hi every one i have question just got 248 6 banger that looks to be in good shape.Dose any one have one all tricked out in their ride that i could get an idea from.Or any one have any tricks or mods for these engines or even pros and cons about this old stovebolt. thanks guysits for a 58 apache
Mine is a 320 inch jimmy ( 302 .125 over). Dont put a lot of effort in the 248. You should be able to find 270 or a 302 for not too much. I paid $125 for my last 302 look for a big gmc truck with 20 inch wheels. 302s have 2bbls on them. the displacement is the first three digits in the serial number on the pad beside the dist. 270s besides the elusive 51-52 H port are pretty common. They were in all of the gmc light duty and most medium duties from 55 - 62. Flywheel and starters from these are used when you put 302s in something with the small bellhousing. Just a little fyi Jimmys really aren't stovebolts. Thats a chevy term. Most stovebolts suffer from long motor envy up next to a Jimmy. Jay
oh thanks for the facts boss, this is what i got to work with any tips other than getting rid of it after i drove 200 miles to get it.thanks
You see alot of stuff about chevy sixes, is there much speed equipment, aftermarket support for the gmc's. Do any of the parts interchange?
Thank you someone else also knows how great these GMC's are. Wicked you should pick up the inline hop up book for the jimmy's. Great little book.
My 270 that I just did some internal damage to. Gotta pull the oil pan tommorow and have a look but it doesn't sound good. Must have been the hard time I was giving it...
Not my fault that you drove 200 miles for it. You can make any thing faster than stock, however a 248 starts out low on the totem pole. If you are serious about wanting a Jimmy, I would think that you would want the maximum results for your effort. You will need to increase the carburation, install a bigger cam, and ultimately raise the compression. The cylinder head on the 248 needs a great amount of work to have decent flow. Most all of the aftermarket intakes are based on the 1 3/4 port size of the "H" port or the 302 head. The 302 head will accept SBC valves with a minimum of effort, this will give you a great increase in flow. The only downside is that the combustion chamber is pretty big, so custom pistons $$ are really necessary to have decent compression. Mine has 9 to 1 Venolia popups in it. The late 270 head may be a better choice for you. The chambers are much smaller and will yield a better compression ratio with a flat top piston. Your 248 may or may not have flat tops. This head also has the small port so work be required to use the big port intakes. You can use the same exhaust manifold/headers on all of the small block jimmys Several are available from split stock manifolds on up. In your post you mention that it is for a 58 Apache. Jimmy s do not "bolt in " where a Chevy six fit. They are longer, and in 1955 ( I think) went to a front mount that your 248 may or may not have bosses for. Bottom line it costs the same or even slightly less to build the 302 vs the 248. I have around 1800 to 2000 in mine. I realize that you may not want to go that far. I hope that you find this more helpful. Jay
<TABLE id=HB_Mail_Container height="100%" cellSpacing=0 cellPadding=0 width="100%" border=0 UNSELECTABLE="on"><TBODY><TR height="100%" width="100%" UNSELECTABLE="on"><TD id=HB_Focus_Element vAlign=top width="100%" background="" height=250 UNSELECTABLE="off">Hi Arch - dont let bigport Jimmy fill you full of shit. CID on 6 cylinders doesnt determine how much fun you can have. Lots of guys have been having lots of fun with the Chevy stovebolts for a long time. If you want to make your 248 into a 270, just swap the 270/302 crank in them and go with a conservative rebuild - none of the .125 over crap unless you have to bore it that far - that just ruins good blocks. Do a good rebuild and then be careful with your trans and rear gears and you will have a great runner. For the street the smaller port heads will be just as good as the big port heads - maybe better. Join Inliners and you will have a ton of technical help. </TD></TR><TR UNSELECTABLE="on" hb_tag="1"><TD style="FONT-SIZE: 1pt" height=1 UNSELECTABLE="on"> </TD></TR></TBODY></TABLE>
I don't recall telling him to overbore his .125. I mentioned that mine is How is telling him that lots of people build Chevys help him with the 248? I did not think about using the 270 crank in the 248. That still doesn't solve the cylinder head issues. Besides generally the easiest way to get a 270 crank is in a 270, so why not build a 270 to start. Money is money so why not use it to the maximum effect, and start out further up the hill than a 248. Thats the only point I'm trying to make. Cid doesn't equate fun you can have fun with a 5 horse briggs. Jay
kind of a smart ass arent you? The point of telling him that lots of people build Chevys is to tell him that he doesnt HAVE to go get a 302 to have fun. You can dance with the one that brung Ya, you know? The Chevy versions did not have as many cid as the GMC's, remember?? Since 248 is bigger than 235 he has a bigger displacement engine than the Chevy counterpart. So what if it isnt a 302? Another way to find a 270/320 crank is to ask around and see who has one. Why buy lots of parts you dont need or want (ie another engine). You are right - money is money, so why waste it? My point about the 248 is that he already has it and if he is patient there are lots of ways to get what he wants without throwing it away and buying a 302. So why ping the guy? he is looking for advice - help him out and dont tell him he screwed up. Can you tell him how to solve the cylinder head issues or just tell him he made a mistake and buy another engine????
A far as cylinder heads go I was reading an article on GMC heads recently (December 2007 issue Austrailian Street Rodding) and it said that a early Toyota Landcruiser F/2F/3FE cylinder head is a possibility on a GMC. Dunno how true this is but we are presently trying to track one down to check it out. First off we are going to compare head gaskets between the two motors. I could scan the article if anyone is interested. Send me a PM if you would like me to email you a copy. Meanwhile, we found the 'knock' in the GMC. The flywheel has come loose (again) Anyone got any secrets for keeping the bolts tight as this has to be the third or forth time this has happened.
Been there, done that. It will not fit a GMC or a Chevy or a Holden FJ. The stock GMC came with a link washer that went between two bolts and the ends bent up to lock the bolt head from turning
You running a 6 bolt flywheel? if not,you might need to drill and tap extra bolt holes,best to do with the crank at a machine shop.If you have 6 bolt wheel,ARP Pontiac V-8 stick flywheel bolts will fit and are better than old stock ones.Red Loctite helps too.
Thanks for the replies. It only has 4 bolts holding the flywheel. Might have to look at something like the ARP Pontiac bolts. If they fit in a 6 bolt situation then they should be suitable for a 4 bolt. We would like to convert the flywheel to 6 bolt but don't really want to remove and pull the motor apart just to do that. It is a must do next time the motor is down.
So I'm a smart ass yet you are the one who is telling him that I am full of shit. All I offered was my honest opinion on the situation. The problem with asking around is that he drove 200 miles to get a jimmy. It might be like around here there aren't many of these trucks/ parts around. If he gets a 270 crank he will probably need the 6 bolt flywheel off of it. I also recommended that he use a late 270 head. This will probably mean that his pistons will have the wrong design dome. So then he needs new pistons. I still think that he would be ahead of the game to find a 302 or late 270, if he wants to build a performance oriented jimmy. This is my opinion based on my experience with my GMC. My point is if you need to change all of these parts, you will be ahead to have something that starts with at least some of them.If not the 248 will make a good engine for his truck within its limitations. I should have been a little clearer in the beginning. It may all be moot as the 248 may not fit in his truck, with the motor mount situation. Jay
I ran a 270 GMC with the four bolt flywheel. I did redrill the crankflange for the later 6 bolt flywheel. It ran good and I liked it. I think a 248 is OK for the street any day, if that makes you happy. BNI/SCTA XO/BGAlt record holder.
thats part of my problem that the mounts are different, also thinking of using a 4 speed saginaw. but how do i adapt it to this 248 which is set up for a 3 speed top loader? any ideas. thanks for all the feed back but im looking for a cruzer not a racer. i just want to get it on road you know.
Any of the 1948 up through 1962 1/2 ton truck bell housings will take the modern 3 or 4 speed patterns. Do you know what year the 248 is? The mount on the early bellhousing that goes to the crossmember is flat. The ones to fit the 55-59 gm truck has a slanted rear mount. I have seen late into early, but not the other way. Also 6v and 12v fly wheels and starter will not interchange. The starters have the same boltpattern, but a different bendix. I am almost certain that you can interchange the ring gears to match your starter. If you have a later flywheel you can run a 10 inch small block chevy clutch and pressure plate, just be sure to get the right height throwout bearing. Some of the early 4 sp may have had the pattern for the bigger pressure plate. Most of the 3 sp had a smaller clutch and I am not sure if the bigger plate will fit. If your block has the bosses on the side you shoul be able to find the saddle mount for your year of truck. It looks like a big U with the mount on the bottom. If not maybe you could make a plate fom the front cross member to the frount mount. One other thing to consider is that the balancer on these motors is prone to flying apart. They also have the annoying habit of being a 7/8 or a5/8 belt. The easy fix is to modify 292 chevy balancer to fit. You also have to change to a 3/8 belt 270 waterpump, but they arent exspensive. If you want some details on thje balancer or have any questions shoot me a pm. Jay
It has been a long time since i ran a GMC but I don't think the 6 and 12 volt ring gears can be swapped. The six volt had such deep teeth on it I'm pretty sure the inside diameter was smaller. Maybe not.
Yeah,something like that.The early 6 hole wheels are worth more actually.The big truck goofy recessed flywheels are useless ,a flat 11 inch clutch flywheels with a Ram diaphram clutch will clear a early 50's Chevy truck 235 bellhousing
Archie can you post the casting number on you cylinder head? If it is 2194819, it is the same as a 270 head. I did not realize that they put some of these on 248s. I was just checking some reference material and that jewel popped out. Jay
We would like to convert the flywheel to 6 bolt but don't really want to remove and pull the motor apart just to do that. It is a must do next time the motor is down.[/quote] On my 322 we just redrilled a chevy manual flywheel and put it on the crank. I forget which holes lined up but only a couple had to be redrilled etc. Works for me. By the way you have a super nice car...
Looking at the bore sizes and bore center distance - is the late 230/250/292 developed from the GMC? Certainly the distances are closer than between the 230 and the 216/235/261 series.
The late motor has no commonality with the 270-302 series. I believe the engine size will be written in the first three numbers stamped on the distributer mounting boss.
If that old '248' runs fair, split the exhaust manifold. You can have a heck of a lot of fun, right off the bat! And with some gears you can run down the road as fast as the law will let you go and a little more! How ever if you want a THUMPEPY THUMP THUMP fire snortin GMC 6. Then no you should not mess with the '248' any of the old jimmy motors will dress up and look good.
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