Big block motor mount question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**402Bowtie** · 07-12-2005, 11:46 PM

I have a 396 big block that I want to put in to my '72 k20. Do I need the crossmember from the big block truck or will the crossmember from the 4wd truck work? Depending on which crossmember is used, do I use big block mounts or small block mounts? If it makes a difference, consideration must also be given to the fact that it seems like header clearance problems are often an issue with bb engines in 4wd's. Thanks...John

**kwmech** · 07-13-2005, 12:33 AM

A few people before have said they have used the later model x-member. Say out of a 73+. I know the factory member will have oil pan clearance problems

hotrodmtodd · 07-13-2005, 08:09 AM

I just bought a 4X4 XM from Erick (Bisquik65). The way he explained it to me was: You need to use a car type oil pan on the BB for clearance. He also said that there is plenty of clearance for the exhaust as well. You can use the modified SB (cheaper) motor mount rubbers that are in the FAQs. I'm sure ALL this info is in the FAQS somewhere. I am curious to see the oil pans side by side.

Livrat · 07-13-2005, 02:36 PM

I have done numerous BB conversions on 4X4's.. You can use the stock small block mounts and crossmember, But you need an oil pan off of a Chevelle or truck.. Not one off of a Impala unless you modify the crossmember (I have a modified crossmember and a chrome "Impala" pan I just took off my Suburban)
Most of the imported chrome big block pans are the "Impala" ones...
You will have some firewall valvecover clearance issues unless you have a body lift..
My personal favorite way is to use the stock crossmember, truck style oil pan, and move it all forward 2 inches.. You will have to redrill the holes for the crossmembers. and shorten your front driveline and build a new rear one..
Also could put it all in at the stock location and either custom cut and weld the firewall.. or just pound it back for clearance but thats the ugly way..
You can also use a crossmember and mounts from the 73 up 4X4's.. the holes will need to be drilled.. again watch for firewall clearance..
Depending on which header you use.. some have frame clearance issues.. I am running Doug Thorley Tri-Y's on my 68 GMC 4X4 and had to dimple three tubes to clear the frame.. One conversion I used Hooker Chevelle headers.. the clearance for the frame was good, But had to cut off the collectors and tilt them upward to clear the trans crossmember..

07-12-2005, 11:46 PM	#1
402Bowtie Registered User Join Date: Sep 2003 Location: Wichita, KS Posts: 3,735	Big block motor mount question I have a 396 big block that I want to put in to my '72 k20. Do I need the crossmember from the big block truck or will the crossmember from the 4wd truck work? Depending on which crossmember is used, do I use big block mounts or small block mounts? If it makes a difference, consideration must also be given to the fact that it seems like header clearance problems are often an issue with bb engines in 4wd's. Thanks...John

07-13-2005, 08:09 AM	#3
hotrodmtodd 'Burban Legend Join Date: Apr 2005 Location: Mingo Junction OH Posts: 918	What I Have Learned I just bought a 4X4 XM from Erick (Bisquik65). The way he explained it to me was: You need to use a car type oil pan on the BB for clearance. He also said that there is plenty of clearance for the exhaust as well. You can use the modified SB (cheaper) motor mount rubbers that are in the FAQs. I'm sure ALL this info is in the FAQS somewhere. I am curious to see the oil pans side by side. __________________ '67 Chevy Iron City Beer Truck (9ft step) '67 Chevy Panel Truck 467 '68 Short Fleet 305v6 '68 McLaren Ramp Truck '68/'68/'70/'71 Burbs 292/366/402/454 '69 C-30 dump '71 C-50 dump and church bus '71 4x4 454 '72 Blazer (w/pop-up camper) $15 x-hooks '66 Chevy II 194/Weber '68 El Camino" 305v6 '69 Skylark 455 Buick '70 Chevelle 427 '71 Cutlass W-31 '71 GTO 400 2x2 "The 51" Chopped '51 Chevy (409) my first car OK Toad, we'll take 'em all... John Milner

07-13-2005, 12:33 AM	#2
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,641	A few people before have said they have used the later model x-member. Say out of a 73+. I know the factory member will have oil pan clearance problems

07-13-2005, 02:36 PM	#4
Livrat Member #1049 Join Date: Jun 2000 Location: Troy Montana Posts: 3,940	I have done numerous BB conversions on 4X4's.. You can use the stock small block mounts and crossmember, But you need an oil pan off of a Chevelle or truck.. Not one off of a Impala unless you modify the crossmember (I have a modified crossmember and a chrome "Impala" pan I just took off my Suburban) Most of the imported chrome big block pans are the "Impala" ones... You will have some firewall valvecover clearance issues unless you have a body lift.. My personal favorite way is to use the stock crossmember, truck style oil pan, and move it all forward 2 inches.. You will have to redrill the holes for the crossmembers. and shorten your front driveline and build a new rear one.. Also could put it all in at the stock location and either custom cut and weld the firewall.. or just pound it back for clearance but thats the ugly way.. You can also use a crossmember and mounts from the 73 up 4X4's.. the holes will need to be drilled.. again watch for firewall clearance.. Depending on which header you use.. some have frame clearance issues.. I am running Doug Thorley Tri-Y's on my 68 GMC 4X4 and had to dimple three tubes to clear the frame.. One conversion I used Hooker Chevelle headers.. the clearance for the frame was good, But had to cut off the collectors and tilt them upward to clear the trans crossmember..



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