AirborneSilva

Maybe you said this but are you running iron or aluminum heads? Just curious

c3_dk

Iron, std. L46 1969 engine, nothing changed. (std. 186 2.02/1.6 heads, cam ec ec)

AirborneSilva

Ok thanks, I just installed aluminum heads that put me at 11:1 compression (according to Sumitt's calculator) and I've had no issues

c3_dk

I am glad you have no problems.
I am sure that alu heads helps ALOT, cooler engine "new" combustion chambers. I am sure this would help me also.

I also run with cool sparkplugs, 160 thermostat, and still on a hot day, I have problems.

AirBusPilot

Did the engine knocked since it was rebuilt?

AirborneSilva

Sorry brother, I hope you are able to get it figured out without spending too much money

Sweet70

I agree with the thought process re what's changed ... basically a lot.

I purchased the car about five years ago at that time it was mostly original but in need of a restoration. Since then I have restored or replaced just about everything that moves. I took the body off and kept going until there was an empty space. I don't recall having this problem prior to the restoration work. It did have an old holly carb that I replaced with a correct Rochester. The Rochester was completely professionally restored at the conclusion of the engine rebuild. Things that have changed on the engine are, the block bored, I think it was 35 over. Pistons and rings replaced to keep the 11:1 compression ratio. Crank polished, main bearings changed, valve seals and springs, oil pump, water pump, harmonic balancer, cam shaft, lifters, timing chain, fan thermostat, coolant thermostat changed to 180, hoses, belts, replaced. On the distributor I replaced the vac can to a B28 due to low manifold vacuum at idle. I have replaced the points with a Petronics Ignitor III (71181) and a matching high performance coil, Ignitor 111 (44011). The idea here was to retain an original look and do away with the issues of points, dwell etc. My plugs are new within 500 miles AC Delco R43. I increased the recommended gap from 35 to 40 to allow for the higher output coil. At the time of installing the Petronics system I adjusted the distributor drive gear with a shim back into spec. I visually checked the distributor drive
shaft along with the lower and upper bushings for wear. I changed the cap and rotor within the last 500 miles. My issues were apparent prior to the Petronic changes. I had problems with running after the engine rebuild.The engine would not idle below 1000 rpm, through the "forum" I was introduced to Lars vac can selection and timing papers. This has been very helpful as I believe my vac can was bad and switching to the B28 has been a tremendous help. Now my engine starts, idles and generally runs well, if I could eliminate the knock in 1st & 2nd ... I'm done. I don't want a hot rod nor a race car, I want a hobby car that's fun to drive ... shoot, it's not even a good investment!

If you have any suggestions please feel free, I'm going to try a couple of the current suggestions tomorrow then disconnect the battery, put the cover on and head off up north in the cool for a few weeks.

Thanks for your time.

Mike Ward

I'd start with real basics. Engines can make all sorts of rattly sounds not associated with detonation.

Put a real strong rubber band around the weights to keep them from moving and go for a drive. Disconnect and plug the vacuum advance also.

AirBusPilot

Put 10 gallons of 110 octane race fuel in it and see if it still knocks.

Sweet70

Sounds like a novice question but where can you typically buy race fuel?

AirBusPilot

Varies by location, but try a local speed shop. They at least would know. When I lived in Phoenix, there were a few gas stations that had it at the pump!

Sweet70

My thanks to all those who offered suggestions. I have a numbers matching L46, heads and inlet manifold are cast iron ... not sure what that aluminum head talk was about.
Based on the many suggestions here's what I plan to do as time permits.

Current … Est advance “all in” @ 36* black/silver springs 2650 rpm. Engine knock in 1st & 2nd gears under load when engine is hot.
Plan ‘A’ ...
Plug vac can and see if knock changes.
Rubber band centrifugal advance and check for effect.
Reset advance to stock at idle, 8* advance + 12* vacuum advance = 20* total @ 750 rpm. This is about 8* lower than current following timing/vac can papers.
Try stock and kit spring combinations in centrifugal advance.
Read spark plugs, try cooler range.
Plan ‘B’ …
Degree the cam
Better understand options to increase fuel flow from Q’Jet, carb replaced during engine rebuild.
Try a higher octane fuel … but it needs to be readily available.

Thanks for your time, any other thoughts, please feel free

Revi

Unless you decked the block during overhaul, you most likely do not have true 11.0:1 compression (static).
A stock GM block has around .020/.025 deck height. A Flint produced L-46 did not have a true 11.0:1 c/r when it left the factory.
Dependant on your deck height and head gasket thickness, you most likely have somewhere in the mid 10.0's:1 for compression, which should run fine on 93 oct.. Usually somewhere around 10.4/10.5:1 is the make or break point for 93 oct. fuel.

c3_dk

You are on the right track, you can also run 160 thermostat, to get a nice cool engine.

augiedoggy

Maybe they used shim head gaskets when rebuilding your engine which would have increased your compression?you should be able to get a feeler gauge between the head and block somewhere around the perimeter of the head and check its thickness...

Sweet70

Thanks but I fear my foot was out to be shot at! I wish this were the case but I fear not. The block was not decked when it was bored .030" over. But the replacement pistons were upped a bit to allow for this. The piston specs are,
Sealed power 8-KL2304F-30 - Speed Pro Power Forged
Compression ratio: 11.40 :1 with 58cc heads. 9:31 with 76cc heads. I think mine are the 58cc variety. I'm not sure about the head gasket used I'd need to check that but as far as I can recall I used an engine rebuild gasket kit from a major corvette catalog supplier. If there is a specific head gasket to be used please let me know. Changing the head gasket isn't a 5 minute job but I'm getting a feeling the engine is coming out again this winter.

AirborneSilva

From what I've been told aluminum heads allow you to run more compression before you experience knock with 93 octane fuel.

Sweet70

At the vin plate and head right side seems like .033" same on the left side. Thoughts?

REELAV8R

Those pistons have a 2.4cc dome. Combined with your 58 cc heads you got too much compression. Not only that but, a dome impedes flame front travel which would make the situation worse.

If you used a .035 (?) thick head gasket and did not shave the block down any then stock deck height is 9.025". this would put the piston (squish band anyhow) .025" down the hole. .035 + .025 = .060" for your squish band. This would be a detonation prone distance even without 11.4:1 CR.
Combined, I don't hold much hope for loosing the detonation without changing either the heads or the pistons and then put on a .015" head gasket.
I'll keep my fingers crossed for you though.

c3_dk

Are you saying my 69 L46 pistons is 2.4cc??
If yes, then I don't have to measure them.