M that I ran the original timing chain until it hit 100,000 miles before replacing. What I did was a new oil pump, clean out as much of it as I could. Today it has 175,000 and it still runs. Granted it smokes from age but, it still runs.
 

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I did a quick enhancement of the photo to get a positive ID - take a look. Clicking on the photo top bar will blow it up bigger. One piece may be valve seal. Good point about the oil pump drive shaft - it should be checked for twist if it ate some larger pieces.
:tup:
David

They almost glow... LOL:
 

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Discussion Starter · #14 ·
Well if the gear was plastic coated before its not now. I must have 2" of movement in the chain between the gears. I can almost jump a tooth by hand. The chain will move 1/4" between teeth on the cam gear.
This gives me an excuse to clean, paint and reseal everthing on the front end of the motor.
Any preference on chain and gear sets? Gasket sets?

thanks again.

Ben
 

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Any will do, and the cheapest at the store will usually be a name brand like Cloyes. The stock one was a silent chain or link-belt type, used for durability on stock engines and for the same reason on endurance engines like NASCAR and offshore racing boats. Look how long yours lasted, and it had plastic on it! ;)

Of slightly lower mass and friction loss is the double-roller set, which is popular for mild to moderate performance engines, and was all the rage before timing gear sets, and the realization that link-belts last considerably longer without stretch. High-quality double-rollers were used for high-stress applications like Pro-Stock engines in the 1970s and '80s, and are often still used for high-lift cam engines today. Anyway, hit the local store and be sure they give you a set of either type (whichever is on special) for your correct year. You should escape under $30 at full retail.

David

Silent chain/link-belt type construction. durable, long lasting and low-stretch:



Double-roller construction example from Teague. Lighter, a hair less friction, and quality versions are often stronger with larger pins and thicker links:

 
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