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Piston Slap: An Update on Bubba and a Slappin’ Audi
Today we will update our last installment with Bubba the 1971 Plymouth Road Runner, as big things are happening to it after our initial assessment. But first, let’s mix it up with an answer to a fresh question about a topic we cover on a regular basis.
Velanesh writes:
Hi, I own a 2003 Audi TT. Recently, when the engine is idling, a type of knocking becomes audible. After comparing it to multiple engine noise problems, it seems to match the sound of piston slap.
The engine oil level seems to be fine, but should I use a different type of oil or like you said, deal with the knock and move on?
Sajeev answers:
There’s one perk to answering the same question several times on a long-running column like Piston Slap, because this gem from last September is probably the best advice:
“If the noise fades away as you 1) rev the engine and 2) listen as the motor settles back down to idle, it’s piston slap.”
If it is piston slap, check with Audi forums and VW-savvy mechanics to see if they recommend a different oil viscosity. You don’t want to switch oils and inadvertently damage another part of the motor in your quest to eliminate this annoying noise.
Now, here’s Bob’s update on Bubba:
Thank you for the response. Bubba’s interior is in very good condition, so I’m going to remove exterior parts for repair and/or replacement. I’ll be doing the work myself, so it won’t be a total repaint. My only concern is the door rust, but luckily a local shop has offered to guide me through the process of repairing.
I can’t justify putting the money into a full restoration, because it would never be worth the investment. Besides, if I make it too nice my buddy would lose our “before and after display” at the car shows!
The Piston Slap inbox lit up a few days later:
See what you made me do today?
I have been wanting to repair Bubba for a couple of years, but always got discouraged by the people who said, “it is better off original.” Thanks again for the motivation, and for giving me a clear conscience that I’m doing the right thing and not ruining it. (My job is done here.—SM)
A full restoration isn’t feasible because of Bubba being outside year round, but I will put in patch panels. I have some that I had made last year and will paint it up so it looks better. But I wish I had better skills. I’m just winging this.
Then the Piston Slap inbox struck gold:
So, I have a question for you and the experts out there. I began the install of the fender patch panel. According to what I’ve read and seen, the weld is made up of a series of small welds to avoid too much heat and causing warpage to the panel.
My question: Do I keep welding and grinding until I have filled in all the spaces between welds, or do you finish off the spaces with Bondo?
I’ve attached a photo of what I’m talking about. I actually did another pass on welds after taking the picture.
Sajeev answers:
I am far from an expert in body repair, but the less body filler (like Bondo) you use, the better. But the patch panel must be fully welded into the fender. From there, grind down the welds for a smooth finish. Having gaps in the metal just invites moisture and rust, especially since Bubba has to sit outside.
Chasing perfection is a noble endeavor, but it can drive you crazy: Flawless finishes use less filler and you’ll spend more time perfecting the sheetmetal with traditional hand tools. I have heard that not using any filler is possible, but that seems like a lot of labor for most classic cars.
Don’t worry, Bubba will be just fine with the effort you are putting into it!
Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.com—give us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.
On the Audi how many miles. If high miles it could be a chain tensioner or stretched timing chain. Neither are cheap.
The thing with Audi and BMW things start to go at 100k miles. It can get expensive.
Piston slap at idle coke generally hoes away as it warms up. Rev’d cold it will still knock.
I would just have it checked professionally as it can get even more expensive if timing chain issues.
On the Plymouth. Are repo fenders avail. Often it is cheaper to replace than repair. Doing this on a car myself.
A quick internet search…
-inner fenders, 71 Duster Fenders, are all reproduced but not these ones
-posts complaining that no post-70 bigger B-body Mopar fenders are out there (but these were 10 year old posts)
So maybe they are available now, but the algorithm is not putting them to the forefront.
Satellite fenders are the same apparently (hood and grill are different for Road Runner front end in 71) so finding a good used may be possible with a wider search?
Owner’s work is looking good anyways, but if not happy with the result finding a used one shouldn’t be impossible.
Yes a Satellite to a road runner is like a Lemans to a GTO.
Just always best to go with new metal if you can find it. Mopar I know is not always the most reproduced.
The time put into fixing things like this make a new fender cheaper if you can get it.
Yes the bead needs to be high on the weld so you can grind it flat. You should need no more than skim coat of filler
The Mopar picture at the top is quite nice.
Leading those small areas could be a good alternative to welding. No
That is what Bondo is made for. I am not a body man by any stretch of the imagination, but I try to leave a little crown on my welds so I can grind down to relatively flat. You’ll never get all of those little divots out unless you are a pro with your 10000 hours under your belt – and probably not even then
Use good body filler, like all metal, or kitty hair to fill all those little voids. Then you can go over that with a filler that is easier to sand, like feather fill. Not that I’m an expert or anything. I like to use a selfetching primer or something designed to seal the metal and keep it from rusting.