Strange unidentified knock from engine

[C5 Dude]

Originally Posted by grumpyvette

AirbornSilva where are you located?
If your local to west palm bch fla. I can help?
a logical set of tests should help,isolate the cause quickly, read the linked info below
that sound would make me do a compression test , you may have detonation damage on a piston, if the compression test shows all the cylinders are within about 7%-10% then Id suspect a burnt rocker and then readjust all the valves as the engines idling as a first test.
The sound sounds like a defective rocker , or busted valve spring, to me, you should be able to pull the valve covers one at a time and place your thumb firmly on each rocker applying pressure while the engine idles, if the rockers defective or valve springs busted, youll both hear and feel it binding and the sound will change as you apply some pressure.
once you locate the defective rocker (OR ROCKERS) or busted valve spring,youll want to replace them.


http://forum.grumpysperformance.com/...ng+down#p26074

http://forum.grumpysperformance.com/...ng+down#p19552

http://forum.grumpysperformance.com/...+spring#p26282

That is very true. I was going to mention this but alot of folks don't like the idea of running the engine with the valve covers off. It can be messy but it does help determin the problem lifter. I usually find it is the lifter and not the rocker but altho I havn't seen a defective rocker, I know others who have and know from them that it does happen. Heck, in all the years that I have been working on engines, I have found that anything that can hapen will happen.

[AirbornSilva]

Hi guys, sorry I must have missed my e-mail for the update on this yesterday.

Anyway, I decided instead of screwing around with the numbers matching engine I would just get a crate motor and put the other aside. I bought a motor from jegs, not much on the ponies side but I can deal with that later.

grumpy, I live in San Antonio Tx, wish I was closer from what I've read you certainly know your stuff. Maybe when I 'm ready to put a cam, heads and intake on this I'll pick your brain, that is if you don't mind

Thanks Guys!

[AirbornSilva]

Here's the specs on the motor I got:

This universal 350ci engine uses a brand new block and can be used as a replacement for most GM vehicles from 1973-85. It produces 260 HP and 350 ft/lbs torque with a 4-bbl carb and headers. It can be used as a replacement or as a retrofit into almost any vehicle. This brand new 350 crate engine comes with a GM warranty and is covered for 3 years or 100,000 miles in applicable GM vehicles only. JEGS has the GM Goodwrench, Chevy 350 engine for sale at a great price!
Specifications
· 4-bolt main with 2-piece rear main seal
· Cast iron crankshaft
· LT1/LT4 powdered metal connecting rods
· Cast pistons (dished)
· Hydraulic flat tappet cam (.383''/.401'' and 112° lobe separation)
· Cast iron cylinder heads with 76cc chambers
· 8.5:1 compression ratio
· Block is compatible with left or right side oil dipstick (Requires Plug for Unused Side - Plugs are Included)
· 4-quart oil pan
· Timing tabs for a 6-3/4'' or an 8'' balancer
· Recommended spark plug: Accel #111-0574-4 or any spark plug with 14mm .460'' reach, 5/8'' hex, tapered seat, projected tip

[grumpyvette]

Ive installed several of those 350 cid /260 hp crate engines, for guys replacing busted early c4 corvettes engines ,who were on small budgets.


Id suggest you read thru these links below.
you can make several mods that will boost hp without investing a great deal more time or money


http://www.rustpuppy.org/chp/

http://forum.grumpysperformance.com/...php?f=69&t=519

[AirbornSilva]

Thank you Grumpy, I'll check out the links for sure

[AirbornSilva]

Those are some good articles Grumpy (but then you knew that), they are getting right about my target of 400 HP out of essentially the same crate motor I have, encouraging how little they did to get there too