Just started 350/290hp crate motor have ?'s

[Greubin]

UPDATE: The stumbling turned out to be a defective HEI distributor. Replaced distributor and engine now runs fine..BUT - unfortunately the engine has developed a knock at idle up to 1500 rpm. I've probed the engine with a stethoscope and these are a list of the things I know are not related to the knocking sound.
-valve lash adjustment
-fuel pump
-flexplate
-transmission
-alternator and power steering pump


The sound is loudest near the top of the bell housing, which I thought would be a cracked flexplate - but that's not it - I went so far as to replace the flexplate just for good measure. Listening with a stethoscope, the bottom end sounds, rocker covers and accessories sound tight. It must be related to either a main or rod bearing..but not sure. For warranty work, I have to take it to a GM dealer for evaluation, but I hate to think what they'll charge me for a diagnostic.


Any suggestions?

Previously -
Started up fine, did the 2000 / 20min break-in. Have one problem, the engine won't idle below about 1500rpm. I installed an HEI distributor, but I'm running the same plugs off my old engine, as they have about 1000mi on them( regapped to .045" for HEI ). The engine surges below 1500 rpm, and takes some foot work to keep it running at 1000-1500rpm. At 2000rpm, it runs steady.

Any ideas? I'm gonna double check the plugs and make sure they're the correct plug for HEI.

The other thing is the oil pres. seems high during the break-in - it was just below the H mark on the pressure gauge, even after engine was up to operating temperature.

Everything else looks okay, and no leaks.

[rage'nrat638]

sounds like a carb problem to me.
i would think the plugs are fine. what kind of carb you got?

more than likely you have a high volume oil pump. if your running a stock oil pressure gauge, your going to want to look for a HD truck oil pressure gauge that reads upto 80 psi
MARK

[Greubin]

Originally Posted by rage'nrat638

sounds like a carb problem to me.
i would think the plugs are fine. what kind of carb you got?

more than likely you have a high volume oil pump. if your running a stock oil pressure gauge, your going to want to look for a HD truck oil pressure gauge that reads upto 80 psi
MARK

Edelbrock 600 ( 1406? ) Ran fine on the old engine, maybe i have a vacuum leak that I don't see.

[rage'nrat638]

o yea is the carb new or old..no vacuum leaks right ?

yup spray some carb cleaner around the base of the carb and vacuum fittings and see if you notice a rpm change..if you do you have a vacuum leak...

[Greubin]

Originally Posted by rage'nrat638

o yea is the carb new or old..no vacuum leaks right ?

yup spray some carb cleaner around the base of the carb and vacuum fittings and see if you notice a rpm change..if you do you have a vacuum leak...

It's about 3 mos. old.

[Greubin]

update TTT

[VetteVet]

Am I to understand that the new HEI dizzy fixed the idle problem but you now have a knock and it goes away after 1500 rpm?
I don't think it's a rod because they don't go away. You could ground one sparkplug wire at a time and see if it makes a difference. If it's a rod bearing the piston not firing takes the load off the bearing and the sound gets quieter.
The location you hear it at, leads me to the torque converter.
If I were worried about the high oil pressure I would get an aftermarket gauge and install it. After a few thousand miles the pressure will drop and you will be able to read it on the stock gauge.

[1970 CST Short Wide]

We have one of these motors in my sons truck. It started useing oil , ~4 qts in 2000 miles. It turned out a couple of the guides were bad. The shop that fixed it said the guides were to long and were hitting the retainer which ruined the seals, could this be your noise????

[glock35ipsc]

I put one of those motors in my 70 K10 several years ago. It developed a "knock" kind of like you describe. Mine turned out to be a leaky manifold-to-head gasket on the #7 cylinder.

Honestly, it did not sound like an exhaust leak. It sounded like a broken weld on the flexplate, or a loose rocker. But strangely enough, it went away with RPM. Once I found it (by accident, felt the puff-puff-puff that went with the noise while poking around) and replaced the gaskets, no more noise.

[motocrosschump]

You can disconnect the tranny and start it and see if the problem goes away.

[MisterMan]

possibe intake leak, did you use the lil cork seals on the intake??? pop your oil filler cap and listen, if that bad of a leak, the oil filler will be like a vaccume.

EDIT: also, yes, check thoes plugs, you may have to run thoes irdum (sp) bs things

[Greubin]

Originally Posted by motocrosschump

You can disconnect the tranny and start it and see if the problem goes away.

Yup, I disconnected the torque converter and still have the sound. I'll check the manifolds for exhaust leaks.

[Greubin]

Originally Posted by 1970 CST Short Wide

We have one of these motors in my sons truck. It started useing oil , ~4 qts in 2000 miles. It turned out a couple of the guides were bad. The shop that fixed it said the guides were to long and were hitting the retainer which ruined the seals, could this be your noise????

Interesting - I noticed I have a little bit of smoke coming out of the exhaust, but thought it would be normal for a new engine to do that during the break in period. I checked the rocker covers for noise, seemed farily quiet, I could hear the valve train working, but nothing abnormal.

I stopped by the local machine shop for another project and had the mech listen to my noisy engine. He seemed to think it was piston slap, and said the crate engines normally run "a little loose" and are noisy. Dunno - jusry is still out on this...

Thanks for the replies.