Help ID-ing this rattle

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seabiscuit
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Re: Help ID-ing this rattle

Post by seabiscuit »

Due to it being little league season extra time has been hard to come by so the going is slow.

Thanks for the info on the rubber part and shims as I never took that close a look at the tensioners before. When i first saw it i assumed it was a seal. Since it was partially dislodged, it created a space between the 2 remaining shims and I believe this is where the ticking came from when running. So my plan now is to first test the unit and then if all is ok get another nylon washer and fit it in similar to the space the rubber took up. I'm thinking since all was ok before the failure, it should be fine if I space it the same? I'll use JT's 1/16th as a reference.

Any other tips on tensioner removal is appreciated so there are no surprises. I was going to follow the recommendation on the DatsunParts website where he suggests zip ties to compress the unit.

Both upper and lower shoes show little to no wear. Gear teeth look pretty good but I'll post some pics when i can and maybe get some feedback on what it looks like to you.
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Re: Help ID-ing this rattle

Post by jrusso07 »

Definitely put the zip tie around the tensioner to keep the spring loaded foot with the body. Leave a long tail on the zip tie and use it to removed the tensioner.
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Gregs672000
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Re: Help ID-ing this rattle

Post by Gregs672000 »

Well, for me the zip tie is optional. It probably makes install somewhat easier, but it's really not hard and the spring is not that stout. You can get nylon washers at most auto parts stores, check in the oil area as the 9/16ths (I think it was) washers fit PERFECT over the shaft. Having it super tight or to some "spec" is not critical. What you don't want is to allow the tensioner full range of motion, which it WILL DO if there is no shim and no oil pressure. At certain points in the engine rotation the tensioner would completely compress, the crank would move but the top end/cam WOULD NOT. That gets quite scary, especially when your running high compression pistons, bigger valves and a high lift cam! It's not just an annoying rattle: Cam timing is way way off, pistons are moving and valves are down! I used to think that if I spun the engine with the starter and no spark before firing it I was ok (brings up oil pressure before starting the engine, I do this with a kill switch), but the reality is cam timing is jumping all over the place while I'm cranking it... bad!

You MUST make sure the tensioner is getting oil pressure (see earlier posts on how). It should not have been able to retract as it sounds like it was when there is oil pressure to it, so you either observed it without oil pressure being up in the engine, or the tensioner is not working correctly. I lean towards the latter for reasons unknown at this time because it was doing it while the engine was running before. Clearly the PO installed shims, which means the tensioner was removed, which means that they may have installed it incorrectly and covered up the oil feed hole. It was not obvious until the rubber washer failed and the tensioner was no longer as extended. With no oil pressure to keep it tight, it was slapping around and changing cam timing. With shims a lack of pressure at start up and subsequent cam timing issues are minimized, but I still think the tensioner should be pressurized to take up any slack while the engine is running. It is my understanding that many engines use ratcheting mechanical adjusters so oil pressure is not an issue. With enough of the shims on ours that may be true, but I prefer to have just a little bit of movement as I feel it was designed that way.

What is clear is that ANY U20 should have the tensioner shimmed whether it's allowing the chain to hit the evil L or not. Not sure if that is in the wiki when discussing the evil L and shimming the tensioner.
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Re: Help ID-ing this rattle

Post by seabiscuit »

Is there such a thing as "over shimming?" I ended up adding 2 more shims to replace the failed rubber piece. The shoe still retracts, but I don't want to have too much tension on the chain. I drained the oil earlier and pulled the oil pan when I was inspecting the lower components before I found the culprit, so oil pressure wasn't too good when I was turning the engine over and watching the tensioner pulsate.

It also turns out that the PO had the gasket on backwards and the oil passage was blocked. Maybe the shims and rubber compensated for the lack of pressure.

BTW, the shoe has absolutely no wear on it. It looks brand new.

Once again, I ran out of time today and had to do family home stuff so hopefully tomorrow I can put the open parts together and run it.
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Re: Help ID-ing this rattle

Post by JT68 »

1/16"-1/32" free play is fine.
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Re: Help ID-ing this rattle

Post by Gregs672000 »

I'm no expert, JT68 much more experienced than I. Pretty sure you have it right; the shims were saving you until the rubber one failed. You should be fine now. I was not sure what your mechanical or specifically U20 knowledge level was, so I hope I didn't sound condescending or anything! Glad you have gotten this fixed, onward!
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Re: Help ID-ing this rattle

Post by seabiscuit »

IMG_0156.jpg
IMG_0149.jpg
No probs Greg! No bad feelings at all. I am learning this motor as I go along. Many times explaining things at the most basic level is the best. I'm far from a weekend warrior mechanic. It definitely helps me understand and learn how things work. I appreciate everyones help.

I did get to observe the tensioner working with the motor running. The chain seems moderately taut now. Like i mentioned earlier I hope not too much from my added shim. The tensioner does have 1/16th to move. So I imagine with all the lubrication going on there the pad will last quite a while bumped up to the chain? And now that the oil hole has been liberated I'm surprised this was my first problem with it.

Here's a couple pics of the shoe and the cam gear for your wear opinions.
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Gregs672000
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Re: Help ID-ing this rattle

Post by Gregs672000 »

Cool, I'm glad... Nothing frustrates me more than not having enough information to do the job or to have to guess at stuff without understanding what I'm looking at. I do tend to get a bit verbose sometimes though...

The tensioner foot looks good. The gear shows some signs of wear, but I don't think it's bad enough to warrant replacement yet, but others may differ. With the evil L still being in place, you need to check the bottom of the L for chain strikes and make sure it's still OK. Otherwise, we may want to cut it off or at least be monitoring it. Also, I note that there is no locating dowel pin on the cam gear. Is this an adjustable Gear? If it is, the bolt hole slots will be oval. Just remove or back out one bolt and look. If it is, I would reinstall the bolts with blue locktite just to be sure they stay put. If you were happy with the car and where it was making power in the rpm range, leave it alone... it's probably timed just fine (referring to cam timing here).
:smt006
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Re: Help ID-ing this rattle

Post by seabiscuit »

Just wanted to say thanks again to everyone for your time, suggestions and help. In the end it was a simple fix for a 50 cent part, but at least i got exposed to this part of the engine and how tensioners work.

Bottom of L untouched, and it looks like the rough edges on the retainer clips were from PO bending them back to guard the bolts.

Thanks again all!
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Re: Help ID-ing this rattle

Post by Gregs672000 »

Yeah! Beats the hell out of pulling the head! We're happy to help... it's family Here! I love these people!
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Re: Help ID-ing this rattle

Post by Geistfahrar »

I am jumping onto the end of this thread ( as opposed to other chain-rattle threads ) since it contains many pertinant comments on shim installation, & I need to "take exception" to Dean's instructions on the shim-kit installation. First off, I cannot run the engine for 10 to 20 seconds, as I have pulled all the cooling parts and the alternator off the engine. I don't want to re-install the radiator until I have it flushed & painted, & I would rather wait to do the GM alt swap & rewire until I get the shims in.

Dean wrote " measure the distance with the tensioner fully extended --- add shim washers to take up the difference ". Unless I missed something, that would leave no gap for movement. Most posters have said, 1/16" movement between a relaxed & extended tensioner is sufficient.

To re-assemble the engine so I can start it, I would have to flush/paint the radiator, buy /install a reman GM alt & buy/install the GB dizzy ( smog is off & boxed ) before doing the shim ( easiest task ) install. Greg's first post on April 18 to this thread gave me the hope of a much simpler solution as to the number of shim washers to add. I went back out today, and rotated the crank by hand, through enough cam cycles that I could observe & measure the distances between the back of the shoe and the body. I found that the gap, under spring-pressure alone varied between 7/32" & 9/32". At the farthest extension, I could not manually move it any further with a screwdriver against the back of the shoe. When I rotated the crank to the point that the chain relaxed, the shoe would snap back, completely against the body, then the spring would extend the shoe with a 5/32" gap.

If my measurements ( and assumptions ) are correct I should add 7/32" worth f washers to the shaft, to reduce the total travel to 1/16". If I am off-base, please advise, so I don't screw up.

Thanks,

Garry S.
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Re: Help ID-ing this rattle

Post by cktrap »

If the engine is hooked up except for the cooling and alternator you can run it for a little while. 30 seconds is fine. Sounds like your looking for oil pressure. All good
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Re: Help ID-ing this rattle

Post by JT68 »

You are correct. There is no need to run the engine at this point.

If you make it so the maximum gap (free travel) under any condition is 1/16" it will be happy. That max gap will occur any time the cam is beginning to open any 2 valves when rotating the crank CW. (in that case the "non tensioner side" side of the chain will be maximally tight and all the slack will be on the tensioner side)
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Re: Help ID-ing this rattle

Post by Geistfahrar »

Thanks JT,

The plugs are still out, VC loose & socket/wrench on the crank. Will turn a few more ( cam/valve ) cycles tomorrow & pay close attention to cam-lobe positions when shoe moves to full extension.

Garry S.
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Re: Help ID-ing this rattle

Post by Geistfahrar »

Per TJ's instruction, I rolled the crank over several cycles, observing shoe extension vs. cam-lobe position, & verified the maximum extension to be 9/32". Dean's (6) shim washers ranged in thickness from 0.083" - 0.088". If I add the two thickest shims to the shaft, it will limit the travel to 3/32". I will report back, after I get all the new stuff ( and the old radiator ) back on the car, & fire it up. I won't take her out on the road, however, until I change the oil & filter, & bleed/test the brakes.

Thanks to all,

Garry S
Location Southern Cal
69' 2000 Roadster, being repaired by O/O
2001 Mercedes ML430; Was Wife's ride, now Grocery-hauler
2005 Jeep Wrangler X; Was Motor-home Toad, now local shopper
2005 33' Dolphin motor-home; Was vacation home, now guest house
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