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#1
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Frame Mount Issues - Poly vs. Solid
I have a 1981 TA with a 1976 455, and I want to replace the frame mounts/
The polyurethane inserts would reduce engine rock, which I need, since air cleaner to hood clearance is minimal with the Northwind intake. I purchased the Butler polyurethane frame mounts , but the tabs in the insert, that the engine mounts' rest on, come sawed off. I am not sure the engine mount would fit with them not cut off, so this may be correct. Has anyone used these Butler polyurethane frame mounts? Installation instructions say it requires the weight of the block to be used to compress the "clamshell" before tightening the frame mount to the frame. That seems difficult... I have Dougs ceramic headers, but how big of a problem is this heat issue...melting the polyurethane insert? Solid mounts are looking better all the time, but I am unsure of the pros and cons of going that route.. |
#2
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Because of the tendency of Pontiac blocks to split in the middle, I would recommend against solid mounts at all costs. Tying the left head to the frame negates putting all the strain on a small area on left side of the block by using solid mounts. Tying down the left cylinder head spreads the force over 10 head bolts and through the coolant crossover over to the other side (passengers side) of the engine. It's your car, and you can do whatever you decide to do to minimize engine movement. I'm just relaying what has worked for me for roughly 45 years. |
The Following User Says Thank You to Sirrotica For This Useful Post: | ||
#3
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I am interested to see feedback.
I've read on this forum that the solid mounts can flex the block. There was a thread with 1 or 2 photos of blocks cracked in that area where the mount is. I am sure it depends on power level too. |
The Following User Says Thank You to ponjohn For This Useful Post: | ||
#4
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There are more than 1 or 2 pictures around of cracked blocks, those were the ones I was able to find quickly from Troy Tribby's 60 Pontiac race car. Troy attributed it to solid mounts and went with a plate system after destroying his engine.
Pontiac knew that there was a possibility of splitting blocks in at least 1970, that's when the redesigned the mounts on the new 455 to spread the load over 2 bulkheads in the block ,#2 and #3, rather than only #3 in the early 2 bolt design. If the Pontiac engineers were concerned enough to redesign the motor mount system they're were smarter than I am. If you're stressing the engine further than say 25% over the intended design you're tempting fate with solid mounts in the stock location, IMO. As I said, it's his car, he can totally disregard the information I provided if he wants to. |
#5
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I run stock mounts on my 66 race car with a 3/8 Chrome Moly Rod and Heim Joints. Bolted to a bracket on the frame and the cylinder head. Running over 790HP in a factory block at 7200 RPM. Limit the movement at the front. The rest is just along for the ride.
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66 GTO Nostalgia Super Stock/Street Legal Car 421 CID, stock block, Wenzler Intake, 2- Carter 750 AFB's, 3.90 Gears, Full Factory Interior, Full Exhaust, Stock Suspension 3750LBS 9.77@136.99 Multiple NSCA/NMCA World Champion 66 GTO 389 3x2, 4 speed, 4.33 gear, Montero Red 33K original Miles 67 GTO 2dr Post, 428, Tri Power, 3.55 Gears 80 Trans Am Black SE Y84 W72 WS6 |
#6
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at what power level or et's are blocks splitting with solid mounts? i agree a turnbuckle is a good idea, i run a chain on my 500+hp 72 firebird due to the weak style mounts it has along with home made beefier mity mounts.
however this is the street section & i doubt he is making big enough hp or heavy racing to split the later style 1976 block since he didnt mention that was his concern for the poly mounts. & being he already bought them & is asking for suggestions from others that have actually used them, hopefully he can get some feedback related to his question. |
#7
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My motor ran solid mounts for many many years in it's previous car...which was a track car...slicks etc...with no issue.
So that option is on the table...but I am 90% street now. I do not want to say how much is cost me to get these poly mounts and bolt kit from Butler shipped to Toronto...it was insane. OK I will tell you...$250CAN...via UPS... But I did not expect the mounts would be so much different from stock, or that the Butler bolt kit was not compatible, or there are heat issues with poly. Wish I had asked the forum earlier...turnbuckle would have saved a lot of headaches and $$$. So no one has any experience with the poly mounts? On the stock frame mount, the engine mount rests on the metal tabs. With the poly, they arrive with the tabs cut off so all the weight rests on the bolt, which seems like it would be prone to excessive wear. |
#8
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The mounts appear to be for the "adapter kit" and if I am seeing Butler's pictures correctly, the mounts are wider apart and would make sense as to the longer bolt.
Don't know what frame mounts you have installed from what year? That may be where the issue is? If they fit the block, and drop into the frame mounts, then they should be good to go. Use your shorter mounting through bolt and go with it. Poly will be stiffer/harder than rubber, so not as bad as a solid, but not as cushy as a factory rubber mount. Some like to mix/match using the poly on the drivers/torque side and rubber on the passenger side. The engine limiter can be a good idea on bigger HP engines, clutch cars, with good traction tires. If all else fails, call Butler. |
#9
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All has worked fine.
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-- James Work '67 GTO Convertible "Koerner Built 413 500 hp with a Victor!.. I'll run a stock intake." '75 Formula 400 - Daily Driver - Running with my Home Built 455 and TH400 Details here: http://forums.maxperformanceinc.com/...d.php?t=588372 |
#10
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I have done the chain, the cable, and the "fork" and "slotted plate". The last has the easiest adjustment and seems to do the job the other systems did in the past. I have had a retention device on my engine since the late 60s when the Chebby mounts were failing and I did not know if the Pontiac mounts would fail like the Chevy mounts. Tom V. Lots of higher RPM Launches, 2 Muncie Trans failures, 3 8.2" Pontiac rear axles, 1 Chebby 12 bolt axle failure, THEN I WENT FORD 9" AND HAVE BEEN THAT WAY FOR MANY YEARS. The retention devices work.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#11
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So sawing and forcing and beating them into position is a result of the basic mis-application of a Chevy mount into a Pontiac. You'd think Pontiac specialists would know better. |
The Following User Says Thank You to Schurkey For This Useful Post: | ||
#12
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Hopefully, somebody who is actually using the poly inserts in their clamshells will say how well they work.
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Steve F. |
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