41 Plymouth SB Mopar Engine Swap

So it's in the engine. Ugh!
With an old 'scope you could do a cylinder balance test, but it's smooth at idle, so I expect that it would show even compression. This also means that the carb idle circuits are good and there probably is not a vacuum leak.
Things I've seen that cause this:
Try bringing up the idle to where it gets rough (1500-1800 should be close to fast idle cam speed when warm). Try richening the carb a bit on each side (either cover with a rag or squirt some carb cleaner in) to see if you have a transition circuit or main circuit issue.

I've also seen weak valve springs cause this, but they were old, not fresh. The oscillations at idle they could handle, but not at 1800 RPM.

Disconnect the vacuum advance (if equipped). I've seen a strong advance curve (vacuum and/or centrifugal) cause this. You can also rotate the dist. a bit (at the rough speed) to see if it helps.

Hook up a vacuum gauge. See if the vacuum gauge fluctuates (it probably will). This tells you it's in the top end, not compression, provided it's smooth at idle.
Hook up a timing light. See if it jumps when rough. This would indicate an ignition problem (spark scatter or trigger problem). This could be as simple as a poor ground, or bad cap, weak coil, bad gap on the dist, bad pickup, or bad EI box.

BTW, you should be able to remove the entire front clip as a unit unless there were big changes done to the mounting. Drain the radiator and disconnect the hoses. Remove the hood, bumper, rear fender bolts and the bolts below the radiator yoke. Remove stuff attached to the inner fenders. Tape up the paint around the back of the fenders and disconnect any fender struts. With a friend or two, lift the front of the fenders up, carefully spread the rear of the fenders, lift the clip and walk it off forward.
1942 shown, but very similar. Yes, I cringe even mentioning this, but with a lot of care, it can be done. I've had my '40 clip on and off many times, but it isn't freshly painted.

 

Thanks for all the suggestions. Timing is rock steady, no scatter. It is a new mag pickup distributor, so I assume the reluctor is ok for all 8 pulses. I have richened the cruise mode jetting to eliminate a cold stumble, which it did.

I would love to get it on a scope to assure myself it's not ignition but I don't know where to find one. I will try your suggestions.

I CRINGE to think about removing that front end, too. There is a lot of wiring that has to be disconnected and pulled back, in addition to your list. I hope it doesn't come to that.

What's the chance the clutch is out of balance?

 

Clutches are built to be neutral balance. They are very rarely off. Assemblers would go out of business pretty quickly if they sent out junk. They normally don't pay labor to DIY guys for warranty work, but they either pay shops or don't sell another one ever again if the shop has to eat it.

I kind of doubt it's the dist. either, but I'd guess almost everything is new or rebuilt on this, so something snuck out the door and into your build...
Gap should be .008", checked with a brass (non-magnetic) feeler gauge, IIRC. I have seen bent shafts in new dist. Check gap at each tip. I've seen wher ethe vacuum advance pulls the pickup plate and changes the gap a LOT too. Yours doesn't sound like that, but it's another reason to check with the vacuum disconnected.

If you have another EI box around, do the old "swap with a known good unit and retest". Same with the coil. Make sure the coil is wired properly. Some REQUIRE a resistor, some REQUIRE full 12 V. Swap out the resistor too, if equipped. Check all connections.

A jumper wire with alligator clips can be used to connect grounds to check for that. Battery - to block, battery - to frame, battery - to EI box. I've even used jumper cables for the big jumps (first 2 listed) just to make sure the grounds are good. That usually causes slow cranking and other strange electrical problems, but poor grounds are common in fresh painted builds, and the EI pulse is very voltage drop sensitive.

Yeah, 'scopes are so old school now. Distributorless Ignition Systems (DIS) are across the board, and the typical tech just replaces stuff until the problem goes away. Try old school shops, especially if they work on old (non-diesel) trucks. Even most trade schools don't have them any more. Is there a race shop (Engine, drag or short track) nearby? How about a motorhome shop with a dyno? The retirees with a gas MH want every bit of MPG they can get. This is the sort of place that still values a 'scope.

If you have local car buddies, maybe you can try another carb too. Anything reasonably simple to avoid pulling all your work apart!

P.S. Can you write up again what the engine and accessorizes are, so it's all in one place instead of 25 pages?

 

Pulling the clutch and taking a look would be a lot easier then pulling the front clip and the motor. At this point, I'd drop the trans in a heart beat. It would have to come off to put the motor on a stand anyway.
A clutch disc with a spot of oil or grease could give you a clutch vibration. The amount of clearance between the clutch pressure plate and the bolts that hold it in place may offset the pressure plate enough to give a slight vibration. I think I would also look at the trans input shaft bearings, slop in the front bushing, or a defective throw out bearing can all give you a vibration. an out of round clutch disc would cause a problem as well. With the trans in neutral, the input shaft and the entire clutch assembly is turning with the motor, with the clutch pushed in, the flywheel, pressure plate, and the throw out bearing all are spinning with the motor. Gene

 

Gap is right. Distributor seems very nice and tight. Will put it on distributor machine tomorrow just to verify. Voltage to ignition is right. Vacuum is great. Ignition advance is working. The thing starts better than any of my other cars. Same result with vacuum disconnected. No missing clutch bolts. Richening mixture doesn't change it. If it quacks like a duck.......

Gene, I can't pull the transmission without a LOT of work. Almost as easy to pull the engine. Besides, I am convinced it's a balance problem.

 

I remember you had to modify the motor mounts a couple of times, you don't have a motor mount shifting around a little do you?

Its going to suck to have to pull the motor, but your nearing the point you have little choice. Once its out, I would still look at the clutch/trans 1st. A motor balance issue is pretty far fetched these days, but mistakes do happen. Sorry, Gene

 

I used the donut type motor mounts, Gene. They aren't moving. I suspect my machinist screwed up somewhere along the line. Thanks.

 

And so the next chapter in the adventure begins. It wasn't as bad as I feared it would be. Extraction tomorrow.

 

What's the plan?
Engine stand run-in with machinist/balancer in the house?
Disassembly and recheck?

 

Ok, guys. More help needed. I'm pretty sure I found the problem. After separating the tranny from the engine, I noticed that there were a couple of small chunks of metal broken off the pilot bushing. After further examination, the pilot bushing was "wallowed out".

I took some measurements and it appears I have installed the wrong pilot bearing. I only have about .200" of engagement and most of that is tapered, thus the "wallowing out" and the clutch shaft would get off center, so that would cause the imbalance problem.

Attached is a picture of the crank end. As you see, it has a bushing in it but is machined for a bearing. Any idea which bearing I need? Are there any other things I'm missing? The clutch is hydraulically actuated and I got the linkage and the master cylinder pretty darn good, so it works fine.

One last question. I may have screwed up the transmission input shaft. It has perceptible play in it. I haven't measure the deflection but I would say .030 - .050" at least. Is that normal for the AX-15? Or am I going to have to have this new transmission gone through?

I guess the good news is that my engine may not be the problem.

Thanks for your help. We will get this right. Pioneers get a lot of arrows in their chest. All mine seem to be sticking me in the ass.

 

You need a timkin fc69907 pilot bearing with an AX15, it fits in the big hole in the end of the crank.
Any way you can run the engine without the transmission hooked up? This will positively isolate the transmission/clutch as the vibration culprit.

 

Will this pilot bearing work? It's for a '98 Dakota 3.9.

https://www.oreillyauto.com/detail/...998/dodge/dakota?q=Clutch+Pilot+Bearing&pos=0

 

I don't have an engine stand for running the engine but I'm going to try to find one.

 

Yep that's the one

 

Once you remove the bushing, try installing the trans/bellhousing to engine and check depth of input shaft into the crank. No need for the flywheel here. Mark flush with the raised section shown, or if you can reach it, the actual opening. Make sure the trans input shaft will be supported enough AND does not bottom out in the crank.
You can also make sure the input shaft does not bottom out on the bearing before bolting it all back together.
The trans is probably okay, but it would be a good idea to swing by a local shop and have the guys that see them every day take a look. A 6 pack on Friday afternoon would probably get a good inspection. The input shaft bearing would be the main concern, along with the seal. A 98 Dakota 3.9L seal is under 10 bucks, the bearing is 44 bucks. Cheap peace of mind for my money. The reason the shaft is supported in front by the crankshaft is the weight and power through the clutch and so any runout is taken up. The input shaft normally has a small amount of play for this.

Did the flywheel have the offset holes for the external balance?

I'd really try to have the engine, bellhousing and flywheel without clutch able to start and run for a minute or 2. A bunch of 2X4s nailed into a framework would prop it up enough to check, if nothing else.
Maybe bolt the engine in the frame and support the back of the bellhousing and test that way.
2 minutes without water or exhaust won't kill it. It also looks like your picture was taken sideways from under the car. Looks like Gene is right again!

 

Can the shaft and bearing be replaced without disassembling the transmission? Flywheel does have offset holes and has been lightened and then balanced to the rotating assembly. It is a 3.9 flywheel.

I'd already decided to do what you describe to try to test the engine before buttoning it all back up. Thanks!

 

I had a pilot bushing fail like that on a 360. It turns out the cause of problem started with Mopar cast crankshafts not being finish machined for a pilot bearing. I forced a managed to make a bearing fit, but it didn't last long. I may have damaged it installing it, who knows. With the input bushing bad, the only thing supporting the input shaft is a single bearing, so that may well be your vibration.The bearing posted above is what you need, and test running with it apart is a wise plan.

 

Probably old news, but yes, the input chaft bearing on the trans can be changed by removing the front cover. If I remember right, there is a snap ring holding the bearing in place once the cover is off, but its been a while. I may be confusing that input shaft bearing with something else. Gene

 

These say it's not easy.
https://www.jeepforum.com/forum/f12/ax15-input-bearing-removal-888271/
https://www.wranglerforum.com/f218/front-bearing-on-input-shaft-ax15-808913.html
video, front bearing at 7:30, but NOT removed. It does show play...

 

I rolled the dice. I haven't put many miles, less than 400 miles, on it. If you look at the deflection, it is minimal and the transmission is new. Plus, it wasn't unsupported for all those miles. I put the new pilot bearing in and I have plenty of shaft engagement and no end loading on the crank. I will crank it up tomorrow for a few minutes before reassembling the front end and keep my fingers crossed.

 

Cranked it up today and it's smooth as butter! Yay!

 

That’s good news - hope it stays smooth on the road!

 

That is a relief, and its not even my car! I hate to see really neat projects with so much time and effort invested go south because of a simple part that turned out to be defective. Gene

 

Great news Rock! phew

 

Actually, it wasn't a defective part. It was the wrong part. I selected a pilot bushing and the shaft did not engage it adequately. I replaced it with a pilot bearing that moved it up on the shaft adequately and supported it. Hot rodders learn a lot of lessons the hard way. At least I caught this quickly. The correct part should look like this.

 

Ok, I'm finally getting some progress on the interior. Got the trunk panels today and should have the door panels this week, now that we have carpet and binding. Can't wait to finish this up.

 

That is a really nice ride, much better then anything I could ever own. I'd ruin it too fast. Gene

 

A few more interior pics. Next up is headliner and carpet.

 

Reading your post I see you have changed from the oem steering to a rack and now a snub with mustang type front suspension. I'm gathering parts for a 39 Plymouth coupe that I only drove one time with the six still in it. Liked the way it drove so just wanted to know why you kept making the changes to the front maybe I missed something.

 

Well, the original steering has unequal tie rod lengths. The short side will exhibit more roll and bump steer, plus the camber and caster adjustments wouldn't work for me with the suspension lowered and with radial tires. So, I ditched that, as well. The stub gave me lots more room for mounting everything, works better for my purpose (interstate trips through the mountains) and is just a cleaner install. That is why I did it. YMMV.