[wakesupremo]

Hi all. I have a late 400 block that only has the bosses for motor mounts in 1 position. I have a friend that would like it for his '65 Le Mans. What would be necessary to make it fit? Thank you in advance.

[400 Lemans]

https://www.motortrend.com/how-to/ea...ount-adapters/

[ZeGermanHam]

Most Pontiac blocks from 1970 onward have 4-5 engine mount bolt holes in each side so they will fit any chassis. When was your block made?

[Sirrotica]

The last year was 76 for the dual fit 5 hole blocks. in 1977 both the 400, and 301, and later on (80-81), the 265 had only the later style 3 hole mounts.

I ran into the motor mount back in 1977, trying to put a 69 428 into a 73 Firebird chassis, and made up the strap mounts before anyone offered them for sale. One thing to be aware of, the adapters won't be as strong as bolting the mounts to the block, if you beat on the car, they will twist from the stress. I've seen two sets twisted on cars that were abused.

If you want to use the adapters, I would also restrain the engine with a restraint connected from the left cylinder head, and the left frame rail. That extra restraint will keep your adapters from deforming, or the motor mounts from breaking. I use a 3/8 inch turn buckle to limit the movement, plenty strong enough, and adjustable to limit the movement of the engine. this also takes twist load off of the cast iron area above the oil pan rail, as you will only be using 2 bolts, instead of the later 3 hole design.

Hopefully this is adequate information to get your late engine in an early chassis.

[77 TRASHCAN]

Can the bosses be drilled and tapped, to use the early mounts?

[Sirrotica]

Originally Posted by 77 TRASHCAN

Can the bosses be drilled and tapped, to use the early mounts?

Although some of the late blocks had the bosses, most didn't have them. Usually there aren't any there, they were eliminated from the mold patterns.

I have seen maybe a couple late blocks where the metal was still cast, and could be drilled and tapped, but for the most part, there is no cast metal there.

I believe some early 77 blocks still had the metal there, but soon after it was eliminated. Just my thoughts. I don't have any documentation to substantiate that, but most of the late 3 bolt blocks only have 3 bosses, not 5. don't forget, 77 was the year GM started cutting any metal they could from the engine to try to meet CAFE standards.

I still remember the first time I pulled the timing cover off of a 301, and noticed the timing chain was thinner. they cut 2 rows of links off of the timing chain to reduce weight.....

Lost the counterweights on the 301 crank, and trimmed the balancer to almost nothing. they also cut huge triangular slots in the flex plate instead of the previous 6 holed flex plate. The 77 flex plates cracked very easily with only 3 spokes holding the ring gear to the crank. The changes were just a few grams here and there, hardly enough to make a difference in fuel mileage, but enough to cause reliability problems, along with cutting the nickel content in the block made them less wear resistant.

Then they took so much metal out of the block, the main bulkheads, and caps were prone to cracking. The famous 557 lightweight block was costing them warranty money, so they brought back the old casting in 78. Come to think of it, the heavier duty 78-79 block may be the ones with the 5 bosses cast in, with only 3 tapped....

[Scarebird]

It may be easier to use the later clamshells in the 65 chassis?

Bolt up the mounts and clams, lower engine into position then mark on frame where to drill. Remove, drill, mount clams and reassemble.

If this does work you will have the far superior clam mounting setup.

[Sirrotica]

The problem with that is finding the 3 hole block brackets is sometimes less than easy, There may be some 3 hole brackets being made aftermarket, seems to me Butler offered some for an F body.

Link to Butler adapters for engine mounting adapters:

https://butlerperformance.com/c-1393...-adaptors.html

There are also 3 different sets of frame brackets, for full size B body, a set for A (73 and later) and F body, then I believe the G body (301) needed a set because they're a much narrower frame from rail to rail.

Also the 65 A body crossmember isn't as massive as the later model frames, and being that Pontiac moved the mount system forward about 4-6 inches, the mounts may have nothing under them. If you're going to attempt doing this on an 65 A body, you'd be in uncharted gray area.

Using the adapter plates at least matches the positioning front to rear to the chassis the engine is going into.

After giving it some thought, the 3 hole mount was used on all 455 A body cars from 70-72. Another way to do this with factory parts would to use 70-72 455 A body mounts, and then come up with the frame mounts for the same car. No they're not clamshell mounts, but that setup was at least employed on the later chassis. There is no guarantee that it would fit a 65 chassis as the engine position was moved rearward in 68, but it would be far more likely than using a set of F body mounts would.

Again finding used parts to make the swap is going to be a problem because there weren't a ton of 455 equipped A bodies made from 70-72. Finding used parts is going to be the stumbling block. Then you may still have the mounts hanging in mid air on the 65 chassis because of the engine setback from 67 to 68 on A bodies.

Either option is going to be try and see if it fits, but you'll have to come up with the stock factory parts before you even know if it can be made to work.

[wakesupremo]

Thanks all for the replys. I really don't know the actual year of the block but, I know that when I fitted it to my '69 firebird i had to make adapter plates to bring the mounts to the correct location. The person that is interested in buying this from me now would like to know if the same brackets will allow it to fit his 65 le mans.

[25stevem]

If I am not mistaken all of the 1979 motors where cast in 78 making the block having the 5 motor mount pads or not a hit or miss deal.

[67Fbird]

not sure what teh A-body mounts are like but I had to go the OTHER direction 100 yrs ago with my 2nd gen F body,,,usiing a 1967 400 only having 4 pads and 2 tapped holes, needing exactly what WASN'T there....lol

[Sirrotica]

As long as it's a 3 bolt block (77-79), and your mounts fit the 2 bolt motor mounts they should work fine. That's the only 1 of 2 possibilities late block to early frame, or early block to late frame.

The adapters are just reversed, depending which way you have to adapt the mounts to block. The holes are in the same places, the usage changes depending which way you're needing to go.

After 76 the 5 holes went away, some blocks were cast with the bosses there, but they were never drilled and tapped for the 2 hole mounts. Most times the bosses weren't even there. Finding a 77 and later block with the bosses for the 5 hole pattern would be like winning the lottery, most unlikely.

As with most times with Pontiac, there were a few here and there that slip through, I've learned never say never when it comes to Pontiac exceptions, but if you're a betting man, you'd likely win the bet.

[Sirrotica]

Originally Posted by wakesupremo

Thanks all for the replys. I really don't know the actual year of the block but, I know that when I fitted it to my '69 firebird i had to make adapter plates to bring the mounts to the correct location. The person that is interested in buying this from me now would like to know if the same brackets will allow it to fit his 65 le mans.

If you don't know the year of the block, it's usually cast right next to the distributor hole in 2 digits, such as 70, 72, 77, 78 etc.

Holes are in the same place on the adapters, just which way the bolts go in changes depending upon usage (early to late, or late to early).

[Chris65LeMans]

I have a ‘65 LeMans, and my previous Engine was out of a 69 Firebird.

[77 TRASHCAN]

Did you finally get the new engine, in your car and running?

[Chris65LeMans]

Originally Posted by 77 TRASHCAN

Did you finally get the new engine, in your car and running?

I did. It’s been up and running for a few weeks. Took the kids for a nice, long cruise today. There’s so much power that I don’t dare use it all.

[wakesupremo]

Thanks for all the replys. Unfortunately the person has decided to pull out of the sale as he wants a direct bolt in engine!!!!