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V-8 Engine Tech

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Mopar Big Block Talk

by AndrewP » Mon Sep 17, 2018 11:49 am

Evening everyone.

So, some progress.

I removed the inlet manifold, removed the felpro gaskets either side of the pan, cleaned and re-fitted with a bead of the hi-temp gasket goop round all the ports both sides and went for a drive.
Whilst I was there I also replaced the coil as it had started to leak oil (Crane PS60) with a standard Bosch coil.

The good news is its much smoother and more oomph again so thats a major plus, but the harmonic is still there but much lesser.
It maybe that as RayR mentions, its a by-product of the manifold and at certain airflows as short of heads off and a top end rebuild, there's not much more to replace!

I think, probably not anytime soon, I`ll pull the heads, overhaul them and fit the new cam, lifters and timing gear I recently purchased whilst in the states. My only observation (and I have nothing to base this on) is that standing behind the car the passenger side exhaust 'chuffs' more than the right.
Nothing major, and 100% certain its not a misfire and nothing noticeable when looking at the engine in the engine bay (it doesnt rock or shudder) but perhaps one bank is tired or a slightly burnt valve? It pull well with no lag/stumble and so I cant really fault the engine other than the harmonic.
Dunno...picking at straws here, but Im happier now the performance is back to what I remember.

Cheers
Andrew P
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by johnw » Mon Sep 17, 2018 11:55 am

Have you repeated the test with spray to check for manifold leaks?

A compression test sounds like a good idea if you suspect the heads. I think it is worth nailing it down now as things have improved. I don't think the coil improved things. Could be worth trying the old coil to make sure the improvement was the sealing on the manifold. Perhaps one cylinder still has a bad seal round the manifold.
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by slotcarone » Mon Sep 17, 2018 9:37 pm

Burnt valves are a very rare occurrence on these engines. I have never seen one. Silly question are you sure you don't have the exhaust system hitting the floor pan somewhere causing the original problem? :)
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by AndrewP » Tue Sep 18, 2018 11:50 am

Hi John and Slotcar,

Thanks for the responses.
John,
I havent had the chance to repeat the carbie cleaner test..I`ll do that over the next few days.
I made sure the surfaces were nice and clean and flat (straight edge across them) and used a new valley pan (with the raised ridges) so Im hopeful its all sealed nice and airtight.

Slotcar...
There's no indication of anything hitting, but I`ll get the car up on the hoist over the weekend and I`ll make sure I can feel all around the exhaust and that its not hitting anywhere. It sounds like you may have encountered this problem before? Any pointers to look for?

Thanks again

Andrew
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by slotcarone » Tue Sep 18, 2018 11:10 pm

Depending on your car's exhaust system I know mine in not the original and the front pipes are very close to the floor. Just take a look to see if it is touching anywhere. The left side pipe will lift a little under acceleration so if it is very close it may be hitting. :)
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by AndrewP » Fri Oct 05, 2018 1:48 am

So, a few test drives and the re-test of the carb cleaner and its all sealed and running nice.

I do seem to get the run of bad luck sometimes as the Accel leads I purchased (and they aint cheap!) developed a fault. Cant explain what has caused it, but it looks like the Silicon they have used has a manufacturing problem and is breaking down. These leads are less than 2 weeks old BTW.

duff Accel leads.jpg
duff Accel leads.jpg (117.11 KiB) Viewed 594 times


I found them by accident at night as they were tracking at the points where the leads seem to have cracked, then tracking, and then causing some heat build-up and so on.
Id made 150% sure they were nowhere near the manifold (pointing down and routed away) so it looks like a failure of the insulation causing it. Plus its done it on 3 or 4 of the 8 leads so it looks like a bad batch.
I've sent it back to the supplier not local to me (unfortunately eBay purchase) but they have the duff leads and are looking into it/testing them and will let me know.

Anyway..Im hesitant to claim its all fixed (as it never is!) but its hugely better, smoother and has more power (as I guess its not leaking air) so Im happy with the exercise.
Unfortunately the car has started to deposit transmission fluid on my garage floor at a rate of knots now, and as Steve has suggested, its probably time to look at getting the box overhauled...just need to grown that money tree that people keep talking about!

Cheers
Andrew P
Perth, Western Australia.
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by johnw » Fri Oct 05, 2018 12:03 pm

Could brake fluid or paint stripper have got on the cables? Some thinners or other solvent?

It is tricky knowing what to replace and what to keep. On my backup towing vehicle I have replaced a couple of vermin chewed silicon leads with ones made up from bits off a scrapper, on the basis that the existing set was doing very well up to that point and is still visually undamaged.

I have a set of regular Jegs replacement leads for MOPAR that are silicon and have worked really well. The low/mid priced high volume stuff has to work otherwise they would be on the phone all day. I also find "standardbrand" blue streak parts (especially points) decent enough to last years without hassle. I note that "TOBY", has had issues with replacement/rebuilt parts not performing.

With the transmission it might be a case that simply DIY replacing aged seals, esp. the one behind the convertor, is a good option, compared to replacing the trans with a rebuilt unit that might have 100k+ on it by now.
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by Moparguy » Tue Mar 19, 2019 1:06 pm

do you know anyone with a cylinder shorting tach/dwell or scope ? will find a missfire in seconds,,,,,,,,or maybe the crank damper has spun round ?
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