Inliners International Forums General Discussion Engines Bore spacing

Does anyone know the bore spacing on the 235 engines?

The last time I had my 261 apart I made some measurements that showed about 4.20" between the siamesed bores (1-2, 3-4, 5-6) and about 4.38" between the non-siamesed bores (2-3, 4-5). These are at best about +/- 0.025". There was a long thread recently on the H.A.M.B (about installing various heads on a 235 or 261 to get a poor-man's 12-port) where the question of bore spacing came up frequently, but no one ever said what it was with any certainty. Many did not even seem to be aware of the siamesed bores.

Thanks Hoyt. I was talking to a freind of mine today who owns an automotive machine shop. He said he had a block I could borrow. Perhaps I will get it and find out for sure.

When you find out for sure, either confirm or update the figures shown....I want to make a torque plate!Thanks.

ps. Oh yeah, "What happens on Inliners, Stays on Inliners",ya hear me...

I had all the bore spacings etc sent to BHJ Dynamics last summer. they now make a torque plate for the 235/261.

How much are they, do you have any idea.

They are pretty expensive IMHO. As I recall they ran about $500. I would like to have one, but wont use it that much. Unless, maybe, we could talk Brian Clarke (at BHJ) into selling a few to us inliners at a discount..........

I checked the BHJ website, and didn't see one listed for these engines. I did price one for the 250/292 just for reference and they were very pricey like you said. If you have the specs handy that I could put into a blueprint form, I'll see what I can do about making several. Im sure I can make them considerably cheaper than what they will sell them to us for, even in quantity.

You wont see it on the website - you have to call and ask Brian directly. I dom't know if I have all of the info. I can check but i think I threw it as soon as they made the plate

I already have all the coordinates of the bolt holes and will confirm the bore spacing tomorrow. I could make these very cost effectively as I could prpbably fit 40 of them on the surface grinder at once. If the head and the top of the block are skimmed without stress would the torque plate do anything at all? I will be boring a 261 in the future and guess I'll make myself one but am having trouble recognizing the benefit if both surfaces are flat to begin with.

When BHJ made theirs, the had the 261 bore on one side and the 235 bore on the other.

if you make them, let me know the cost - I sure wouel be interested

The reason they are used, I am told, is that when the head is torqued, it actually can bend or deform the cylinders due to the forces of the headbolts. I dont know if it is theory or practice, but that is what I am told

When you torque a cylinder head to a block, the bolts pull the cylinders out-of-round,creating an egg shaped bore, that was previously perfectly round with a fresh bore and hone job. A torque plate is an absolute necessity for any high performance or racing engine because the "plate" simulates the stresses of the bolts being torqued, and a head installed on an engine when the cylinders are bored and honed. So when the cylinder head is actually installed and torqued in place, it makes the cylinders back perfectly round as when they were bored. To see how much of a difference it makes, go to a machine shop some time and watch one being bored w/plates. Many Winston Cup teams have plates that they bolt to every surface of the engine externally to simulate and eliminate this at that extreme of a level. They even circulate heated water thru the water jackets as the block is being bored to simulate the thermal expansion of the block at operating temperature while boring and honing it. Kinda' extreme for us, but they do it because they found it makes a difference and more HP. We found early on with Cotton's 292, that even with a torque plate, we were experiencing an excess oiling in the #6 cylinder! We couldn't figure out why just #6 was always the culprit. We had an extremely tight relationship, with then head engine builder for Donnie and Bobby Allison, Dave Vaselnuick,(if that gives you a time frame of when it was)and he immediately knew what the problem was.....On an inline, more so than a V-style engine, when you install the bellhousing, it in the same way a cylinder head does when torqued, was distorting the #6 cylinder, making it out of round. Dave told Headrick to torque a bellhousing to it when you bore and hone it just like a torque plate for the head. He did,problem solved. Nascar guys were doing all those tricks in the 70's. The bellhousing plate for the inlines is a for real "speed secret" and "trick of the trade" that I could probably charge money for, but its here for free. One final note about Dave, he made the "Alabama Gang"....The "Alabama Gang"! And he is one of the many "links" in the chain that helped put Cotton and Headrick at the top. I had the priveledge of working with Dave for two years in the mid-90's when he was transitioning from California to Charlotte to become knee deep in the Busch and Craftsman Truck series.He headed up a Pro Stock R&D program for Headrick,while he was preparing his own shop in NC. To be in the presence of someone like him day-to-day, was like being amongst royalty. He is still currently dominate in it today....a true unsung hero!

That is a good tip and so easy to use! Thanks!

I immediately decided to print CNC's info. As a layman it's a teaching tool and an eye opener to the intricacy of performance engine building.The personal history of it is just a super plus. In my 60's, and I'm still awed by this stuff.

Drew, Me too! I love this place. There is so much knowledge and experience being shared so willingly it is amazing! Here I am in my 60s and I know just enough to make a total ass of myself! But they still help me!

For me ,what makes sharing these experiences and "jewels" of knowledge enjoyable to me is how much it is appreciated by you guys! Believe it or not, I have tried to interact with other forums in the past just like I am now with Inliners, and have been cussed at,sent threatining PM's, told to find somewhere else to go,told my ideas dont fit their beliefs,blah blah blah. So you get to reap what others have cast away....their loss, but your gain. Too bad for them. I like it here, and like the atmosphere and all who are on this forum. Thanks again for the warm and kind reception you have given to me, that is what has made my experience here on Inliners very enjoyable....Thanks!

You didn't have enough tattoos! Don't you know that automotive expertise is measured by tatt stats?

Oh well, glad to be here!

I'm glad its working out this way. Everyone has different talents and experiences. I dont know much, but what I do know I'm willing to share. Maybe I should get my tat stat up and get more expertise........

Ive been building these motors for years and totaly overlooked the bellhousing-rear cyl. thing! Man you never stop learning on these old things do ya?

I was fortunate to be influenced by such talented people in the racing community! And I am glad to be able to share what I know and have learned to others that could possibly use that info to take their projects to a higher level....

I have some measurements to pass along.

As noted bore spacing is staggered and is:

#1 to #2 = 4.188”
#2 to #3 = 4.375”
#3 to #4 = 4.188”
#4 to #5 = 4.375”
#5 to #6 = 4.188”


Here are the head bolt coordinates numbered according to torque sequence:

1 = X0 Y0
2 = X0 Y-2.050
3 = X2.530 Y-6.088
4 = X-2.530Y-6.088
5 = X-4.279 Y-.286
6 = X4.279 Y-.286
7 = X6.035 Y-6.088
8 = X-6.035 Y-6.088
9 = X-8.557Y0
10 = X-8.565Y-2.050
11 = X8.557Y0
12 = X8.565Y-2.050
13 = X9.670Y-6.088
14 = X-9.670Y-6.088
15 = X-12.561Y-.218
16 = X-12.985Y-5.898
17 = 12.561Y-.218
18 = X12.985Y-5.898


Tolerance on measurements is .005” or less.

Ok Curt, Thanks, do you have the XY for the #1 Cyl. centerline in relation to the X0Y0 #1 bolt. Thanks a bunch....Scott

ps. I can also make a pressure testing plate as well for the head!

considering how little you use a torque plate, we could have a comunity piece and just ship it around to all involved. anyone who wants to use it kicks in or one guy is the keeper of the plate and rents it out.

Its going to weigh almost as much as a head, so by the time you ship it back and forth twice you'll have $100-$125 bucks just in shipping. It probably would be more appealing to the more hard core builder/racer to buy one just because its doubtful most any race shop could provide a customer with this service because they themself dont have a plate for some of the more unique engines like these. Now that I have the coordinates from Curt, I can generate a program to make some, and so can he. I think that either of us could make them a lot cheaper than BHJ can sell them to us for, just because we each have access to the CNC equipment to do it with. But renting them is a possibility too ,if the shipping doesn't become too much of an issue for some....

CNC, Have you thought of doing a lifter bore alignment tool?

Would it be possible to make a torque plate from an old head?

I have, and also possibly boring the lifter bores to accept a standard size SBC lifter(roller), so it would possibly open that door for more people to economically use a roller cam, instead of having to search for 50 year old used ones that seem to be non-existent. Trying to find original blueprints to accurately make a tool like that would be difficult to find. Also,I've found that using a block to create the dimensions doesn't really provide an absolute way to reverse engineer the dimensions on some things as critical as this. What if the block you chose was flawed in that area, how would you know? You could possibly check and dimension 8 or 10 blocks to try and determine an average to be more accurate. In my area, all I seem to be able to find are 216's. I have also considered making some billet main caps, and also a boring bar to bore the cam tunnels to install roller cam bearings. I will have to make a boring bar and the alignment rings for the mains first, so if I do make some main caps,I can also put them on the block. There are just so many practical high tech ways to improve these engines with these 21st century concepts. I was just pondering the lifter bore idea today, we must be on the same wavelength. There's a race shop local to me that has the BHJ lifter-tru set up for a SBC, I need to look at it and get some ideas. Thanks for confirming what I was already thinking, I think were cookin' with Crisco now!

You could get close, a block would be better because with a head you dont know where the cylinder bores are in relation to the bolt holes. Curt just posted the bolt hole coordinates for me(us)for the 236/261, if he can give me the #1 cylinder reference to the
X0Y0 location, its a done deal. Its that easy. Dont worry Beater, Im going to do a torque plate for a GMC too,I just need to find a block for one....

I've got a striped 302 in my shop but I'm too ignorant to take any meaningful measurements.

If I had a new head gasket,It would probably be a good alternative,I just thought of that....

I've got a pile of NOS gaskets that are not good enough to put on an engine.

If you have one that is in good shape, and not warped up or bent and deformed, would you care to send it to me!

Sure! I'd be glad to. I'll pull one out tomorrow morning.

You guys RULE! I never thought my question would lead to all of this. Keep it up.
Thanks, Ron

Bolt holes 1 and 2 are centered between bores 3 and 4 so the cylinders are equally distanced from there. Cylinders 3 and 4 are each 2.094” from the centerline of the bolts so this places cylinder 1 at 10.656” on the X axis from head bolt 1.

Doesn’t the torque plate need to have a bore that’s larger than the cylinder to let the bar pass thru? I was thinking of using Hardox wear plate as our cutting table frequently makes chunks of scrap that cost me next to nothing and that stuff is super tough. Luckily I have an engineering department to advise me on material and thickness to be sure.


I checked the head gasket I have (which was stamped GM Canada) against measurements on the head but a few places on the gasket have a large triangular hole at the bolt location preventing a positional measurement.

Thanks again Curt, your right about the bores in the torque plate. They typically are larger than the bore by about .100-.125 of an inch to allow the bar and honing stones to pass through without contacting the plate. You could probably use a head gasket as a reference and make the bores slightly smaller than the bores in the gasket. Most times an old gasket is also used to torque the plate to the block when boring and honing as well. The thickness of the plate is generally in the 2-1/2"-3" range, and the materials are billet steel but not heat treated, and BHJ also has some that are cast iron. They also offer an aluminum plate to simulate engines that have and are using aluminum heads. Hope that helps, thanks again for the specs! Scott


ps. So that we are on the same page, the bore centerlines are going to be Y-2.050, same as the #2 bolt....

I keep saying Inliners has it "goin on". Be careful what you ask for(LOL)!

Whoa! Sorry, bolt 2,10, and 12 are NOT on the bore centerline. I can't get that dimension off the head and will have to get it off the block this evening and get back to you with a y axis number tomorrow.

P.S. the bore holes in the gasket are not round- they're shaped like the combustion chamber.

Ok,thanks! Just make the bores in the torque plate about an 1/8" larger than the bore size you are going to be using! This will also give you some wiggle room for future overbores as well.

ps. Its hard to determine the bolt locations in relation to the bore centerlines with just a cylinder head. Since you have access to the CMM,it should make short work of it. I doubt that a Stovebolt has ever been measured so accurately and precisely. I'll be looking for the Y centerline reference,Thanks....