Inliners International Forums General Discussion Engines 235 teardown/261 swap

Well its been a crazy day and the tear down of the body/front end of the truck has gone great, and easy mostly because the guy that I paid to do the body work did such a crappy job putting it together-and I mean scary bad, bolts without nuts for the fenders and all, yeah I cant believe I drove that thing home, good Lord. Anyhow it has become apparent to me that I can not get that motor out without taking the flywheel off because of the narrow opening on the bellhousing on the motor side, so I gotta disconnect the bellhousing and slide it away from the tranny, which i put a jack stand under so it doesn't do a humpty dumpty of the ground when it does disconnect, figured I would keep ya guys posted on the progress, any tricks or hints to make the deal easier would be neat to hear, see ya on the board.

What year truck, what year engine? Are the motor mounts for the old and new engines the same? If not, you'll likely be in and out a couple times before you're done. Took me twice, in to measure and mark, out to fabricate and install mounts, and then in again. Course, it'd been 40 years since the last time I made a switch like that.

Most of the time, you'd slide the trans back and leave the engine/bell housing as a unit until they're out. Depending on year, sometimes it's easier to leave the trans on the engine/bell until the whole thing is out.

for a 47-55 truck,
pull the radiator
pull the tranny
remove clutch & flywheel
pull engine with the bell attached.

Since I have to refit all of my fenders, and rebolt them-both inner and outer. I did take out the radiator, I also have the transmission and drive line on jack stands so they will stay in place and I can just drag the motor out the front. I actually broke one of the bellhousing bolts that's like 6 or 8 inches long, and that thing was a big bolt! I felt like Hercules! so now i just got to rip off the manifold and separate the headers from the downpipes, I already disconnected all the wires and what not. I am just gonna take the bellhousing with the motor, clutch and all hopefully. I realized that the flywheel was too big to make it through the front of the bellhousing, and the clutch is attached to the flywheel, so it follows necessarily that the tranny and the and bellhousing were gonna be complications, so off I go to see if I can get this thing yanked out. BTW my truck is a '56 chevy shortbed, '56 chevy 235 i believe, has the front motor mounts, and a 3 speed overdrive manual transmission.

well that mother is out, and all of the front end is off right down to the bumper and radiater support brace, not bad I think for 3 hours today and 2 yesterday. All went pretty well, no major hang ups, hopefully the new motor goes in just as smooth-knock on wood huh!

Hello again gents, I thought that I would share a rather interesting car building experience, and I don't know if this experience is universal or not. It seems that every time that myself or my brothers are working on our rides, and a hood goes up, people start burning out and going insane on our street, we also happen to live by a stop sign, right on a four way corner. This always happens! Does this happen to anyone else? I was talking with a friend across the street and a 13 year old 110 pound kid proceeds to start dropping the F bomb and telling some 19 year old sales man that he was gonna beat him up, this kinda junk always happens when hot rods are being built here, I just don't get it-and why don't kids have any respect anymore? As if this wasn't strange enough, this kid then decided that since I was standing there with a cro bar to make sure nothing crazy starts, from there apparently I was a wimp, and he started talking smack to me about how I'm a chump, but I am like 300 pounds, and 6'8 who happens to be a Jiu Jitsu instructor and trains in Muay Thai-so he didnt hang around long, in fact his talk was done as he was riding away, it put such a damper on my wonderful progress for the day, similar stories anyone?

That does sound like wonderfull progress.

Is it possible maybe you're only noticing it when you are in your garrage / dirveway (or wherever it is you are working on this)?

It's a shame about the 'bratty' behavior of the 13 year old (sounds like he's a 'time out' kid; I would have got my but kicked for that, then a whupin' when I got home too, my how times have changed ).

As far as the 'stupid driver tricks' my stuff is hard enough to see from the street that I don't personally have that problem but I have heard of that kind of behavior (revving engines as they pass, burnouts, or as you describe, alsways leaving the stop sign like it's a 'Christmas Tree') from many people.

Even to the point of, if their garage door is open (tarp is off, whatever it takes to make it visible from the street) that it's like a switch for such behavior.

Kinda like a full moon, people only act goofy if they can see it.

Keep up the good work.

when I break this motor in for the first twenty to break in the cam should I use a thermostat? and if so which temp like a 160, or a 180?

I would break it in with whatever you plan on running with. But then that's me and I use the more expensive 'balanced flow' (forgetting the other names at the momnet) type, if it fails, it fails 'open'. It also maintains a more constant temperature.

well I think I hit a strip of luck, When I pulled the pan the other day and took out the old 235 oil pump and looked at the oil screen and pump to block tube, they appear to be a match for my 261 in that all the fittings hook up and are the same size and appear to be the right length and shape, so baring any crazy misfortune I think my problem is solved on that front, and when I get a couple of minutes I'll start putting that 261 together but I gotta drill my 848 head and get the springs swapped out for my patricks comp springs, maybe I'll port and polish it at the local shop, a guy there says he'll do it for 250 bucks and back cut the valves, and I think 20 extra HP? would be nice, that sound about right, 20?

dbane261,

I believe that you have studied the May 1955 HRM article about Frank McGurk's 261. Looking at the dyno test results from McGurk's 261 in 1955, the combined effect of increasing compression ratio from 6.75 to 7.85 and porting was to increase HP by about 2% at 2000 rpm, 7% at 4000 rpm, and 16% at 5000 rpm. The textbook equations indicate that the compression ratio change alone should increase HP by about 4% at all speeds. This would then say that the porting reduced HP by 2% at 2000 rpm, broke even at 2300 rpm, increased HP by 3% at 4000 rpm, and at 5000 rpm (if one wants to go there) there would be a 12% increase in HP. Are these changes worth it for a daily driver? Will a more modern approach to porting show better results? Let us know the results of your build.

Good to hear that your potential oil pump problems may be solved. Best wishes for your endeavor.

ugh that doesnt sound promising at all when you look at it in that light in comparison when you figure in the block mods, maybe I should just open up the bowls a bit and smooth out any rough castings, I am actually just looking to open up the intake ports actually, but yeah I guess I'll have to think about it a bit.

I get about the same: 5% for CR increase (solving for efficiency: E = 1-(CR^(K-1)) where K = 1.4).
The valve sizes are already about optimum (1-7/8", 1-1/2", yes?) but opening up the throat is far more delicate than just cutting. It must be done with a piloted ream or stone, and the area just below the seat ID is critical.
The single most important piece of machine work to an old head (aside from the valve job itself) is probably the top relief cut, which should be 15° and just intersect the new seat OD. The seat must be open to the chamber immediately on lift.
Round off the top edge of the exhaust valve where the margin reaches the chamber side. The intake should be left sharp here, just 1/64" radius. Back-cut = yes.
Manifold ports: don't enlarge the exhaust more than the manifolds, and don't blend or radius the transition - leave the edge sharp.
The intake can go up to 1-9/16, but don't go all the way in.

you can take the intake runners up to 1 9/16 huh? I thought you could push those things out to like 1 5/8? so backcutting would be a good idea then huh. Should I silicone the the pipe fittings on my oil screen where it connects to the pump and where the tube goes from the pump to the block? or use some form is a teflon tape perhapes? just to make sure that everything seals up, or should I just connect them and go?

Well.... 1-9/16" is the most conservative opinion I've found.
Some suggest 1-19/32", some 1-5/8", but all caution that this may not be true for all castings not only by part number but by individual core position, rust in the water jacket, etc.
By back-cut I mean remove material from the stem side by the shallowest possible angle to just intersect the inner edge of the seat and the stem radius - it must not leave any cut, ring, mark, groove etc. at the radius or the head will snap off.
I have never used a sealer when assembling pump parts, partially because it's never been a problem, but also because I have bad feelings about the long-term effects of hot oil on silicone and teflon. If I think they're not air-tight (remember, no pressure, only vacuum) I solder them together to keep the heat down.
If you start it and have no or very low pressure, a leak is a possible reason since the pump would rather draw air from a leak than viscose cold oil. Easy test for a leak between the pick-up and the pipe: add 2 quarts of oil to submerge the joint. If it's better, it was leaking. Unfortunately, the pump body is high enough that I'm not sure this method will work.

ok so the oil pump issue makes sense then, not to mention that I forgot that I saw like no sealants of any kind on the threads when I pulled it off, so thats a done deal now at least, So now I just gotta lube this mother up and get the pan and block painted before I seal it up and get the timing cover on. Oh hey this is a hair off topic, but is there any way to advance the cam/crank timing without the use of a crank gear with multiple keyways? like is it doable with the stock type gears? I am using an aluminum aftermarket cam gear and not the fiber type, so I guess the head work my just be on the outs as it does not sound in the end like its worth the money and the trouble for what its gonna give out in return.

any way to advance the cam/crank timing without the use of a crank gear with multiple keyways? like is it doable with the stock type gears?

The number of teeth make it impossible to make anything like a fine adjustment by just re-setting the tooth position. Each tooth is 13.33° - if it's that far off there's something wrong.
However, an offset key in either gear will make a small enough change to be useful.

dbane261, panic,

jimmy6 posted this thread about offset keys a couple of years ago. Call Cloyes.

I have seen some dyno data and charts in textbooks that indicate that most engines realize about 90 to 95% of the potential gain due to increasing compression ratio. I was trying to make McGurk's porting look as good as possible. If 5% of the gain came from CR, the porting that was done in 1955 would be even less effective than I calculated above. I am anxious to see what the CNCdude does with his head. I've believed that the biggest problem with the 235-261 intake ports is the sharp radius on the inside of the first turn, and it is not easy to increase that radius.

That's the big problem - very sensitive area, and no metal to play with, especially if the port is enlarged symmetrically (same amount at all points of the ID).
I'd like to see some results on a bench from only raising the roof, widening the intake but leaving the floor alone. This lets you do whatever is possible to the SSR, and also moves the active flow higher.
I have a gut feeling that the final throat enlargement might be better if done by hand for the last 1/2" in the arc tangential to the port and blend the throat into the SSR as much as possible.

so basically unless I get real creative with the runner, I guess I'd better not mess with it, I remember when I worked in an engine shop, old Fred used to say that most gain in the "porting" process would be gained in opening up above the valve and seat a widen it up, and smooth it out and work the bowls and throats out, should I have zero decked the head? If anyone has the software, could they tell me what CR I will have with a 261 block that has had 20 or 30 thousanths taken off the block, and I think its pretty much a stock 848 head, and flat top pistons? is there anyway to check and see/measure the thickness of this head? the shop that rebuilt it seemed convinced it would be around 9:1, but the pistons are nowhere near the top of the cylinder when they stoke all the way up. So stock 848 head, block with 20 to 30 thousanths off, and a standard head gasket, non coppper/non retorque type that is mesh and metal on the edges, thanks in advance people.

do you guys know of anyone who sells the crank gear that's advancable so I can advance the cam/crank timing? I don't need a full set, I already have a new aluminum cam gear so I would just need the advancable crank gear with multiple key ways

the pistons are nowhere near the top of the cylinder

That's not good - these engines were all built with quench, and in fact the chamber surface contains flow direction channels which are completely removed by milling (although Frohmader discusses restoring them in the Webrodder article, he's the only one TIKO).
#1: get an actual deck clearance measurement before you do anything else.

I will go out and try and get a measyurement today, but I am pretty sure that they are just standard height for the most part for a rebuilt motor ya know, should it be close to a zero deck, or like 15-20 thousands down just to allow for a little "stretch" when things get hot?

never mind, big time false alarm, that just must have been in the crank rotation when I saw then last, I hand rolled it over and they are pretty dang smack dab toward the top of the cylinder, I couldn't even get a 1/32 of an inch probably, maybe a little less than that, 1/32 of an inch is 31.25 thousandths from the deck, so if its a hair bit less than that it must be in the 20-30 thousandths-ish probably below the deck, is this suitable? and with an 848 head and standard head gasket get me the 9:1 CR that the shop guy was quoting me? Thanks in advance gentlemen, but the Kool April Nights Parade in Redding, Ca is tonight and I am gonna go watch a couple thousand hot rods run around and rev up their engines, see on here later.

Deck clearance + gasket thickness should be .050" or less, .040" is better.

so with the thickness that you stated, .050 and .040, with my 848 head and a bored out .060 261 motor, this would give a ballpark Compression ratio of about...?

Has the 848 head ben milled at any time in its history? Has it been cc-ed? I've heard conflicting reports on just what the combustion chamber volume is of an 848 or an 850 head. Once you know the combustion chamber volume, deck clearance, cylinder bore, crankshaft stroke, and head gasket thickness, it is fairly easy to calculate the CR, by hand or with one of the many calculators out on the internet.

so anyway thanks for the info, is there anyway to tell if the head has been milled in the past by eyeballing it? I heard once that there was a tab on the corner that is visible and it its looks like the number? is or something is not visible really good then it has been milled, also does anyone know where I can get a crankshaft advanceable gear, but just the crank part and not the cam part?

No one makes an adjustable timing set that I am aware of, the offset key will be your most likely option to use. Mr. Gasket makes an offset keyway pack that can be used on most engines that use this method. You can explore their website, and see if the ones they offer use the same size keys as the 235/261 engine. If so, then thats all you need. Just put a degree wheel on the engine first to verify where the cam timing is to begin with, and then verify after you install the keyway to make sure you went the right direction. I have a degree wheel already mounted to a solid hub that will work for these engines, so let me know if you need to borrow one....

I did find that key that they sell, and hopefully they fit our motors, and they are only a couple bucks, seems like a pretty good deal, so they come in like 2 and 4 degree advances, this was put together by a shop and put dead on, can I just paint a tooth and its corresponding joint between a cam and crank gear interface to find a reference point where it was, then pull off the gear, pull out the old key, push in the new one and then just slide the gear back where they were and adjust slightly for the advance? and would a 4 degree advance make my intake valve smack my piston?

I read that the keys are the same thickness. However: it's very important that the key bottom out in both the shaft and the gear. If you're not sure this is happening, take a light cut off the offending surface.

Like I mentioned previously, you need to check the cam timing first to even know where it stands to begin with. With all the machining tolerances in the timing set the keyway locations in both the cam and crank, it is doubtful that with the dots lined up on the gears that you are exactly at either 0 advance or retard with the cam spec sheet, if you have one. Its kinda' like just sticking your distributor in the engine, and turning it clockwise or counter clockwise until the engine starts. But until you put a timing light on it, you dont know if you need to advance or retard the timing. Also, you will need to check your P/V clearance as well to establish if you have or dont have adequate room to make changes in your cam timing to begin with. Advancing the cam makes you lose intake valve clearance, and retarding it makes you lose exhaust clearance. If the head is installed and torqued on the engine, you will need a dial indicator to check your P/V, if its not installed yet, you can use the clay method to help determine it, if your not that familiar with the process. Also, most people assume that TDC is the point at which the valves are closest to the pistons, and it is not, thats why a degree wheel is almost a necessity to do this correctly....

One of my concerns about pressing the same gear on and off a cam is that it could loosen up and allow the cam to side back once in use. I have seen it happen before. You may want to drill and tap the end of the camshaft for a bolt and washer just for CYA...

maybe I should just have a shop do this, has anyone else advanced their cams at all on this motor? were the results desirable? as far as I was told, for every 1 degree advanced, it shifts your RPM power band ahead by 100 rpm, so if your power band is 1200-4200, and you advance it 4 degrees, your new power band would be 800-3800, as far as I was told anyhow, so let me know if any of ya all have done this and what the results were.

If your engine is mostly stock, the cost of having to pay someone to do it will probably not be too cost effective for the results. If it is a pretty hot engine, then it might outweight the cost and be a lot more beneficial for you to do....

well it's looking like my plan to put this all back together is going to be waylaid for the next 4 weeks or so, finals are coming and I am so ready to be done with 19 unites worth of class, its pretty much rippin me a new one, but what can I do, if I work on the motor and truck, I won't get anything done for classes with my homework projects and all, if I get all my school stuff done-nothing gets done on the truck, so it is looking like it will most likely be an early summer project once school is over, gives me time to have the machine shop do all the cylinder head work for me and get simple things done like paint the block and pan and all and finish the block maybe. I just got done spraying oven cleaner on my fire wall and bellhousing to see if it will strip the paint, someone told me it will, we'll see what happens, any of you guys ever heard of this before? or know of an easy way to strip paint other than sand blasting or sanding?

You can brush this stuff on, stick plastic to it, and the next day what doesn't fall off can be removed with a pressure washer. Unbelievably easy but not real cheap.

http://www.new.cpfaruba.com/PDFs/English/Devoe/Hydrostrip%20502.pdf

Hey Scott,

When is the show and tell on a cut up 848 head?