Can someone post a link to the article that shows what angle to drill the holes in an 848 head for use on the 261 engine? Somebody posted some pictures of a cutaway head that shows the angle the holes need to be drilled to intersect the coolant passages properly, but I can't seem to find it today. Thanks! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thank you, Jerry, for calling the extra holes "extra coolant passages" - I cringe when people call them "steam holes" - if you got steam, you got something wrong.
Click magnifying glass symbol under your name top right , then under it again and then click search without entering any information and it will bring you to the search screen.
Thanks! Got it bookmarked now! I'm going to be building a couple of "261's" before too long, (more like closer to "300") and I might be using 848 heads, or possibly milling one of the earlier low compression 235 heads to get the same compression ratio. Either way, I'll need to drill those holes. The standard 261 head with the holes already there can also be milled to duplicate the 848 combustion chamber. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks, all! I'm thinking of making a jig using hardened drill guide bushings in a bolt-on steel plate to take the guesswork out of drilling a head. I believe the head bolt holes adjacent to each pair of holes are similarly positioned, so the jig would only need to be 2-3 inches wide or so, and use head bolt holes for attachment. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks, all! I'm thinking of making a jig using hardened drill guide bushings in a bolt-on steel plate to take the guesswork out of drilling a head. I believe the head bolt holes adjacent to each pair of holes are similarly positioned, so the jig would only need to be 2-3 inches wide or so, and use head bolt holes for attachment. Jerry
The head bolt holes are not symmetric around each pair of holes.
I can see head bolt holes and coolant passages that could be used as alignment points for a drop-in jig. Use close fitting dowels to engage those holes, and one jig could be used for all three pairs of holes. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The 3 coolant holes (approx. 3/4" diameter) are rough cast, have a draft angle, and unreliable position. Good luck with a close fitting dowel. The head bolt holes are a different story...I digitized several heads to determine exact position of the head bolt holes in order to make a torque plate. Position was within .005" on all of them so I consider them a reliable datum. If I wanted a jig I would bore 4 headbolt holes, drill the 6 angled holes and then gas nitride it rather than install drill bushings. Jigs with crude datums give crude results.
Yep, gotta get those coolant holes positioned down to the thousandths- - - -most people get the job done by eyeballing with a hand drill motor! "Measure it with a micrometer- - - -Mark it with chalk- - - -Cut it with an axe!" LOL! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
One way to have it done is to wipe a little dykum in between the cylinders, lay up a head gasket, with bolts and washers to position and secure the gasket to the head, center punch where the holes need to be located, then find a machine shop that still has the air table/valve head reconditioner (I wish I know what it is really called but it is ancient technology for doing valve jobs), where the air table can be positioned at the correct angle for drilling. Let me look for a couple of photos I think I have of the head I did this past summer and the drilling of the holes. Not fancy but got the job done.
My young machinist doing his thing on one of my heads!
It's called an "air float" table, and I've got one on my valve seat and guide machine. Air hockey on steroids!
Yep, that's a machine exactly like one of the two I've got. The older one doesn't have an air float- - - -yet. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Alvin, I've got at least three ways to position the holes accurately, just like I've got several ways to drill and tap the snout of a crankshaft. As always, I'm thinking of the guys who don't have a full machine shop at their disposal. Making simple little jigs to avoid ruining an expensive part is just as much fun as using several thousand dollars' worth of machinery to do the same job. I'm not quite as much of a snob as some of the guys with all the toys!
I wonder what happens to all those original 261 heads that the people discard when they're searching for an 848 to modify? It's a very simple procedure to mill the head down to the same combustion chamber volume as an 848, and correct the valve position and rocker arm geometry. Ditto for the pre-848 passenger car and truck heads! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The 848 head is specified at 79.1 cc. That is GM's engineering specification that Tom Langdon obtained for me way back in the 80s when he was still working for GM. The 261 heads are 86.3 or something along those lines. I have to go back and look at my notes as there may be one casting that is even larger. You can mill the 261 head down to get the combustion chamber in that range, or maybe even machine the deck of the block to up compression and improve quench, but you run head long into additional machine work. If you say mill the head, you generally have to sink the intake valve in the head the same amount. Not terrible in terms of machining but just more work to be done. You then have to shim the rocker stands the same amount, and add a lash cap of the same thickness to the tip of the exhaust valve, or order longer small block chevy valves (if you can find them in the right size). Again, not overly complicated but it seems to me using the 848 head and drilling a couple of holes is the less complicated path.
Btw, the 848 head was introduced for the 1956 pass car model year and was advertised to boost the compression to 8.0. In 58 or 59, I forget now, the compression specification jumped to 8.5. I have cc'd a few heads and I was never able to discern a difference in the 56-57 head to the 58 and up head to explain the jump in compression. The stroke is the same, the compression height of the pistons all seem to be the same, all years seem to sit about .115 in the hole, so I cannot say why we go from 8.0 to 8.5 except maybe someone at GM goofed in their calculations or decided to use new math to come up with a more impressive figure.
Am I dating myself when I refer to "new math," lol.
Mike, I have the equipment to machine a milled head to work correctly, and 50+ years of experience making parts fit that were never intended to work together. I'm not suggesting that the average "bolt it together and hope it works" guy should attempt the stuff I do as a matter of routine. When the "hobby stock" round track class I was building engines for wouldn't allow the 64 CC "camel hump" heads on small block V8's, we simply took the 76 CC "smog" heads and angle-milled them .100" to get 60 CC! Then we milled the intake manifold flanges to match the slightly changed angle of the heads, and went out and won a bunch of races. Ray Charles could have caught the modification, as the edge of the head casting was noticeably thinner at the spark plug side, but all the dummies in the tech inspection line did was check casting numbers. Like Smokey Yunick used to say- - - -"It's only cheatin' when ya get caught!" I also had a way to dramatically increase the airflow through the Holley 7448 350 CFM 2 barrel carburetor they made us run! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I am with you. The issue today is finding a machine shop, let alone finding one that will tinker with this stuff. I am lucky, a friend of mine owns the machine shop I use. the young man in the photo is his son and he loves to tinker. Rare is all that I can say.
You can actually angle mill the early chevy 6 head. It does help with the horrendous short side radius issue and the 90 degree back wall. But then you are into spot facing the head bolt holes, drilling the head bolt holes, modifying the push rod holes in the head (to fit 3/8 push rods and to accommodate the angle milled head). But really, this kind of stuff is for all out race motors and since there are no longer any competitive racing classes for these old motors, other then say Bonneville or other land speed vintage class races, its a lot of work for some mostly minimal returns.
Me, I think the money is better spent on the rear seal conversion you have sorted out. There is actually a you tube video showing the process but sadly, the man that did the video passed away very unexpectedly. Pop up pistons would go a long way in building a little more usable power. Forged are available from Ross and Venolia but pretty good money. God I wish Jahn's Pistons was still in the business of selling cast pistons or someone unbelievably turns up with his molds for the pop up cast pistons.
What I think would be fun, would be to sort out a way to use say the 292 rod in a 235/261 block and some common off the shelf pistons that would essentially give you a stroked motor, zero deck, with just a minimal amount of decking. I know the caddy piston conversion, but that piston is really hard to come by, required the blocks to be bored out pretty good, and could only be used in a 261.
To sort out a way to easily and reasonably stroke a 235 using common off the shelf parts, and get the compression up to say something along the lines of 9.0 9.25, I think that would be a really nice improvement for vintage cars and trucks power wise. I wish I was more proficient with machine work, measurements, parts books and specifications.
HRL and I had a lengthy back and forth a few years ago about the 292 rod in a 235. I don’t remember if it was in a thread or in the PMs. IIRC, we had identified some candidate pistons with a proper compression height to make it all work, perhaps with some custom machining to fit the wrist pins.
He probably remembers the details. I can go searching for it.
I'm actually using 292 rods in a full oil pressure 235 conversion of a 216, using a 235 crankshaft and pistons in the 216 block. I make thrust washers to weld onto the 292 rod caps to center them in the 235 journals and then balance the rod assemblies for equal big end weights. PM me an email address and I'll send you some pictures. It's possible to use stock pistons and 292 rods in a stroker 235 or 261 engine by altering the stroke to fit the rod length and wrist pin height of the 292 rod. Since the 261 uses a wrist pin the same diameter as the 292, you can press fit the pins. On the 216 and 235, put a bushing in the 292 rod and make Teflon wrist pin buttons to center the pins in the cylinders.
I'm designing a stroker 261 using H beam racing rods for a Nissan 2.4 liter 4 cylinder engine that will get close to 300 cubic inches, using the same weld-on thrust washer concept for centering in the rod journal. Those rods are 6.5" long, and the rod journal size will allow a stroke increase out to around 4 5/16".
The best way to increase the compression on a stovebolt engine without buying pistons that make your checkbook need CPR is to cram more cylinder volume into the same head. 30 or so more cubic inches in any engine makes for some very nice compression numbers! With the right bore and stroke combinations, I can put 258 cubic inches into a 216 block, around 270 into a 235, and 300'ish into a 261, all with stock pistons! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I would love to keep this issue afloat and continue investigating the possibility. There just must be a simpler solution then having to custom make parts. I have a friend of mine who builds race cars, fabricates parts, roll bars. He makes it look simple but the reality is that its not. I think it s the same here. It would be kind of cool if we were to sort out a easy way to increase the cubes and compression with swapping parts and basic machining. Give a lot of 235 motors and the trucks they are installed in a little new life and maybe a more comfortable ride on the highway with a bit more power.
There's no substitute for cubic inches (or dollars). Getting the crankshaft ground to the right stroke and rod journal diameter is the biggest challenge- - - -that's why I bought two crankshaft grinders a couple of years ago. Maybe someday before I get too old and feeble to work in the shop, I'll get everything up and running and start turning some of these Rube Goldberg pipe dreams into reality. I don't have any "trade secrets"- - - -I'll gladly share ideas and dimensions with anyone who will take the time to communicate with me! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I'm actually using 292 rods in a full oil pressure 235 conversion of a 216, using a 235 crankshaft and pistons in the 216 block. I make thrust washers to weld onto the 292 rod caps to center them in the 235 journals and then balance the rod assemblies for equal big end weights. PM me an email address and I'll send you some pictures. It's possible to use stock pistons and 292 rods in a stroker 235 or 261 engine by altering the stroke to fit the rod length and wrist pin height of the 292 rod. Since the 261 uses a wrist pin the same diameter as the 292, you can press fit the pins. On the 216 and 235, put a bushing in the 292 rod and make Teflon wrist pin buttons to center the pins in the cylinders.
I'm designing a stroker 261 using H beam racing rods for a Nissan 2.4 liter 4 cylinder engine that will get close to 300 cubic inches, using the same weld-on thrust washer concept for centering in the rod journal. Those rods are 6.5" long, and the rod journal size will allow a stroke increase out to around 4 5/16".
The best way to increase the compression on a stovebolt engine without buying pistons that make your checkbook need CPR is to cram more cylinder volume into the same head. 30 or so more cubic inches in any engine makes for some very nice compression numbers! With the right bore and stroke combinations, I can put 258 cubic inches into a 216 block, around 270 into a 235, and 300'ish into a 261, all with stock pistons! Jerry
You have to offset grind the crank, correct? Is that something the average machine shop does on a regular basis?
The only machine shop here in middle Tennessee that I know of willing to do that is run by a "retired" machinist two years older than me. He has a nicely-equipped shop behind his home, and he stays booked up at least six months in advance. He's almost 100 miles north of my place, up close to Kentucky. He also makes welded strokers for the big 2 cylinder John Deere tractor pullers in the antique class, ones that require slots to be cut in the block between the crankcase and the transmission housing to accommodate the 5/8" extra stroke.
Stroke changing used to be commonplace in the flathead Ford days when Dad was racing, and early Chevy 350's could be stroked to 3 9/16" by offset grinding to use the 2" diameter 283 rod journals. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
