Motor mount adapters - ‘69 428 in ‘70 Trans Am
 

As some of you know, I have an ongoing thread in the Street forum where I’ve decided to build 4.00” stroker engine using my original WS 400 block in my ‘70 TA. The biggest delay in the supply chain will be getting the pistons, but I need to pull the 400 out in order to determine if it will just need a clean-up hone, which I suspect because the engine only has ~6000 miles on it since it was rebuilt by PO, or if it will need a re-bore.

I’d like to still drive the car while waiting for the parts and I do have a good 428 (670 heads) combo I can run until the 400 is done. I had another thread about maybe updating the 428 with different cam/heads, but I think I would just drop it in ‘as is’ for now.

My question has to do with the adapters used to fit the earlier blocks that only have 2 motor mount holes into a 2nd Gen car. I see that Ames has an adapter that appears to be a piece of flat stock with extra holes drilled in it for $62. Butler has something similar for $59, but also has several other options that range from $115 to $300 (yikes). I also doubt another site called Firebird Central has them for $129.

Any recommendations?


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Not sure what's available today. Back when Nunzi and H-O Racing sold them you would have to exchange the frame brackets for the 75-81 mounts and they supplied you with a mount & bravket that looked like the mount set up for the Olds 403.

Changing the frame brackets to the later motor mounts is the main reason I sold most of my 428's back in the day.

The Ames pieces work fine, and use the 70 motor mounts.
Paul, these are just Engine side plates, not mounts at all.

Thanks FB. I’m going to order the Ames kit or from Butler - they have basically the same one that looks like flat stock.


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After a long back order, I finally got the adapter plates to put the 428 in the TA, while I rebuild the original motor (decided on going with a 4” stroker, but keeping g the factory #12 heads- Paul you’ll be getting a call shortly [emoji3])

Here are the brackets:
https://uploads.tapatalk-cdn.com/202...86325c866a.jpg

And here is the 428 that’s going in with the 670 heads (I don’t think I’ll be running the Holley Street Dominator, it’s just sitting on top)
https://uploads.tapatalk-cdn.com/202...4ff3d65164.jpg

A couple of engine pulling questions (it’s been a few years). Do you guys like to leave the trans (M21) attached when pulling the engine, or separate them?

Also, obviously the hood has to come off the TA, but would you also pull the radiator? What about the nose? My concern about pulling the Endurance bumper is that I don’t think I could ever get it aligned putting it back on.

Thanks!


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I personally find it exponentially easier to attach the transmission when the engine is out;
I prefer to install the engine with transmission.

My first foray into the mount adapters was the same engine swap, A 69, 428 into a 1973 Esprit, circa 1977. I made my own adapters from steel strap. I sold them for $20 a set back them, as it was the only game in town at the time.

I had a service station/garage in Erie PA, (Yost Pennzoil Service) that specialized in Pontiacs, especially high performance Pontiacs. In my third signature picture, you see the light brick building behind the 69 Grand Prix dirt car, and see the advertising on the front fender.

The word got out that if you had a Pontiac that didn't have the proper 5 bolt dual fit pattern block, that I had adapters that would allow you to make the swap. I kept usually 1 of each set late to early, and early to late, hanging on the wall for people that had run into the mount swap problems. I probably sold a dozen sets during the late 70s, early 80s time period. After the lease was over (1982) the oil company tore down the old service station, and put up a new self serve kiosk station. I still had people seek me out to buy a set of the adapters for years after I left the service station.

The problem with the thin strap iron was that under severe usage, the mild steel would tend to deform. I never had any breakage, but they would deform somewhat, and bend.

:focus:

Thanks for the feedback, Brad. My plans to only run the 428 in th '70 until the original engine rebuild was done, so hopefully i won't see too much 'deforming' of the bracket.

I have another question regarding the flywheel that i just had redone (and new clutch). My plan was to put that McLeod flywheel back on the 428, get a new clutch, and top that in the Trans Am while i have the original RA III 400 redone. But I would probably want to use the flywheel on the 400 once I get it back, as opposed to using the stock one, which i am sure is what is in there now. Do they need the flywheel to balance everything on the 400 stroker assembly? If so, does that mean I need to buy another aftermarket flywheel? I have the same question regarding the clutch. Let's say I buy a new clutch (since that flywheel can take either a 10.5 of 11 in clutch, should I get the larger one?) and I install the 428 and run around with it until the 400 is done. When I go to put the 400 back in, do I need to install a new clutch? I'm assuming that if I can just take the flywheel off the 428 and bolt it to 400, that will be ok, but just making sure. I don't want to have to buy too many parts to install the 428, because I honestly expect it to only be in use for a couple of months (and winter in NJ is fast approaching). Thanks

Every engine I've had balanced they wanted the flywheel, or flex plate when they were doing the balancing. That said, if the same outfit kept a record of balancing one engine with a flywheel, I would think they could refer to the notes, and balance the next engine with those specs.

I'm not that well versed in engine balancing, but I bet Mike Garblik would have that answer, mgarblik on here is his member name. Maybe he'll see this, and respond.

My Molnar rods arrived a couple months ago for my stroker build, but I’m still waiting for my 4.00 stroker crank (3.00 mains). I want to put the 428 in the Trans Am so I can at least drive it while the 400 stroker is being built bi have the motor mount adapters but now I have a different question regarding the clutch. If I put it in the car with a new clutch and start driving it, but wind up getting my 400/433 stroker done soon, can I reuse the clutch? I can’t imagine I’d put a lot of miles on it between now and when the stroker is done.


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I would see no worries about re-using the clutch.

As long as it's working properly on the 428, you should have no problem transferring it to your new engine. Over 5 decades I've switched them when installing new engines, if I knew the history of the clutch, and visually it appeared fine.

If I hadn't driven the car before the changeover, I might replace it just to save a bunch of labor down the line, but if you know it to be operating well, just swap it.

Thanks for the feedback. I’m almost done with my automatic-to-manual conversion on my 2003 Tacoma. Then I am going to put the 428 in the T/A


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So I started the process of putting the 428 in the ‘70 TA today. First off, the silly question. I thought by buying the adapters to put a ‘69 and earlier engine in a 70 chassis I would use my 70 motor mounts and bolt them to the 69 block, and everything should line up. Do I have that right or should I be using 69 motor mounts? The reason I ask is I had to use a grinder on my 70 motor mounts to get them to fit on the 69 block with the adapter. After that when I went to put the engine in the car, the motor mount holes won’t line up. It says if they are just a little too wide to drop into both frame motor mounts. here you can see the passenger side mount just sits on the frame mount. The driver side mount is lined up. Should I try loosening the frame mount ?

https://uploads.tapatalk-cdn.com/202...e70addd89b.jpg


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Motor mounts are flexible, I've had to use a come along to get them aligned over the years. These are stock mounts, in stock locations, IE a dodge truck.

The makers of todays mounts are precise to within a half an inch, so you have to force them to comply many times. Prybars are sometimes required.

The mounts you use should be for the chassis you're installing the engine in, the adapters make them bolt to the engine you're installing.

Before there were adapter available (1977) I was doing the exact same swap you are, 1969 428 into a 73 firebird. I assessed the problem and made my own adapters, they also required persuasion to get everything bolted together, so I know where you are as far as it doesn't just drop in and everything falls into place. You need persuasion sometimes, sometimes you need a grinder and a hammer, if it were easy everyone would be swapping engines......;)

I would do essentially what Sirrotica suggested;
Sometimes even all the right parts will net a mount sitting like that...

You can see how I mounted the adapter. Hopefully I did that correctly.

https://uploads.tapatalk-cdn.com/202...b6234fb827.jpg


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I’ll try grinding the lip of the motor mount that seems to be catching.

BTW - what are the torque specs for the motor mounts? I read 70 ft-lb, but when I tried that, the lock washer that came with the adapters just split in half. I also read 34 ft-lb but that seems kinda light.


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I've never torqued a motor mount in my 50 plus years of spinning wrenches for a living. I tighten them til they wont back out, and aren't stretching, or distorting the threads in the block. I realize that there is a torque spec for damn near every bolt on an automobile, but looking up every fastener on a car that I worked on, I wouldn't get much accomplished.

I'm guessing, 7/16 coarse bolts, grade 5 would probably be fine at 40-45 lb ft. Take into consideration a 3/8 rod bolt is 45 lbs., but is fine thread requiring less torque than a coarse thread. Fastenal torque table says 42 lbs. so I hit pretty close at 40-45.

Ok thanks!


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