Update on 216 to 261 engine switch

[Phil Waterman]

Up date on earlier, thread concerning setting up 261 engine to go into BEAUTY my C60S.
Old threads http://www.mapleleafup.org/forums/se...der=descending

BEAUTY has been re-christened Exxon-Valdez oil leakage has suddenly jumped to 3 quarts per 150 miles, so it is time to do something. First step was to get the 261 out of the donor hulk http://www.mapleleafup.org/forums/at...=&postid=45453 which was the truck on the left believe it or not. Turns out I’ve found another engine with no serial number so it looks like it was a replacement engine, the transmission was trash but once cleaned up the engine looks really good. Preasure checked the water jacket to 30 psi held pressure over night so don’t think I have any cracks in the water jacket. Cylinder bore measures within .005 of the nominal 3.75 bore. It will need one exhaust seat resurface for rust damage; probably will replace all the exhaust valves on principal. Crank and rod bearings all look good. It has the front engine foot for the center engine mount.

Now to my question what problems have people run into putting the 235-261 into CMPs. I’ve reread all the related threads shown above. If my information on the 261 one are correct is should give nearly twice the horsepower and 1000 rpm more useable engine revs.

[Paul Singleton]

Hi Phil,

Looking at your picture I see that your 261 has a FULL FLOW oil filter not a bypass filter like a 216 or 235. You can't remove the filter and plug the holes in the block or you will have no oil pressure!
Paul

[Bob Carriere]

Hi Phil

That is a good find...... you may be able just to deglaze the bore and use as is...... get the head done right if you want to get the most out the 261 inches. what is the serial number on the head.... should be cast raised near the manifold..... if it end in XXXX848 you have an even better head... if not check the other engine....... 848 will gove you slightly better compression and breathing..... usually found on 235 but you have to remember to drill the steam holes in the head to match the hole in the 261 block..... use the had gasket has a template.

You will need to replace those old oil part metal part rubber lines..... do not be tempted to use rubber lines dirtectly out of the block.... they come so close to the exhaust pipe they willnot last and probably pop catastrophically while the engine is hot and at high speed. Best bet to replace is to save the metal part and visit a friendly farm dealer who will make you the rubber sections to your requirements.

I intend to use the old hot rodder twin Fram PH 8 spin on filter bracket mounted insisde the frame and hidden by an OD painted sheet metal shield. Easy to service, no need to bath yourself in hot engine oil everytime you change them and they are $3.95 each at any auto parts store.

THe caution about the FULLFLOW is very appropriate.... it would be so easy to instal two pipe plugs to see if it will run..... deadly.

The big question is ..... how will the 261 water pump fit lenght wise...... you can save an inch by pushing the fan blade flange deeper on the shaft then cutting the shaft..... leave enough shaft to help locate the fan blade. Do you have the 261 5 blade fan..?

Do you have the carb..... need a big one for the 261 to breathe effectively....

Remember..... if you intend to increase the compression, you need to lower the deck height of the block as only a bare minimum can be shaved form the heads....

Keep me posted as my engine has yet to sit in the cab 11 frame....

Bob

[Phil Waterman]

Thanks Guys

Your tips and caution are appreciated. I probably will go with a new oil filter unit need to look for one with the flow rating, will need to relocate the oil filter unit either to the frame or up high on the manifold like the later CMP filter units. I’ll post some more pictures of this engine to my web page I’ve completely disassembled the engine now, to get the old oil that has gone gummy out of all the bearing surfaces and oil passages. Bob the block casting number is 376925 which from info I have means 59-62 the head casting number is 3835913. There is no stamped serial number on the flat behind the distributor, the hidden serial number behind the edge of the side valve cover is 035S.

Given the condition of the valve seats and valves I think I’ll take your advice and have the head done at the machine shop, replace all the valves. Before that though need to mic all the bearings only what to do this once per engine.

[Alex Blair (RIP)]

Originally posted by Phil Waterman
Thanks Guys


Given the condition of the valve seats and valves I think I’ll take your advice and have the head done at the machine shop, replace all the valves. Before that though need to mic all the bearings only what to do this once per engine.

A wise move Phil..You will find any cracks and get a good head,once in a life time job..The bearing caps could be removed and the bearing to crank clearances checked with plastigage..
Here is a good link to read before you start and print out to keep handy..I know it is about Fords but it is a handy page none the less..

http://www.fast351.com/enginerebuild/index.htm

Pay close attention for the use of plastigage on page 4...

Keep us updated..
The last 261 I had was in my '56 pontiac,before I switched it out for a 265V8 with a 3/4 race Duntov cam...

I know you know what you are doing but even the guy that wrote the article claims he could rebuild his engine with his eyes closed likes to have his favourite rebuild book with him whan he is working..

[Phil Waterman]

Thanks for the link - had problems getting in so people should try http://www.fast351.com/enginerebuild which worked a little better.

Who ever did this site spent a lot of time on it seems quite detailed. Interesting pictures and details

Been searching on line this evening and found a couple of other resources http://www.chevytrucks.org/tech/engine1.htm a 6 part on stove-bolt six engine swap and rebuild, little generic but helpful.

Reviewing systematic articles are helpful know matter how many engines you've rebuilt in the past, gets your thinking back in order.

[Bob Carriere]

Phil

When considering the location for the oil filters.... think of.....

a higher location may.... over a long period of sitting cause the oil to syphon back....

..a higher location as per the original location will encounter more heat from the engine and less air flow than lower in the frame....

.... less messy to service....

... on the plus side..... the higher location was adopted over the early lower frame location (see cab 11/12 service bulleting) to capture the engine heat and prevent water condensation the the filter...

Personally I am more concerned with potential cooling in the frame location.

Remote cast aluminium double spin on filters are avaialble from Fram for hot rodders and racers.... paid $20 for mine at a flea market.... with new filters.

There is / was an aluminium sleeve witih fins all around that used to be sold as an afetr market device.... almost like a radiator heat sink...... would slip over the PH 8 filters and held in place by one cap screw to tighten the sleeve around the filter.

Can seem to find them anymore... may have to search old Ebay again.

Before you spend to much time on the original 261 head check the other engine you have to see if you do not have the more desireable XXX848 head.

When rebuilding ......caution... the complete rocker arms assembly are getting very hard to find..... and remember the 235 and 261 assembly are interchangeable.......

I have a 1959 GM shop manual .... which I can reference or scan the engine section for you.....

The good thing about you working on the 261..... is that at the speed you work...... you will have ironned out all the kinks for fitting the engine in the CMP before I get to that step with mine..... for this I am eternally thankful........ hahaha

What will you use for carb...??? mighe be able to help you out..

Bob

[mike mckinley]

phil and bob


it's funny how things work out, all three of us have 11/12 cab trucks, which are now( or soon to be) sporting 261cid engines. as for carbs, the manifold on mine currently holds up the remnants of one very worn out rochester. mike

[Bob Carriere]

Haven't heard from you in ages Mike.....

Like I said ......let Phil do it first..... he is very thorough and will solve all your headaches......

How far are you into the cab 11.. I thought you had Iltis-situs....

Suitable carbs of the late 50 era are still coming up in EBay once in a while...... carb core are available at $10 and up....Rochester carb kits anywhere from $15 to $25..... have to be careful... some models have a flat shaft to the accelarator pump ... some have a round shaft......you have to take apart you carb first to see what you need.

Some mechanics hate Rochester B carbs with a passion.... prone to leaking at the top cover and to warping of top cover..... a good source of info is the Stovebolt site.....other aftermarket carbs will fit but you have to match the CFM and torque curve response.... and the concern with appearance and airfilter canister requriement.

I found an NOS 261 Rochester B carb circa 1960 for my engine in California on Ebay.

Hang in there.

Bob

[Grant Bowker]

As recently as 2002, J C Whitney was selling a "Cooler Collar" that was a finned sheet to wrap around oil filters that was supposed to be two sizes fit all, held in place by band clamp. They might still sell them, worth trying if you want the device.

[Phil Waterman]

Currently there are a number of 261 parts including an intake exhaust air cleaner and carb on e-bay which I don’t plan to bid on http://cgi.ebay.com/ebaymotors/ws/eB...0389714&rd=1,1 I’m trying to track down the numbers on the actual 261 carburetor according to some of my reading it was different than the 235 but that many if not most 261 engines have over the years ended up with the down sized 235 which would be dropping the fuel air flow.

The 261 engine is completely cleaned, disassembled and I’ve mic all the bearings everything was looking like I could just replace the valves have the head done and replace the rings. That is until I pulled the # 4 piston and discovered that the bore and piston are scored this is the same cylinder that had the worst valve, real shame because the bores all measure up as being good. For now all the parts are boxed and up on shelves in the barn loft.

Bob will take your advice on the cylinder head and check the one on the other engine. Was planning to pull the engine up of the other donor truck anyway before snow flies, don’t want to have to plow snow around it all winter. Plan to move it into the shop today so we’ll see what kind of condition it is in.

[Alex Blair (RIP)]

Originally posted by Phil Waterman
That is until I pulled the # 4 piston and discovered that the bore and piston are scored this is the same cylinder that had the worst valve, real shame because the bores all measure up as being good.

Phil..
How bad is the #4 cylinder...Will it rebore ??

You are then it some serious money with pistons and all the rest ...Oh well if you have another ,that is the cheeper fix..
HERE IS SOME GOOD CARBURATOR INFO ON SIZING......
PRINT IT OFF AND KEEP IT..

Air-flow capacity: It is important to correctly size the carburetor to the engine's operating air-flow requirements. Too small a carburetor limits horsepower; up to some specific speed, normal torque is obtained. Beyond that point air-flow is limited by the carburetor and power drops off.

A too-large carburetor will cause starting troubles (too low vacuum signal at cranking), idle will be hard or impossible to set, and fuel/air mixture will be incorrect.

However, type of service also has a bearing on carburetor sizing; an engine that is never operated at full-load conditions is sometimes better off with a slightly-small carburetor; it will have improved low-end torque and easier starting. Passenger cars, forklifts, etc are good examples. Engines operated at or near full load, such as stationary engines, generators and the like, may produce better power with a slightly oversized carburetor.

Determining engine air-flow from the charts: The chart below gives air-flow requirements for most engine sizes. Use the next-closest value. Engine RPM should be the highest speed during actual use, such as accelerating under full load at highway speeds. Use the carburetor chart to pick the appropriately sized carburetor.

Calculating exact engine air-flow: You can easily calculate the actual engine air-flow directly. For normally-aspirated engines (ie. not turbo- or super-charged):

CID * RPM / 3456 * 0.85 = CFM required
CID is engine size, in cubic inches (CID = cubic centimeters (cc) * 0.06102), RPM is maximum engine speed. 0.85 is a close approximation of Volumetric Efficiency.

For turbocharged or supercharged engines:

CID * RPM / 3456 * %boost + 1.00 = CFM required
Normal inlet air pressure is 14.7PSI; supercharging merely increases inlet pressure. For example, 6PSI boost means 20.7PSI pressure, or 140% boost.

IMPCO Carburetor models vs. air flow
Vehicle applications


IMPCO Max.
Model CFM
50 91
50-500 108
100 170
125 202
175 210
200 276
225 329
300A-1, -20 348
300A-50, -70 432
425 460

Industrial/stationary applications

IMPCO Max.
Model CFM
50 118
50-500 124
100 197
125 235
200 345
225 380
200D 468
425 533
200T 680
600D 1600

Engine size and speed vs. air flow
NOTES: These tables assume 85% VE as mentioned in the text. To convert liters to cubic inches, multiply by 61.02. For two-cycle engines, double the CFM value found.

Engine speed, RPM 400 - 2400 RPM
CID 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
50 5 7 10 12 15 17 20 22 25 27 30
100 10 14 18 23 28 33 37 42 46 51 56
150 14 21 28 35 42 49 56 63 70 77 84
200 19 28 37 46 56 65 74 84 93 102 110
250 23 35 47 58 70 78 93 105 116 128 139
300 28 42 56 70 84 98 112 126 140 154 168
350 32 49 65 81 98 114 130 146 162 178 195
400 37 56 74 93 111 130 148 167 185 204 223
450 42 63 83 109 129 149 169 189 209 230 251

Engine speed, RPM 2600 - 4000 RPM
CID 2600 2800 3000 3200 3400 3600 3800 4000
50 32 34 37 39 42 44 47 49
100 60 65 70 75 79 84 88 93
150 91 98 104 112 118 125 132 139
200 121 130 139 148 158 167 177 185
250 151 163 174 186 198 209 220 232
300 182 196 208 224 236 250 264 278
350 212 228 244 260 276 293 309 325
400 242 261 280 298 317 335 254 372
450 272 293 314 335 357 378 399 419


Phil..
You might also want to take a boo at this link..I found it interesting..

http://www.oldchevytrucks.com/Tips/261_six.htm

[Bob Carriere]

Hi Phil

Will check the 1959 GM shop manual for the exact carb number for the carburator..... also have the parts number manual.

I have also collected a number of Rochester manuals and spec sheets over the years that I can share with you.

On Stovebolt...links to CARB KING...... extremely helpful gentlemen and has all the carb kits required.

Will also send you the carb throat size and bolt pattern that ID a 235 from a 261 carb.

Hope that cylinder can be bored out to save the block.

The engine you took out..... did it have the truck solid lifters???
.... have you considered installing a two stage fuel/vacuum pump to help out with the wipers..??

What are you planning with the exhaust....stock or split manifold.

Did it have a metal PCV valve installed on the breather tube???

So many questions... so little time.

Kevin from Lebanon is coming up Nov 4/5...... is there anything you need I can give him to ferry to NH ...??

Bob C.

[Phil Waterman]

First thanks Guys for the feed back and suggestions

Yes, I am pretty sure that the block can be bored to take out the scrapes. The rocker arms show more wear than anything which makes me suspect that is a engine is a short block replacement which reused an earlier head. Engine was definitely a transplant in to the truck I found it in . Think I’ll be able to use the exhaust manifold at least for test purpose may switch over to the spit exhaust manifold. I’ll post some more pictures to my web site this weekend details on the 261 engine.

Can’t think of anything I need shipped south right now Bob.

Can’t leave truck alone in the yard strange things happen. Actually was moving the other donor truck into the shop to remove the engine.

[Bob Carriere]

Geez for a minute I thought you were breeding the little suckers...

Mechanical husbandery..????

Back to the real world...

My 1958 GM truck manual says the carb should be 7005140

for the 235 for the 261
7004468 7005140

Throttle bore 1 9/16 1 11/16
Main Venturi 1 11/32 1 15/32


The above carb part numbers checks out against the parts GM manual for 1958-59-60. Carb kit for the 261 is 7006126....

Will need to measure up a real carb for the bolt pattern spread but the 261 carb is just big enough it will not bolt on a 235 manifold and vice versa.

Both the 235 and the 261 are referred to as the Rochester "B" type.

There are some after market circa 1959 Zenith and Carter Y that was used on these engines and somewhat preferred by certain mechanics.

Keep us posted of developments.

Bob

[Bob Carriere]

Nice listing of 261 carb parts on Ebay...... shipping to NY is about $50 and that kills it.

Last time at Barrie I picked up a similar set up... with horn mounted on manifold for $25........ carrying to the parking lot was a $50 dollar pain...... it was not has cleaned and messy to craddle in your arms.... proved to be a good donor of parts.

Bob

[Barry Churcher]

Guys, don't spend too much on these Rochester carbs. Brian Gough and I passed the $15.00 ones by at Hershey because there were lots there cheaper. Look for the ones with the manual choke brackets still in place. These carbs are really trouble free and in 40 years of working on them I have never had a problem that wasn't easily fixed. Usually it was my fault anyway!
Kits are about 15 to 20 bucks, Just make sure the passages are clean. To obtain proper performance you should use the proper size carb on the 261. Also it is better to use the exhaust manifold also, even though most most of them exit at an angle and you need a bigger exhaust pipe. You probably need the pipe made up anyway. Also make sure the heat riser functions. When we used to have a lot of these engines coming in for tune ups we always checked the manifold to head nuts and gave each one a little tweak.
Cheers,
Barry

[Phil Waterman]

Hi All

Well I now have two completely rebuilt engines to go into my 3 Ton CMPs.

I've got the 235 up and running on the test stand see http://www.canadianmilitarypattern.c...ineTesting.htm bottom of the page for some photos and of course video of the new engine running. Still breaking, I mean running the 235 engine in couple of minor little things to fix like one noisy exhaust valve rotator.

One point of interest from running on test stand the T that connects the oil filter line and oil pressure line to the block broke the other day, so much for reusing 50 year old brass parts, fortunately I was standing at the control panel and saw this straight black line appear between the side of the block and the wall about 10 feet away. In the short time to realize what was happening it pumped 2 quarts out of the engine.

[Mike Timoshyk]

I just have to comment on the quality of websites offered by patrons of this website.

I visited in succession Phil Waterman's, Keith Web's and Hanno Spolestra's sites. All I can say is Bravo Zulu...

I am sure it has been mentioned before but, I just wanted to pass on my appreciation.

Cheers

Mike Timoshyk in Sunny Windsor Ontario...still cold, but sunny.

[Phil Waterman]

Hi All

Been working on the 261 engine which has the large full flow oil filter, while the 235 is running on the test stand to warm the shop.

In the picture at the top of this tread you can see the original full flow oil filter unit as used on the later 261 chevy truck engine. As I'm preparing the engine to start running it in I was working on the oil filter unit, comparing the original with the replacement spin-on type filter unit I plan to use. Couple of things I noticed one the original has a bypass valve if the the filter becomes plugged. It would seem a good idea as the new spin-on filter unit doesn't have this feature. So figured I'd find out at what point does the bypass open and discovered that basically always flowing oil and never really closing completely. With this in mind I guess the spin-on with no bypass is a more positive way of filtering the oil. It also means that if any of you are going to reused the original 261 filter units be sure to clean and check the filter bypass.

As to the 235 on the test stand this particular engine has the hydraulic valve lifters and valve rotators on the exhaust valves. While the engine sounds pretty good and getting better all the time, when you let the engine sit for a couple of days and the lifters all have a chance to leak-down all the way it sounds like a cement mixer full of rocks when you first start it until the oil pressure comes back up.

[Bob Carriere]

Hi Phil

That can't be right....... lifters should not leak down that easy or that fast..... unless the oil pressrue is tooo slow building up on start up.

My experience with Chev 6 goes back to the fifties.... all on 235 in cars with hydraulic lifters..... and even after parking the 58 chev for the Winter.... it never made a racket when staretd in the Spring... it might some a little from the oil in the cylinders but never noisy....... you might hear a clacking of valves for a few seconds.......but never more than that.....

Are you sure you didn't rebuild a diesel......????

Barry "Cherchez la femme" might have more practical experience with them...

Must be a lot of others running 235 with long shut down......

BooB

[Phil Waterman]

Hi Bob

Well maybe cement mixer is a little harsh, maybe a sewing machine, but with the engine sitting out in the open with no fan it sounds loud (fan is electric on the test stand right now). Just after letting the engine sit for 3 or 4 days the first time I started the engine the top end sounded like a 216 with really loose valves adjusters. Of course once the engine built oil pressure (you right a couple of seconds) the noise went away.

The leak down may have been helped by the fact that I'd left the block heater turned on so the engine sat over the weekend at 100 F which would have kept the oil thin. I'll repeat the experiment and see if it happens again.

The oil pressure cold or hot is holding very steady at just about 40 psi regardless of engine speed. With the engine run in a little now I can let it idle down to under 400 rpm with no problem, still limiting top rpm to 1500 and not for any length of time. When I'm running the engine I keep changing the rpm up and down every minute or so.

Cheers Phil