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New 350/357 #19367084 vibrates at 1900rpm? Couple question.
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Post New 350/357 #19367084 vibrates at 1900rpm? Couple question. 
Just installed the engine in the wife's 70 Monte and have a couple lssues to figure out. I was looking for a GM crate engine forum to see what I could find out and stumbled onto this one.

1. 1st and most important is the vibration that hits at 1900 rpm and starts to smooth out a little as the rpms increase? This vibration is kind of like a harmonic vibration and is there whether the engine is under load or in neutral. It's seems to get worse as the engine heats up.

2. There is nowhere to mount the 1/2 npt water temp sender for the original gauge. All the ports on the vortec heads and the GM intake are 3/8 npt and there are no senders, that I have been able to find, that will fit 3/8 and have the correct values to work with the original gauge? The best solution I have been able to come up with is a spacer that goes between the thermostat/housing and the intake that has a 1/2 npt port. See any problems with this plan?

3. Thinking about installing a different converter. Car has 2.73 rear and will see no time at the track. Just looking for some thoughts on this?

Thanks,

S



Last edited by spoony on Fri Sep 15, 2017 5:25 pm; edited 1 time in total
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Do you have the correct balancer installed?
You can install the temperature sensor in the intake
Also congratulations you found the best and most knowledgeable gm form on the planet! Lol

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Bushwacker wrote:
Do you have the correct balancer installed?
You can install the temperature sensor in the intake
Also congratulations you found the best and most knowledgeable gm form on the planet! Lol


This was a turnkey engine that had the balancer pre-installed but it does feel something like a balancer that was incorrectly installed?

The intake ports are all 3/8 npt none are 1/2 or that would work. There are no 1/2 npt ports available that's why I was wondering about placing a spacer that has a 1/2 npt port between the thermostat and intake?

Thanks for the reply and welcome,

S

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I don't see a problem with installing the temp sender in a spacer under the thermostat housing. The other option is to have a machinist turn down the sending unit and thread it to 3/8 NPT. There was a guy over on the 67-72chevytrucks.com forum that was doing that for people. I would have to check and see if I can find him.

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Might check the flexplate. The website I looked at for that part number shows that it is supposed to have a 12.750" externally balanced 153-tooth automatic transmission flexplate. You'd need to check for cracks, and to make sure the weight is on there. If you installed the one off your old engine, this might be the problem.

Remove the accessory belts and run the engine up. Since it happens in neutral at 1900RPM, you can pretty quickly rule out the accessories this way so there's no need to worry about damaging the engine due to no water pump drive. No idea if you converted to a serpentine belt or not, if not this job might take a couple of hours but the multi-belt system will also let you check on a per-accessory basis instead of clearing all at once, and then having to figure out which one is bad.

Finally, what kind of fan do you have? A bad hydraulic fan clutch can set up vibration, and heat has a direct effect on this particular piece. This is another easy one to check, simply remove the fan and run it up. You'll want to make sure to re-bolt the water pump pulley before starting the car.

Perhaps this water neck might work?
https://www.summitracing.com/parts/spe-4730/overview/year/1970/make/chevrolet/model/monte-carlo

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Captainfab wrote:
I don't see a problem with installing the temp sender in a spacer under the thermostat housing. The other option is to have a machinist turn down the sending unit and thread it to 3/8 NPT. There was a guy over on the 67-72chevytrucks.com forum that was doing that for people. I would have to check and see if I can find him.


I was quite surprised how little information I could find on this. I figured there would be something on the Chevelle, El Camino, Monte forums but when I posed the question about this I didn't really get much. The vortec heads have the 3/8 ports but I think most people had intakes with 1/2 so it wasn't a problem for them.

The intake that came with this/my crate engine only came with 3/8 ports. I am not sure if that is a new development with GMs intakes?

Good to know I can install the spacer.

Thanks for the help,

S

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Speeder wrote:
Might check the flexplate. The website I looked at for that part number shows that it is supposed to have a 12.750" externally balanced 153-tooth automatic transmission flexplate. You'd need to check for cracks, and to make sure the weight is on there. If you installed the one off your old engine, this might be the problem.

Remove the accessory belts and run the engine up. Since it happens in neutral at 1900RPM, you can pretty quickly rule out the accessories this way so there's no need to worry about damaging the engine due to no water pump drive. No idea if you converted to a serpentine belt or not, if not this job might take a couple of hours but the multi-belt system will also let you check on a per-accessory basis instead of clearing all at once, and then having to figure out which one is bad.

Finally, what kind of fan do you have? A bad hydraulic fan clutch can set up vibration, and heat has a direct effect on this particular piece. This is another easy one to check, simply remove the fan and run it up. You'll want to make sure to re-bolt the water pump pulley before starting the car.

Perhaps this water neck might work?
https://www.summitracing.com/parts/spe-4730/overview/year/1970/make/chevrolet/model/monte-carlo


Just realized I had the wrong part number posted in the, edited, title. The actual number is 19367084. What I installed was the complete turnkey engine which had a new flexplate installed at the factory.

http://www.chevrolet.com/performance/crate-engines/sp350-357-turn-key

This engine came with a serpentine setup and all the accessories. I will remove, great idea, the belt and see what happens.

The one thing the new engine did not come with was a fan or fan clutch. It actually required, because of the way the serpentine belt is routed, a reverse clutch and fan which I purchased and installed. I have had fans cause vibrations in the past so I'll be looking at that as well.

I really appreciate all the responses,

S

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For your temp sender just go to Napa and buy a brass bushing 3/8npt to 1/2npt

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Removed the belt, plugged all vacuum lines, carefully went over entire engine checking for vacuum leaks, checked timing again and still have vibration issue? What am I missing?

This was a complete turnkey engine that came with a Holley 4150 that is supposed to be tuned to match the 350/357 specs. When I called Holley, trying to see if maybe there was something in the carb that should be looked at, the tech made the following statements.

I asked him about these engines/carb combos being advertised to run correctly when properly installed?
He said every car had its unique issues and might take a little tuning. I agreed with this in regards to weight, gear ratio etc. and while the car is being driven.

I mentioned my problem with this vibration occurs while in neutral as well as in drive.
He said I needed a bigger squiter?
How would a bigger squiter effect my engine above 1500?

Anyone know a good dyno shop, that is set up to work with Holley carbs, in Oregon?

It's too bad but I can't drive the car until I figure this out:(

Thanks for the help,

S

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Take the converter bolts out and slide the converter back and crank it and see if it vibrates you want be able to put it in gear but if the vibration is gone in neutral then you know it's the converter or pump

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