Inliners International Forums General Discussion Engines Where to find piston and rods for 270 GMC

This explains the GMC full flow conversion. It's also here on the Tech Tips page if the link doesn't work.


https://www.inliners.org/tech/full_flo_GMC.html

That link didn't work for me. Try this one. It is straight from the Tech Tips in the side bar at the left of this page. Good clear instructions use care and you'll be fine. It is simple.

Fill Flow

Wow that is pretty simple actually, should have been that way factory. Now I got to figure out what I want to do build wise with the engine Factory output is 130hp and 240TQ which is pretty decent actually, so im thinking stock cam and maybe bump up the compression a little?

Not hard at all. The ticket part is drilling the hole in a thin part of the block and being able to thread it.

A lot has been learned about cams since 1959. Check some of the milage grinds as they are perform in your normal driving range, off idle to 35000 or so. With a good mild build and the right gearing you'll be happy.

My cam looks pretty rough anyone who still makes cams for these? Called eggy they do not make pistons for 270's gonna have to go for ross or maybe some NOS

Finding a cam company that has cores to make a new cam for you may be tough, you'll just have to start calling A to Z to find one. If your old one still has good teeth for the distributor , you can always consider having it reground....there is also a bunch of GMC guys over on the HAMB and Stovebolt forums that might give you a better core if yours isn't salvageable.

Your old cam and lifters can be sent out for regrind. 12Bolt can help with this. There are many cam companies that still offer this service. Not all can do lifters.

Found some NOS zollner .40 over flat tops! paid up for em but hey they are hard to find and came with some good rods even.
Now to find some .40 over rings.

Does anyone know how to tell if a oil pump is good? I found a rebuild kit but am curious if it needs it or not.

You would have had to seen the engine in running condition to know for sure. If the gears look scared up and rough then its probably best to replace them. Since the condition is unknown, replace them to be on the safe side....

I�ll take it apart and tell you what I see with it, my next question is, is it worth mulling the head to up the compression? Not trying to build a race motor but want a good running engine I could take on the highway to 65 but mostly in town. Same with the cam selection don�t need nothing crazy but maybe a little hop up?

If it's not broke, don't fix it.

On the GMC, the top row of bolts for the side cover bolt into the cylinder head. The more you mill the block and/or head creates misalignment in the side cover. Easily fixed, just be aware it affects things the more you cut off....

Yeah no milling it is then, to keep the stock look and hop it up some a small cam, and 2bbl 302 intake and exhuast. I think factory it had 130hp and 250tq so not a slouch stock.

Better plan: tell people you have a cam, and don't.

If you are going to put a big port intake on a small port head there will be a sharp reduction in size at the head. Some fitting can be done but you may need a special gasket to seal it. I have that and you really have to pay attention. The GMC has 3 rings that help align the intake & head. I made a set that fits the big port on one side and the small port on the other. The ID is tapered to help reduce the restriction. I think it actually helps increase velocity.

I just want to make sure, that the linkage would be the same so I don�t have to mess with that. Should I try and find a 302 exhuast and intake so then I don�t need the adapted gasket or would you still need it.

It will be easy and straight forward if you just stick to your 270 parts. You do not need anything 302 and you will gain no drivability by using them. If you want more carbonation do it with a 270 manifold. There is power to be had with better intake & better exhaust but you can add that later if you want.

Yeah I probably should just leave it alone for a while.
Anyone know if someone makes a GMC engine paint?

So the rods I got with the pistons I bought are 2135419, the ones that came out of the engine were 2341204. Worried about them working with the crank now.

Double check the forging number on the one's that came out of you engine, there is a 2342204, but I don't see a 2341204. They only difference you'll need to worry about with the crank is to make sure you get the rod bearings with the correct tang to fit the rods properly.

I double checked casting number is 2341204

That could be a less common forging number then, but the bearing tang width and wrist pin size will dictate what parts are to be used.

Just got to the carburetor on the engine, it�s a carter YF which I believe is not factory and the throttle shaft seems to be broken off.

Pictures?

I can't really tell. I don't think it is stock. Over the years lots of carbs have been replaced with whatever would bolt on. It does look broken.

I did this simple search and you may find some info here. STOCK 270 Carb

Yep Not the correct carb, I might go raid a 270/302 GMC at the local junk yard to get the carb and the correct linkage.
Anyone know of a place that would be willing to make me some pistons rings if I can not find any for my .040 over pistons?

Keep looking on eBay rings show up.

There is a set of 0.050 over that could be sized of that fit your pistons.

Is that the CCKW ring set? I�m not sure if the earlier rings would fit, but I can�t imagine they would change it.

I am not an expert on rings & fitting rings. You should do some study before you jump into it. Here is a link to the 0.050 set I saw. Thee is al the so an expensive 0.040 set from Australia.

0.050 Rings

I found these not sure what .040 over is in fractions.
https://www.performancenowdirect.com/piston-ring-set-1956-62-gmc-truck-6-cyl-270/

That works out to 3.78125 or standard bore.

Well new problem, the bell housing is a Chevy bell housing, will that fit my 270 or will I have problems? Casting number 3837001im debating switching to a 4speed now.

If you can give them the dimensions, Total Seal can make you whatever ring you need! Good people and grat products!!

Update: Got to get a dimensions for total seal and they will make me some rings, block is getting line bored and should be done this week or next with the full flow conversion as well, I will be a 20 overs on rods and mains. Will be sending in the cam and lifters next. Now I am worried about the oil pump and if it works or not.

Be a good idea to still consider getting a 302 intake manifold. The reason Tom Langdon suggested it is because it takes a 2 barrel carburetor and you need a carburetor anyway. The larger carb will help performance, the manifold bolt pattern is common to the small Rochester and Carter bbd 2 barrels. I run one of these on my 270 I have in a 47 Chevy 2 ton:

https://www.ebay.com/itm/125234014726?hash=item1d28876a06:g:92gAAOSw2X5iRb4Z&amdata=enc%3AAQAHAAAAoOfoQnbwV7u0V%2BjrhYahTsyQePShI2qYmm%2FkPvKpsIQG2cGx3T0VFyVWHgasR8Nxn84yMtq%2BXwzpy4kIlLb%2BZV078wtKxnGYmW9TyToVeOA52I%2F%2F2YrfhD2ykBEmfrPVmM%2BKuMFaVQQjI6uKuDTQvuSRiQ1pPqvLgyOa%2FuSm%2BqhLU9PJB3upn7KN090CohDa3Uc%2FoY1G97wWx5jUDUym0yA%3D%7Ctkp%3ABk9SR8aj2_nfYA

https://www.ebay.com/itm/125234014726?hash=item1d28876a06:g:92gAAOSw2X5iRb4Z&amdata=enc%3AAQAHAAAAoOfoQnbwV7u0V%2BjrhYahTsyQePShI2qYmm%2FkPvKpsIQG2cGx3T0VFyVWHgasR8Nxn84yMtq%2BXwzpy4kIlLb%2BZV078wtKxnGYmW9TyToVeOA52I%2F%2F2YrfhD2ykBEmfrPVmM%2BKuMFaVQQjI6uKuDTQvuSRiQ1pPqvLgyOa%2FuSm%2BqhLU9PJB3upn7KN090CohDa3Uc%2FoY1G97wWx5jUDUym0yA%3D%7Ctkp%3ABk9SR8aj2_nfYA

Tom Langdon can help you find adapter rings to make the large port manifold fit the small port head.

Little update here, got busy machine shop was backed up thing came up, but I�m back at the rebuild now, turns out the rods are 302 rods that came out the 270, but I do have a set of good 2135419 rods just wondering if those will work my crank it says both the 302 rods and that casting number rods use narrow bearings so it should be alright?

I think you keep missing what is being said to describe the connecting rods. All GMC rods, regardless of what cubic inch they came out of will fit onto any GMC crankshaft. The width of the bearing tang, the bent portion of the bearing that fits into the notches in the rod and rod cap are what is different. There are numerous rods that have the same forging numbers but can have either size of bearing tang widths and also different wrist pin sizes, so you have to measure both the tang widths and wrist pin size on the rods you have to get the correct pistons and correct bearings. So when it comes to GMC and their forging numbers, the forging numbers are almost irrelevant because so many of them can have both style of bearing tangs and either size wrist pins....Hope that helps!

Okay understood, I kept the old bearings and they fit into the new connecting rod notch correctly and fits well.