421 SD in a 65 GTO? - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 04-16-2016, 03:15 PM Thread Starter
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421 SD in a 65 GTO?

I recently purchased a 1963 421 sd engine and had it rebuilt. I am ready to install it in my 1965 GTO and I am being told that it won't work because of the starter and bell housing? I planned on hooking it up to the factory 4 speed manual trans that came in the car. Is this true? Can it be done? if so what do I need to do and how hard is it going to be?
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post #2 of 4 (permalink) Old 04-16-2016, 11:41 PM
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From one of the books I have on building Pontiacs, it states that you will have to use the starter/bellhousing that fits your '63 engine and you will also have to use an early model transmission. Check this out: 1961 - 1968 Pontiac Bellhousing Identification at Pontiac Paradise

However, I did find this adapter that uses a Mopar starter and will adapt early Pontiacs to a Chevy or BOP automatic. Wilcap Pontiac Engine Adapter Page I am thinking that this adapter should also allow you to mount the later Pontiac bellhousing and the Muncie 4-speed. The only problem I see is that the adapter will locate the bell back whatever the adapter thickness is. It could effect how deep the pilot shaft on the transmission goes into the pilot bearing(which may not be a problem) and it will change the geometry on the clutch fork which will need to be compensated for with an adjustable clutch fork ball that goes on the bellhousing or even a custom made one that will get your clutch fork at the correct angle needed to operate the clutch.

In my youth I mounted a built 409CI Chevy into my '67 GTO convert. using Chevelle frame mounts, and a trans adapter to bolt on the Pontiac bell and the HD Pontiac 3-speed manual trans. It was a screamer, but I could never get a clean shift out of it no matter how much adjusting I did to the linkage. What I failed to understand was that the adapter moved the bell/trans back and I did not know that I had to extend the clutch fork ball with one of the adjustable/longer aftermarket ones to get my geometry back. Got frustrated and parked the car and eventually sold the body minus the engine. If I had known what I know today, .......

So do a little checking around on the internet and email a few of these guys who make adapters and it it may work for you.
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post #3 of 4 (permalink) Old 04-18-2016, 08:38 PM
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A real 1963 421 SD engine had an upside down starter nose in order for the starter to clear the '63 long branch exhaust manifolds and the Catalina chassis. Nunzi in the late '70's had a few and offered the unique starter nose hsg in his catelogue...a very rare part.

'63 421 SD engines usually carrried the "980" casting early SD heads. These had a wider spread between the center exhaust port exhaust manifold bolts. Wider than previous '61-63 cylinder heads, wider than the more civilian use '63 and '64 cyl heads. If you do have have an original '63 421 SD engine, it's a very valuable piece. The "980" casting heads will only mate up to the correct '63 long breach SD manifolds, or the correct '63 Tempest factory tubed ex "manifolds". Installing a '63 421 SD into a '64 or later Pontiac LeMans or GTO would require several things.

- Buy a set of custom headers for the installation. 45+ years ago old school header mfg'ers like Jardine made headers for drag race installations of the '63 SD headed engines. Today, one might be able to find a set, and have them repaired, otherwise, it will be custom built headers, expect a bill of at least $1200.

-the '63 block, like all '63 and earlier Pontiac blocks is not going to have the "ear" to bolt on a starter. On a street car or a street/strip car one can get by using a '62, 63, or '64 cast iron bellhousing from a Catalina, Starchief, or Bonneville. These are very tough to find, I've had 4 of the cast iron bellhousings from those years. One, 15 years ago went on '62 389 that went into a '64 GTO clone convert. On that mess, the owner bought for $75, the wrong 389 block core off the local yokel '65 GTO clone car guy ( felliw lived at local yokel car shows). The buyer had noone knowledgeable for guidance, and had all the machine work and assembly done on the '62 389 and gad it topped off with a shipped in $2000 '64 tripower. Then he paid a pair of local European sports car guys to install the engine and Muncie at their restoration shop. These two got the engine and transmission in the LeMans convert and couldn't figure out where to bolt the starter on! Through some dialing around, they found out the early Pontiac V8's had a starter that mounted to the bellhousing. Local mini starter manufacturer, GPE, was called, and their machinist called me. Correct cast iron bell hsg and custom (early) Pontiac mini starter ended up running the clown car car builder little over $650.

-Another solution is use a custom midplate on the back of the block and mount the starter to it. have examined this setup before on racecar builds with the early blocks ( typically '59 389 blocks, as they are thick and can be bored out .090, sometimes, .120)

-last solution. in the early 90's, I picked up a '63 421 mid horse application block. Someone, very skilled, had taken the starter ear off a later block, machined it and the rear corner of the block, then took the block to a shop that furnace welded the cast iron starter ear onto the '63 421 block. I was very impressed by the work at the time, would have hated to have had to have paid for the fitting and welding.

Hope this helps. Love to see some pics of the engine. Which intake and carburetion came on the SD engine?
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post #4 of 4 (permalink) Old 04-18-2016, 09:00 PM
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I put a '63 421 into a '65 Convert. That was a few decades ago and I still remember crawling under the car with the starter and discovering that there was no place to bolt it.

I ended up making a midplate to install between the engine and bellhousing. The Midplate had provision for the early starter. I then had to turn the starter nose off in the lathe, rotate it until the solenoid cleared everything and then I brazed it back together.

If you modify the starter be sure that the starter rotor lines up with the bushings and put a stop on the shaft to keep the Bendix drive from hitting the now slightly shorter starter nose.

I had a lot of problems with the clutch linkage but I think that was due to having a pile of modified Chevy parts more than anything else.

After getting everything sorted out over a couple of years I drove the car fro many enjoyable miles.
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