1963 340 HP Rebuild

[Ray C.]

I am currently restoring a 1963 340HP SWC. I needed to remove the body because the frame has some rust and needs repair. The car seemed very original and unmolested when purchased. I currently have the body off and started to disassemble the engine for evaluation. I believe that this engine has never been apart or rebuilt. It has the original GM main bearings, 098 cam and what I believe to be the original head gaskets. The front and rear intake gaskets are extremely brittle. The thermostat housing is the correct 3827370 casting number, but was painted orange not silver. I steeled brushed part of the housing and found no signs of silver paint. If anyone is in need of any information on an un-restored 340HP now is the time to ask!

Ray #36314

[Michael H.]

Re: 1963 340 HP Rebuild

Ray,

One head gasket per side, or two? Are the "Job Number" and "Suffix" (RE)characters visible on the end of either cyl head? Is the engine suffix visible on the lower portion of the block, just above the coolant drain plugs? Thanks.

The thermo housing would have originally been painted with a light coat of silver that most likely went away many years ago. I suspect that some previous owner painted it orange.

[Ray C.]

Re: 1963 340 HP Rebuild

Hi! Michael

The cylinder heads were double gasket on both heads. I cleaned the block above the drain plugs on both sides and found no letters or symbols, but there seemed to be a silver/blue paint dabs on the front and rear of the left side and one paint dab on the right rear. The orange paint coverage in these areas was marginal at best. The right cylinder head had crayon marking of 464 on it and the left had no markings.

[Michael H.]

Re: 1963 340 HP Rebuild

Thanks Ray. The number on the cyl head looks well preserved. It should match the "job number" that's also hand written on the body just below your heater assy. The engine code that was on the lower sides of the block would have been written before the orange paint was applied so you may not see that until after the paint is removed. Nice to see all the original markings.

[Joe L.]

Re: 1963 340 HP Rebuild

Ray----

Can you confirm the type of camshaft timing sprocket the engine has? It will be either aluminum with nylon teeth or cast iron. I believe that it should be iron, though. Also, what GM casting number is found on it?

[Duke W.]

Re: 1963 340 HP Rebuild

'63 vintage should be iron. The junky aluminum/nylon sprockets didn't go into production until about 1968.

Duke

[Ray C.]

Re: 1963 340 HP Rebuild

Hi! Joe

Iron with the following on the sprocket

GM 32

#3704214

Ray

[Ray C.]

Re: 1963 340 HP Rebuild

Hi! Duke

Just reading an article on PT differentials in the Restorer. Could you please answer a couple of questions: I am in need of a differential cover for the 63; it currently has a service replacement. I believe that 63 through early 65 are the same. Were there any dates or other indicators that would suggest the actual year? The rear leaf spring seems not to be the original, but never seeing a 63 spring it is hard for me to confirm. The current spring has a raised section or bump at the end of some leaves, and a short spring liner is inserted into. The spring shows age and rust so it is defiantly not a recent replacement. The ends of the spring do not curl up and they all are arched.

Thanks for any help!
Ray

[Duke W.]

Re: 1963 340 HP Rebuild

Joe is better positioned to speak to the external configuration of the axle covers. I believe most are interchangeable from '63 to '79, but Bill and I only dealt with the internal mechanicals of the axle, which are mostly the same except for the spline count on the '63-'64 drive pinions and the companion flange designed for a larger U-joint in the seventies.

The '63 base suspension leaf spring is a constant rate design, which means all the leaves have the same arch. Beginning in '64 the base suspension rear leaf spring is variable rate, and these are easy to identify with no load on the spring (or just by jacking up the rear end) as some leaves are essentially straight with no arch.

The main (bottom) leaf on my original base supension '63 rear spring is flat with no "upturn" on the ends, however ALL other leaves have upturned ends, so if I am reading your post correctly, it sounds like you have the original '63 rear spring. Since they are unique to the one year they are fairly easy to identify.
Over the years there appear to be subtle changes in the geometry of the main leaf ends (repros too), but I can't remember all the details off the top of my head, though they have been discussed in Board threads and articles in The Corvette Restorer.

BTW, regarding your engine, I hope you understand that the original connecting rods are best used as paperweights. These early small bearing 327 rods are weak. At least replace them with the later design small bearing rods that went into production in late '66 or early '67. For mechanical lifter engines I highly recommend Crower Sportsman rods. They are relatively expensive, but will virtually ensure a bulletproof bottom end as long as it never runs out of oil. I recommend OE or OE equivalent parts for the rest of the engine, so there is no need to waste money on "hot rod" parts. There are lots of threads on conn. rods including one in the last month or so, which covers most of the details.

If you want more top end power, investing in pocket porting, port matching, and multiangle valve seating will generally yield a good seven percent increase in top end power with the same cam. I also recommend the LT-1 cam over the Duntov cam. They both have about the same overlap, so their idle characteristics are about the same. The Duntov cam was designed for the old medium port small valve heads and it's a bit restrictive with the larger port 461 heads and longer stroke of the 327. I do not recommend increasing the valve sizes on 1.94"/1.50" heads to the 2.02"/1.6" sizes. Inlet flow could actually be worse unless the radius chamber cut centered on the inlet valve stem is accomplished as it was on OE heads with the larger valves. Even with this cut, the flow improvement is marginal, but the risk of a crack between the valves increases significantly.

Massaged heads and the LT-1 cam will yield about a 20 percent improvment in top end power, with about the same idle quality, low end torque, and peak mid-range torque as a production 327/340.

In production trim the 340 only produced, at best, an honest 300 HP gross at about 5500. (The 300 HP engine was actually about 250 true at 4500). With the LT-1 cam and well massaged heads, it will make about 350 SAE gross at 6500. This will yield about 315 net and about 265 at the rear wheels.

Only cut metal if absolutely necessary. Of course, you don't want to deck the RH side of the block, and I don't believe in cutting the head surface, either unless it is absolutely necessary. Using a machiniest bar and a .0015" feeler gauge, it's easy to determine if the surfaces are flat, which they probably still are unless the engine has been overheated. It's normal to assembly the engine with composition gasket and they will usually seal with up to about .003" warp.

Also be sure to measure deck to piston crown clearance for all eight BEFORE you disasseble the block. This will tell you if the decks are parallel to the crankshaft (They usually are.), and if the decks are equal height (The usually aren't) This also gives you the basic data you need to compute the compression ratio of the rebuild and you should target no more than 10.5:1 with the OE replacement forged/domed pistons, which will usually be the case since the OE deck height is usually .010"-.015" above the nominal 9.025" blueprint dimension.

If the left hand deck is high, it can be milled to equal the right side,,and you can also buy compostion gaskets of different thickness to equalize quench clearnace.

The crankshaft should be miced, checked for staightness, and preferably Magnaflux inspected. It is likely that the crank journals are still within original machining tolerance. Since the crankshaft has the Tufftride surface hardening turning it will remove this hardened surface and reduce crankshaft durability.

You have to be very careful with machine shops. They will often deck blocks, heads, and grind cranks "because we do them all that way". Be sure you only contract with a machine shop that understands "restoration" as apposed to "rebuild", and give them very specific instructions as to what work you want accomplished, and make clear to them that only that work is to be done. If they don't "get it", find another machine shop!

Duke

[Ray C.]

Re: 1963 340 HP Rebuild

Here is a picture of the rear spring:

[Duke W.]

Re: 1963 340 HP Rebuild

It's tough to tell from the photo, but if the main leaf does not have upturned ends and all the others do and all curve in about the same arch, it is probably original. It does not look significantly corroded and should be completely rebuildable with a clean up and new liners. Though as originally built they only had a thin layer of grey paint on the bottom side, I chose to paint each leaf completely, after cleanup and prior to assembly, with a good primer-top coat system to arrest the possibility of future corrosion. With no driving in the rain I figure is should last at least another 100 years.

Duke

[Ray C.]

Re: 1963 340 HP Rebuild

Thanks to all!

Ray