I would verify cam timing before I pulled the engine. Put a degree wheel on it and check it.

It's more than a vibration, it's the run on that's the bigger issue.

I’m aware, I think it might be a timing issue, but could be caused by the jetting in the carb. What I was wondering was if he has a weak cylinder that could be causing the vibration.


OP, I know this is going to sound off the wall, but do you have another carb you could swap and see how it runs?

I've done a compression test-
1- 215
3- 215
5- 210
7- 215
2- 215
4- 215
6- 205
8- 210

I've actually never heard of a running compression test.

I just replaced my original Muncie M21 with a brand new Autogear M20. I have not had the clutch off, but I feel that's the root of my problem. The rotating assembly was originally balanced with a flex plate. I also got to see, in person, the engine running/revving on a stand before I bought it and it ran normal with the flexplate at that time. I removed that and installed a new flywheel and McCleod clutch, which in theory, should be plug and play since everything is externally balanced. But, I think that is not my case.

I originally had a Holley 830cfm carb and replaced it with a new Holley 750cfm over the winter.

Frankly, I've reached my limit with the unknowns of this engine. I don't know the exact piston spec or the exact compression ratio, etc. I'm ready for a known engine so I can enjoy the car.

This whole deal has been beneficial though because I've learn so much from everyone's help and the troubleshooting research I've done. :thankyou:

Daniel

Well if it ran good before and all you changed was the flywheel and pressure plate I’d pull that off and have it balanced. Good time to run it without the flywheel too. Was it a McLeod flywheel?

It would suck to build a new engine and find out you still have a problem.

It's a PRW flywheel. I spoke with PRW and McCleod and they both said the flywheel and clutch I have should be compatible with each other in terms of balance.

I considered having only the pressure plate and flywheel balanced, but from what I understand, you have to balance the whole assembly for an accurate result- balancer, crank, rods, pistons, flywheel, and pressure plate.

I'm not sure how I'd start the engine without the flywheel.

Daniel

Static compression numbers look good. I ask about a running compression test because I've seen lifters collapse when running a few times and you'll have 7 good cylinders and then one real weak one.

Did this start before the carb swap or after?

Do you have the flex plate that you saw the engine run with? Or just any flex plate for that matter? I'm wondering if the flywheel being a lot heavier then the flex plate is making the vibration worse and its actually been there the whole time, you just couldn't notice when on the stand.

The vibration was there before the carb swap.

Unfortunately, I sold that flexplate last year and don't have another one. You could very well be right with the heavier flywheel exaggerating a vibration that's always been there.

Daniel

You mentioned using a PRW flywheel, which one did you end up using?
https://store.prw-usa.com/products/f...eatured&page=1

I used their part number 1640081. I've spoken at length with Shaun, one of the tech's at PRW, and he confirmed early on that the actual flywheel I received is correct for my application.

Daniel

I could be wrong but this is my guess regarding the vibration. The flywheel you have is for a 1970-80 383/400 ci. in. stroker engine that's externally balanced, providing your internal crank is from the 400 engine with spacer bearings to acheive your stroker combo which I don't think you have. The 400's rods are smaller in center to center distance @ 5.565" & pistons have a 4.125" bore therefore the crank is balanced accordingly.
Your stroker could have aftermarket rods 5.7" or 6.0" with 4.000" bore pistons x 3.75" stoke as well.
Most stroker aftermarket 2 pce. rear seal cranks are internally balance but they do make an externally balanced one.

Here's an option before you dig into the internals. Get a flywheel & balancer that's internally balanced and see if it ails your vibration issue. I realize its quite a bit of work and you have to decide whether you want a billet flywheel and good balancer or the inexpensive stuff to try? I say get the cheap 150.00 stuff first to try it out. Down the road when you decide to balance the reciprocating assembly splurge then.

Engine update
 

I ended up pulling my engine in late May. Most summer events were cancelled and I didn't have any good reason to wait until this winter.

I decided to go with a local machine shop/engine builder to have another 383 built from the ground up. The new engine will have a roller cam/lifters, forged crank, forged pistons and will be internally balanced.

The builder sent me a few photos. Hopefully, assembly will start later this week.

Daniel

Did you seek an answer to the original problem so you would @ least put it to bed? Just curious if the machine shop noticed anything odd.

ScotI- This new engine is using a different, seasoned, block.

I sold the old 383 to a guy who was going to balance it with his flexplate and put it in a K5 Blazer with an automatic.

The final consensus was the old engine's rotating assembly was balanced with a flexplate when built and my "off the shelf" flywheel was "off" balance enough to cause the vibration.

Daniel

Got-cha. Seems very possible.

I could tell right away on my very first drive with my new 383 that the balance was MUCH improved. On mine, the crank with the flywheel was 15 grams out of balance and with the pressure plate bolted on was 38 grams out of balance.

Having it zero balanced with the pressure plate on made a VERY noticeable improvement, not only does it accelerate smoother but faster as well since it isn't fighting itself.

I had other people tell me before that it had a strange vibration feel to it but I never really noticed it. I just thought that was how 383s felt. Now I know.

Good luck with the new build.

Interesting & noted for future reference.

Hope this engine runs great for you, Daniel. I love my 383.

Getting closer
 

Slowly but surely...

Daniel

Now that's a sexy post!!

Engine porn... :thankyou:

Finally home...
 

Hopefully, my existing headers will work these angled plug heads.

Daniel

My current headers are 1 5/8” cheap Summit pieces. I’ve started looking around for a set of budget full length headers that work with angle plugs, but a lot of times it’s not specified in the listing.

Does anyone know of a set that definitely work with angle plugs?

Daniel

Is it just angled plugs you are concerned about or do those heads have raised exhaust ports as well?

My hooker 2466 were for stock height ports but we modified them to work with the raised port heads by elongating the mounting holes. They are "okay" with my angled plugs but you really have to be careful with gasket selection to make sure they seal up.

Lance- they’re not raised port heads. My current headers just lack the room on about 4 of the cylinders. I’ll be cooking boots constantly and may not even be able to get a spark plug boot on 1 plug. I may just bring out the BFH and massage them. I’m just not sure if I can gain enough clearance before trashing the headers.

Daniel

While I pretty much hate all headers on a street car, these Hookers are about as least hateful as I have been around. If you do decide to change and they fit your application, they are worth a look.

Thanks for the suggestion Lance.

I beat the crap out of my headers today and gained some decent clearance. The #3 runner needed the most by far. Hopefully, it’ll be enough to keep the plug boots from constantly melting.

I also measured the bellhousing runout and it came in less than 2 thousandths. So, should be good there.

Daniel

My brother and I got the engine/trans installed yesterday. I'll start bolting on the accessories soon and hope to start it up in a week or so.

Daniel

Nice!!

Similar issue on my 383 w/ Hedman mid-length headers and AFR heads, had to cut and grind a socket just to be able to remove one of the plugs. Even with fiberglass thermal sleeves around the boot had a couple melt. Also had access issues torquing a couple of the header bolts and found Remflex (https://www.summitracing.com/parts/rfl-2086) headers gaskets as the only way to stop exhaust leaks. PS: Looks super clean.

Engine start
 

Went to start the engine on Saturday and had to shim the starter a bit so the pinion would engage the flywheel. After that, it started on the first crank. :D

Oil pressure was good (about 65 psi cold), but I must've had an air pocket at the intake by the thermostat and water temp sender, because my fan didn't come on and I shut it down due to the temperature rising. There was also a coolant leak at the POS swivel water neck. I've tried vaseline on the O-ring, RTV, and flat sanding the mating surface, still leaks.

I ordered a different water neck that should be in today. Hope to get the timing, idle, and carb tuned and go for a drive soon.

Daniel

Good job! Glad to hear you're so close.

I always drill a 1/8" hole in thermostat flange to help bleed air out of system. Works like a champ.

Keep up the good work, cant wait to see how you like the first drive.

Thanks guys!

Lance- I did drill a 1/8" hole in the Stant t-stat when I installed the new water neck setup. Seem to do the trick.

I've noticed that with my water temp sender now in the head that my gauge reads about 15-20* higher than when the sender was in the intake. I haven't had any coolant spew out of the radiator, so I don't think the engine's actually too hot. Is that a common temp differential between head and intake placement?

Also, my timing was too advanced initially (fixed last night) and I believe my carb is too rich at this point. Both of which could possibly contribute to higher temp readings as well. I'm going to hook up my AFR gauge this evening and get that sorted.

Daniel

Just a data point- the water temp sensor in the head was actually reading about 20-30* higher than in the intake.

So, I decided to move that temp sensor to a port on the Vintage Air water neck riser I just got. Now the water temp gauge reads in a "normal" range.

Ready for the first drive this weekend. :)

Daniel

Good deal!! Nothing like that first drive...

First drive with new engine
 

Replaced the crap water neck I had, tightened up some coolant clamps, adjusted the carb and went for a first drive yesterday.

Smoooooooooth...amazing how smooth an engine is when balanced within a gram. :D

Daniel

It's crazy isn't it! Congrats...

Glad to hear there are no vibration issues. How's the power band?

Thanks guys. I've only done a short drive mainly checking for leaks.

We set it up for low end torque better suited for autocross. Using a dual plane (Performer RPM) intake and Comp Cam XR282HR.

https://www.compcams.com/xr282hr

Next drive I plan to lean on it and see how it does. :)

Daniel