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eng knock, partial take down, weird findings

 
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  #1 (permalink)  
Old 25 Feb 2013, 01:09 am
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Default eng knock, partial take down, weird findings

dang.

new to me 03 PT , with only about 80K on the clock, bought with annoying engine knock. I drove it for a couple tanks, changed the oil twice, drained through tight screens looking for debris ( found very little but did get a bright flake or two). Stethoscope kind of indicated the noise is lower end but was a bit muffled and hard to locate, did not sound like direct contact to block, like a crank main might.
Suspected a rod / shell issue. Didn't bother to go all the contortions to get my paws in to hook up a oil pressure gauge.

Noise is worst when 'floating' the engine ( accelerating can silence, barely keeping it at speed can silence, but under normal throttle and certain no load in-neutral , it gets loud)

Took the pan off ( pretty clean, no piles of debris) and it felt a bit like #4 rod would twist on the journal but I would be very surprised if there was enough looseness to twist it like that, so maybe just mis-interpreting rod front-back clearance or 'rod float' . Cant really judge the other rods due to balancer cradle in the way.

Took #4 rod cap off, rod shell look somewhat scored but not terrible. Plasti-gage says clearance on the lower shell is between .0015 and .002 which is upper range spec. Crankshaft #4 journal mikes just under spec, maybe .0002 small at 1.9678 , and its round ( x & y measures equal), easily within mic / reading error at this point.

The thing that drive me nuts is the parting line or interface between the rod upper and the lower cap. The interface is rough as hell, visibly uneven, maybe .010 or higher of fracture-looking topography, yet when bolted and torqued, it looks like it fits together seamlessly and all the material is tightly adhering. shees. Its almost like rod material has transferred from both parting faces to the other, but this is iron we are talking about so any transfer should not stick ! And the interface is roughed up ( unaided eye), isn't smooth up at all, so I don't think the lower cap was moving against the upper rod half, or it would burnish up a bit.

Somebody who has seen a couple PT rods PLEASE please tell me Chrysler didn't find way to "manu-cracture" a rod casting for a parting line, and that the rod OUGHT to look like every other one I have seen, a smooth & planar machined meeting face between the upper and lower sections.

Looks like I am doing a still-winter engine pull , dang. Hard to tell now whether to rebuild, possibly need a rod and a re-grind, or put a used block in , despite the junk yard wanting a seemingly insane ~$1K for a an unknown mileage engine ( I live sort of out-there in the NW 48, not a major junker center, I'll probably have to ebay or have to go a couple 100 miles for any decent selection).

Last edited by gtgt_bangbang; 25 Feb 2013 at 01:22 am.
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Old 25 Feb 2013, 04:07 am
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Default Re: eng knock, partial take down, weird findings

Since you said please twice, I won't be the one who tells you.
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Old 25 Feb 2013, 11:53 am
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Default Re: eng knock, partial take down, weird findings

The rod should appear exactly as you describe; it's the new 'cracked cap' design, it allows perfect alignment, low & precision weight and low manufacturing costs.

I'm wondering why you'd replace the engine if you've found only minor variances?

Did you check the flexplate to torque converter / clutch bolts?
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Old 25 Feb 2013, 01:27 pm
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Default Re: eng knock, partial take down, weird findings

no kidding ? Thanks for reply.

So Mopar fractures the big end to split rod after casting ? I could see the bene from a perfect fit, and nothing else made sense from what I was seeing, but I thought I was going crazy. Of course I have not measured ID of the rod end as the engine is still hanging in the car but the good plastigage reading usually doesn't lie. The shell markings didnt appear totally random or even severe, but were not really even. I'd suspect the original shells of having some slight grooving to assist oil dispersion, but again, this would be news to me - I have lived a Mopar-free life for a long time. Normally I'd expect good shells to be totally smooth.

I guess that manu-fracture method does rule out a rod re-sized with a little off the face & a re-hone.


Anyway, I have very tiny urges for buying a used engine (it would really kill this deal on a daughter's first car kind of thing and the nearest & unknown candidate is 350 miles away) but I am stuck doing all this trying to isolate a knock. I'd hate to drive a low mile engine into it's grave by racking up miles on a fixable issue.


Stethoscope is my best clue its not coming from the clutch / flywheel. outer FW bolts torque checked OK, and I don't see any abnormality / cracks through the little view space with the 'brace' removed. Noise also happens clutch engaged or disengaged too. ANd while a throttle can shift the crankshaft against its front-rear float,


I have only checked #4 rod, and mainly because thats the only one accessible with the balancer cradle still on. so I would not go as far as saying 'only minor variances' found, I just cant get at the whole thing yet.

I have not exactly pinpointed the knock noise location, kind of elusive. I wish I could hear a 2.4 with the knocky cam that is solved by chamfering a couple cam caps. I'll probably do that anyway. Sometimes I swear its top end but the cam lobes and rollers are pretty nice looking.

The dPO (dreaded Previous Owner) said the knock just showed up for no reason one day but I don't have a truth detector. It probably ran hot once or twice, as the radiator showed some seepage ( it was bent from a so called minor collision) . Compression is good and even all cylinders so I think it didn't get too bad.


so please and thanks for all good advice.


I'll be putting some info on upper front frame (load beam) and radiator support body work, I got into some of that recently too - the outer panels all looked good but somebody (dPO sister?) had a total hack shop work on it, leaving it down right dangerous, but its turning out to be easy and interesting , not too expensive , doing some limited structure work .
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Old 25 Feb 2013, 01:27 pm
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Default Re: eng knock, partial take down, weird findings

Quote:
Originally Posted by pt06 View Post
Since you said please twice, I won't be the one who tells you.
I dont understand your reply ?
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Old 25 Feb 2013, 04:10 pm
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Default Re: eng knock, partial take down, weird findings

Sounds like you've done lots of research and have good experience with bottom ends.
Rod inserts are completely conventional.
Are insert tabs rounded over?
Shells are available in .002 Oversize OD, IDK that this would allow significant honing.

The rods are forged steel BTW; using powdered steel for accuracy.

You'll NEVER see an issue with rockers- PT adjusters/rockers are a coveted upgrade for old Neon owners (not that they were bad, either)
Here's a 2.0 with 280,000, NOT at all unusual for the 2.0/2.4:



Removing cam caps will tell you if engine's been starved of oil.

The few 2.4's I've seen throw rods have been #3 and #4- Obviously observations of one guy should be taken for what it's worth..
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Old 25 Feb 2013, 07:54 pm
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Default Re: eng knock, partial take down, weird findings

oh not a rank novice on engines (youth mis-spent on Triumphs plus did a handful of bike / auto engines since ) and have some metallurgy & ceramics eng. background that told me I was looking at an novel situation regarding the rod cracked faces. Pretty cool idea if you ask me.

See no sign on #4 of a spun shell, tabs unmolested.

Thanks for the pic. These are really pretty awesome heads. I have the same clean tracks and smooth lobes & rollers on my 80K'er.
I dont think the eng was sorely neglected, hardly any crudola in it, have not seen inside the cylinder yet.

PS powder met rods aren't really 'forged', more like metal powder + a binder is pressed in to near-net shape, then 'sintered' (heated to just under melt point, to fuse together the metal grains & burn out the binder, fwiw)

Anyway , since Im supposed to see a conventional (wholly smooth) rod shell bearing, I wont sleep well until I at least replace the rod & main shells, as the one is marked up a bit, & hopefully get off with just a crank journal polish ( ever seen the shoe string + fine abrasive strip method ?). Hope I find that knock by then.

I would enjoy some brief explanation on why chamfering a couple cam caps will quiet a noisy top end, if anyone knows. I think I came across that info as a TSB but no logic behind it.

njoy, Think Spring.

Last edited by gtgt_bangbang; 25 Feb 2013 at 08:01 pm.
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Old 25 Feb 2013, 10:49 pm
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Default Re: eng knock, partial take down, weird findings

No idea, myself.
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Old 26 Feb 2013, 02:40 am
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Default Re: eng knock, partial take down, weird findings

I don't think its a bearing noise. I would cut open the oil filter and check for debris in the can [outer section]. The chain for the balancer could be loose and hitting the case. I do not know if it is possible to see it from below or to test it with a long screwdriver. The noise could also be carbon between the head and the piston. Also, check the crankshaft end play while your right there. About .003 - .010 I think. You can check neon, sebring, stratus sites for more info on your problem. This is just another reason why mechanics drink. Good luck!
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Old 27 Feb 2013, 04:05 pm
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Default Re: eng knock, partial take down, weird findings

thanks Again.

Nothing on the pick up screen, pan really good, nothing strained from oil, I didn't cut up the filters yet but bagged them in case.

Rounded up the cherry picker yesterday and break in the cold means I'm pulling it out the top next few days for a complete look see. It would be such a hassle doing the 90k belt job in situ, I figure probably a wash on the effort.

Already planning to check chain, crank thrust / float , clutch and probably replace at least the shells assuming crank is good. Compression was so rocking I hope to leave the rings & block alone, maybe false econ but dont want to spend a full resto on this one, we'll see. Can inspect the walls and feel the wrist pins once I get that far. Looks like the manual calls the piston / wrist pins permanent assembly to rod,

Wish me luck but watch for bubbles, time to pizz off the covenant nazis

Last edited by gtgt_bangbang; 27 Feb 2013 at 04:09 pm.
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