m135 underpowered

[jb31]

ok i have a m135 that i use for plowing snow and fire wood. i love the truck it has the stock 302 but with a 5speed stick behind it. it is way underpowerd due to age and lack of the low range in stock trans. the moter was stuck when i pulled the truck from the woods but it now runs petty good starts up even when 10 below. i really want to update the motor, has anyone put the effort in thses old trucks with success. i had ideas of an old 2 stoke detroit or cummins or possibly sbc. like i said my son and i love the truck just want to get more out of it without spending a tone. thanks

 

[Westech]

you can make that 302 push 225 HP very ez. Take the head off have it shaved as much as they can do safe, replace the carb with a 2GE Rochester and have a 2.5 inch exhaust and good muffler. Push the timing to 8-10* BTDC and away you go. Thats it.

 

[jb31]

that has crossed my mind, i was thinking bout goen somewhat modern with it, the 302 is a great motor and they say the racers still like them, but it needs new exhaust manifols, and a whole list of other patrs to make it where i want it. just had the idea of maybe a 7.3 diesel or cummins. just depends on what i find at the right price. this will be a summer time project for my son and i

 

[emr]

Will the trans explode after the rebuild? maybe pick a motor that has an easy awesome trans option for later use,

 

[jb31]

the trans is i believe out of an older dump truck not the orginal auto, probly had a 366 in front of it at one time, i had figured in a complete swap if i did do it. my idea was to pick up a motor trans combo from a local yard that was from a rusted out truck, we tend to have alot of those around here. i just wanted to hear if anyone had done it before with this truck. the m35 seems to be the common one now and this 135 is long forgotton

 

[topo]

jb31 you might try Boyce Equipment 1 800 748-4269 at one time I think they could make the m135 transfer case a two speed

 

[emr]

sweet god luck..

 

[JasonS]

you can make that 302 push 225 HP very ez. Take the head off have it shaved as much as they can do safe, replace the carb with a 2GE Rochester and have a 2.5 inch exhaust and good muffler. Push the timing to 8-10* BTDC and away you go. Thats it.

You can shave the head 0.0625 and get 7.7:1 or .125" and get 8.3:1 compression ratio. If you do this you will need to mod your side covers and put spacers under the rocker arm assembly. It is really not the proper way to increase the compression ratio. I'm not sure that you'd notice the diference at the relatively low speeds that this engine spins anyway. The folks that I have talked to who have done a complete build up for HP expect 230HP at 4500rpm. Increasing the engine speed with the stock heavy pistons wasn't recommended.

The way to get a two speed transfer case is to use one from a CCKW.

 

[JasonS]

That person spent $3500 on parts and machining and did the assembly himself. It is very expensive to get HP from a 302.

 

[jb31]

im not really interested in putting the money into maken the 302 fresh again, but changen the case is a good idea, i may have one from a m35 out back . i had planed on putten a small dump bed on it this summer and changen to a snowblower on the front with a pony motor to run it and i just wanted something newer and more powerfull under the hood. has anyone tried a 7.3ford motor in one of these,

 

[wreckerman893]

that has crossed my mind, i was thinking bout goen somewhat modern with it, the 302 is a great motor and they say the racers still like them, but it needs new exhaust manifols, and a whole list of other patrs to make it where i want it. just had the idea of maybe a 7.3 diesel or cummins. just depends on what i find at the right price. this will be a summer time project for my son and i

There used to be a lot of aftermarket speed parts for the 302 six banger...try doing a Google and see.

I think I remember there being headers, custom intakes for larger carbs, cam kits, etc. available through some speed shops.

At one time the 302 was a very popular hot rod and racing engine.

 

[rosco]

Long ago, I put a 5 speed in a 211 (don't forget the clutch), & the T-case from a CCKW. It was a lot of work. The T-case is marginal for the stock power of the 302. I blew it. Its smaller. Think about all the work. When done, you'll still have a gasser that is modified/some would say cobbled! When I did all that work, the M35 was far beyond my reach. Today they are quite prevelant. The power train is far superior/stronger to the 211. I think that I would keep the 211 for play and get another truck truck for work. Good Luck

 

[JasonS]

Here are the notes that I saved from the engine build noted previousy in case someone else is interested in increasing the 302's HP:

302 GMC Buildup Notes​

OK, I'm no pro engine builder...... the head has Chevy small block V-8 valves,1.94 intake and 1.60 exhaust. They are Manley Street flow, 7 bucks each. The exhaust seats were replaced, the intakes opened up slightly, standard hot rod stuff, any decent machine shop can do the work. The springs are Crower singles with a damper, so called Z-28 springs. To get an installed spring height of 1.700,a set of Manley lower spring cups fit right in the stock valve spring recess in the head. The slightly shorter valve stems messed up the rocker arm geometry, simple fix on a GMC, just drive down the valve contact pads, weld them in the correct position.
I got a cam reground by Colt Cams in BC Canada to my own specs; they do excellent work. Delta cams in Washington can do it, as can Lazer Cams in Tenn. or just about any of 100's of cam grinders if you know what you want. The typical guys who have ready ground cams for these engines, Langdon, Clifford, Howard's, base their total valve lift on a rocker arm ratio of 1.5,but actually as measured, it's 1.4. So right off the shelf, you're loosing .020-.040 total lift and some duration.
I bought header flanges on Ebay, the guy has some Chevy 235 flanges advertised at the moment. The flange port openings were too large, probably for some wildly ported engine. It was a pain in the ass to weld in material, better to use 235 flanges and rework them to fit. Or just get a pattern from a stock manifold flange and have a fabrication shop do a set for you. At least the flanges are 3/8 stock and cheap at around 35 bucks. I got some 1-5/8 and 1-3/4 U bends from Summit racing, cut em up, welded it all together, a 10 inch steel cutoff saw blade on a chop saw or radial arm or table saw make it easy to do square cuts or angles. I made no effort to "tune" the individual pipes, as it doesn’t matter on a relatively low RPM STREET engine.
The 4 bbl intake came from Patrick's, 1/2 the bucks of Clifford, using a 390 Holley 4bbl for starters.
The oil pump pick up tube is fairly small on GMC's, a reworked larger diameter Chevy small block tube with a home made pick up looks better.
This engine wasn't cheap, I do my own assembly and design, but all the machine work, Venolia pistons, valve train, a million little this and that's has cost around 3500 bucks, ouch! Even the bearings were a fight, the only readily available mains are made in Mexico Federal Moguls, took some searching to find premium Clevite 77's. When I started building this engine, I got a lot of bogus information from vendors and guys who supposedly are GMC experts, like a GMC is some special magical engine.


I just completed a 302 as we speak. I used Chevy V-8 1.94 intakes and 1.60 exhaust valves, Manley hi po street valves, springs with a damper, again V-8 item. Comp Cams makes a lower spring cup that fits perfect and gives a 1.700 installed spring height, perfect. The small block valves have a slightly shorter stem; ya need to correct the rocker arm geometry, easy to do. I got a cam ground of my own specifications, I highly recommend Colt Cams in BC Canada. My cam is 215 degrees duration at .050 lift, lift at the valve is .430.Remember this, the actual GMC rocker arm ratio measured by me is 1.4 not 1.5 listed by all cam makers. So, all the cams you see are short on actual valve lift by about .035 and short on duration by a few degrees.
I'm running an actual 9.3 compression ratio, Venolia pistons; I sent them a mold of the combustion chamber to design the piston. Using 1/16 compression rings, 3/16 oil rings. I measured the stock 302 head combustion chambers at 121 cc's, had the head milled .040 to get the chambers to 112 cc's to keep a small 25 cc piston dome. The pistons are installed at zero deck clearance. The rod small ends were rebushed for Chevy big block V-8 wrist pins so I wouldn't have to have custom pins made.
I searched around quite awhile to find Clevite 77 bearings; the mains have been out of production for 20 years. I didn't want to use the currently available Federal Mogul made in Mexico bearings.
Got a 390 Holley 4 bbl on a Patrick's intake and a home made set of short tube tri-y headers.
I modified the oil pump pick up tube by using a larger diameter tube from a V-8 with a home made pick up enclosure and screen. And of course the full flow oil filter.

Should make 230 HP at 4500 rpm.



Jason, I may have overstated using "bogus", lol. Here's what I found, like I mentioned, the actual rocker arm ratio is 1.4 not 1.5, so keep that in mind when choosing a cam cause all the cam grinders think it's 1.5. I measured the lift at the lobe and at the valve with corrected rocker arm geometry. So I had a cam ground with more lobe lift to make up for it.
I also noticed the stock oil pick up tube is a smaller diameter than the pressure feed tube of the pump. Just about every other engine design has a larger pick up tube than the feed side of the oil pump. I modified a small block Chevy pick up tube, it's larger than the stock GMC item. The 90-degree fitting on the feed side of the pump is restrictive, I bored out the diameter as much as I dared, better yet would be to throw away the sharp 90 degree fitting, and use a larger radius fitting. Same goes for oil lines on a full flow filter, avoid any fittings with sharp turns. Each sharp angle fitting reduces oil pressure by a few psi, add em all up and you loose 10 psi. You can jack up the pump relief valve spring, but that just takes more power, and may overload the drive gear and heat up the oil.
Quality bearings were another problem; I searched quite a while to find genuine Clevite 77 main sets. The only readily available bearings are Federal Mogul CP's made in Mexico. They are supposed to be a good bearing, but I wasn't satisfied with the bearing crush, the Clevites were much better.
The factory machining on this standard bore block was horrible, the bores weren't straight, the block deck wasn't parallel to the crank, but the crank bores were right on. The machinist had to mill the block at a angle to get it straight. The bore problem was solved by properly boring the cylinders on true centers.
The Crankshaft was standard and smooth, but the throws were off and the factory had cut the crank slightly undersize. I didn't want to cut the crank at all cause you loose the hardening, but I compromised with a .010 cut, and trued up the crank throw indexing as much as possible. The connecting rod bores were off as much as .010. Took care of that by rebushing the small ends for 0.990 Chevy big block V-8 wrist pins, offsetting the bushing bores to get all the rods the same length.
I'm not vendor bashing here, but both Arias and Ross didn't seem interested in making me pistons. Venolia was interested and asked for a head combustion chamber mold so they could build a piston to fit my specs. And they were cheaper by 100 bucks.
All these little items do add up; makes no sense to throw money at a performance engine unless you check every item and correct any problems. I mocked up the block, crank, rods and pistons several times at the machine shop to check clearances along the way. My machinist is careful, but it's my engine, I do my own assembly, it pays to be involved during the machining process.
I did these steps on the 261 I built for the truck 7 years ago and it had excellent power and was smooth, hopefully the GMC will run as well and the 3500 bucks I spent for machining and parts will be worth it.

 

[jb31]

well i am on the hunt for a m35 but the 135 is what i have to work with at the moment, i realize alot of people say to keep it origanal but it was already modified when i got it. i can pick up a 7.3 with trans for 200 at the local u pull it yard and im not interested in droppen 3500 into the old 302, when i do the project the runnen 302 will probly go on here or ebay for someone who wants it. even for play the truck is way under powered i think even with its age, its still a great old truck. i do thank everyone for all the advice but im still on the hunt for someone who has done a newer motor conversion in this truck, preferably diesel.

 

[ALA2]

hello I know a guy whoput a 7.3 in a 715 nothing but trouble . engine is very large for alot of engine compartments.maby a inline 6 diesel'buy a old doge andhave all the parts u need.
dont know about 4x4 hookup.good luck sounds like a great project al.

 

[73m819]

why not put a chev 350 and the heavy duty 4spd that was in the early pu (70-72) or something like that. for that matter a chev 250 six and same trans as above would work good

 

[Tplane37]

On that 302, there is a lot you can do to get power out of it from the research I have done in the past week alone. ( I just bought a 52 Jimmy last night, bringing it home tomorrow). I got my first catalog in the mail today from Patrick's Antique Cars and Trucks (PATRICK'S ANTIQUE CARS AND TRUCKS). Headers for $260. 4 barrel aluminum intake with Holley adapter for the same price (this would allow a Holley Projection type set up to convert you to fuel injection). They have an intake that lets you run up to 5 of the Ford 3-bolt carbs (block off plates if you only want to run 2 or 3). They have heads, can custom grind your cam, they offer 29 ounce forged pistons (as opposed to the stock 43 ounce pistons). Oh, and they are willing to help you on your engine build.

A 4-71 blower works on the GMC 302 as well. This engine holds speed records on the salt flats upwards of 250 mph (in a Ford deuce coupe, not to be confused with a deuce and a half LOL). They say it is one of the few engines out there that lets you get 2HP per cubic inch with relative ease, and an increase in horsepower results in increased torque and fuel efficiency.

If you go with the diesel conversion, I'd choose the Cummins 6BT or CT over the 7.3 Powerstroke for simplicity. The older (read pre-1998.5) Cummins are all mechanical injection an require minimal rewiring to your truck. The 7.3, while more readily "tunable" once installed due to the availability of power programmers, etc., are going to have you ripping out any hair you have left during the retrofit. They have multiple computer systems that are constantly talking to each other and literally miles of wiring....stay away from the 6.0 Powerstroke at all costs. You're better off with a team of lame mules.

 

[Tplane37]

Double post.... moderator please remove.

Tplane37

 

[TURBO6X6]

Hi, I am a new member, not sure if your still looking at the mods for your truck. Anyway I have a 1955 M135, I got a 1991 GMC school bus with a 366BBC and an Allison 4spd automatic tranny. I transfered the engine, tranny, all the front end/dash wiring, power steering, power brake master cylinder, added propane tank and two turbo chargers. I now have about 450 lb-ft of torque and around 350 HP at 10lbs boost, according to turbo chart. I left the stock transferr case, and single speed also.. Anyway it works very well, i use it for hauling wood, water and landscaping stuff. I would like to convert the transferr case to a two speed but not sure how this is done. I have another same M135 and a 7.3lt powerstroke of which I want to install. The allison auto tranny and any engine will work, just would be nice to have low range in the tranfer case for those over weight had wood days...

 

[JasonS]

They say it is one of the few engines out there that lets you get 2HP per cubic inch with relative ease, and an increase in horsepower results in increased torque and fuel efficiency..

This is a 1930s technology engine. 2HP / cubic inch is very difficult and expensive. Anybody who says "it can be done with relative ease" is lying to you.