Engine mounts for 70 SBC question
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Engine mounts for 70 SBC question
With rubber engine mounts in good condition, how far would you expect the engine to move if you put the trans in drive, stand on the brake and then give the engine some gas?
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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The engine will move a little but as long as the fan doesn't hit the shroud I'll guess that your good.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Seems I'm not then, its moving about an inch or more. The fan doesn't hit the shroud because it is set back slightly, but the air cleaner is hitting the hood! the chassis in this frankenvette has a std engine mount on the RH side but on the left is fitted with what seems to be a C2 engine mount as it does not have the safety fitting and is slightly narrower across where it fits onto the chassis. I have looked inside the chassis rail with a camera but cant see any sign that the rail has been altered or a section replaced. I have removed the RH engine mount and it is not torn but does have some cracks in the rubber. I will have to decide whether to replace it with another C2 mount or adapt the correct C3 one to fit somehow.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
It shouldn't move anywhere near that much....maybe 1/4" or so. That much movement would indicate some separation of the rubber in one or more mounts. And I don't think it would more that much with both engine mounts in good shape. How do you know they are good? Are the mounting bolts torqued up?
Last edited by 7T1vette; May 10, 2016 at 12:02 AM.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Hi 7T1vette, I don't know if the mounts are good other than the rubber is not completely torn up. Looking at the locking mount shown in Peterbuilts second pic it has 2 packing pieces welded in to give an inside dimension of 2 5/8. The one I bought only has one packing piece per side giving an inside dimension of 2 15/16 and according to the shop is the correct item. I say it should be the same as Peterbuilt's pic. I also have a new non locking mount for a C2 and it is 2 5/8.
So, I will make a couple of packing pieces and weld them in to correct the dimension (you cant just go down to a local shop and pick up components here).
So, I will make a couple of packing pieces and weld them in to correct the dimension (you cant just go down to a local shop and pick up components here).
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
With old mounts, you can actually have the rubber become un-bonded to the metal. One of the mounts will be in 'compression' when the engine revs, so there will be no problem with that one...even if it has problems. The other will be in 'tension' and you might actually see the engine "lift" off the mount when you rev it.
Just because the rubber "looks" to be in good condition doesn't mean the mount has any integrity. You can also use a floor jack (carefully with wood block to lift on side of oil pan rail/bolts) to lift each side of engine (separately) to see if mount has separated.
Just because the rubber "looks" to be in good condition doesn't mean the mount has any integrity. You can also use a floor jack (carefully with wood block to lift on side of oil pan rail/bolts) to lift each side of engine (separately) to see if mount has separated.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
So, the engine mount on the LH side was a C2 style one that incorporated no lock, the RH one is the correct one with a lock. The engine moved enough to push the air cleaner nut into the hood and crack it. I am changing both mounts but figured that since the hood is damaged it might be worthwhile altering the hood to give more clearance since the air cleaner was almost touching it anyway. I was thinking of adding the hood scoop for an L88. Does anyone have a how to on this project? To add to my list of projects it turns out that the vacuum reservoir has a crack in it, which probably explains why I could never get a totally smooth idle.
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