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Jul 21st, 2025 | | | | Joined: Jun 2016 Posts: 222 DLBrooks | | DLBrooks Joined: Jun 2016 Posts: 222 | I have a 1954 261 head casting 3703570 that I would like to put on a 1953 235 pg engine. If this change has no ill effects do I need to drill the 235 for the 261 head steam holes or just leave 235 block as is? -- I know what the steam holes are for on the 261 siamesed cylinders..
Do I use the 235 head gasket or the 261 head gasket?
The 235 needs a valve job and I have a good reworked 261 head. I am not after added performance except good valve sealing on all cylinders.
Last edited by 42465967; 10/05/2018 11:04 AM. Reason: words
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | There will be a slight loss of compression if you're replacing an 848 head with the 570. No, there's no need to drill the 235 block for the holes in the 261 head- - - -they would serve no purpose since the 235 is able to flow coolant between the cylinders. Use whatever gasket is handy. Without the corresponding holes in the head and block, there's no reason to worry about whether or not the gasket has holes in it. I'd suggest using the 235 rocker arm assembly to be sure the rocker oiling system stays the same.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Jun 2016 Posts: 222 DLBrooks | | DLBrooks Joined: Jun 2016 Posts: 222 | I will verify but I do not think I have an 848 on the 53 235. I do plan on re-using the 235 rocker arm assembly. Thanks HL. | | | | | Joined: Sep 2001 Posts: 29,262 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,262 | One of the 1953 high-pressure-235 PG heads was 3838066.
The "848" heads started in 1956.
You will want-to/have-to use the 261 valve cover (unless you change-over the two 1953 valve cover "stud posts" from the 235 head), | | | | | Joined: Jun 2016 Posts: 222 DLBrooks | | DLBrooks Joined: Jun 2016 Posts: 222 | I have the 261 valve cover but probably will see if I can use the 235. In fact I have the whole long block 261 less solid lifters, pushrods, and solid cam. I will determine if the block just needs a crank and bearings or if other probs. Had been rebuilt --dunno who --- bored 40 over --- hone marks still visible in the cylinders. I have not looked yet but supposedly main bearing clearances did it in.
Also with the 261, but from a 235, I did get a new hydraulic cam, new hydraulic lifters, and new pushrods for a 235. Also got the rocker arm setup for a 235. gimmes
Last edited by 42465967; 10/05/2018 11:14 PM.
| | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | Make sure your distributor gear is compatible with the new camshaft, not a good idea to have a steel gear on a cast cam or visa versa. I believe 53 and earlier cams were steel and later were cast, so if you are using the distributor from the 53 engine it will have a steel gear.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Nov 2016 Posts: 22 'Bolter | | 'Bolter Joined: Nov 2016 Posts: 22 | Which head gasket? 235 or 261. | | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | Either head if going on a 235 should use the 235 gasket
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
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