Engine Rebuild Suggestions

[Elgin554]

Hi All

New M37 owner. Going to have the engine in my M37 rebuilt. I would like to have it rebuilt so that it provides optimal performance for the T245 type of motor. I do not want to hot rod it but getting it rebuild so that I can drive 55mph for a hour or two duration is desired. So if cam, dual carbs, and dual exhaust is necessary can do- with reluctance. However I would like to keep it M37-stockish as possible. Local engine builder has good reputation but he wants to know exactly what I want done, understandable. So I would like to ask for suggestion please.

Back in the early 1970 or '71 this M37 was transferred to a local county here in the middle of Illinois for Civil Defense service. Shortly after that it was made available to a local fire dept where it was acquired to be converted into a brush truck. That never happened so it sat ( indoors!) for the next 46 years untouched. I now have it and am in the process of restoring it to road worthy condition. Sort of good news is there are rebuild tags on some of the engine accessories some with dates of 67-68. Here is picture of rebuild sticker tag is on the engine block. Of all the searching I have not seen a rebuild tag of similar type so I suspect it may be commercial, or commercial govt contractor. Anyway the block is s/n: P24*405431* which indicated a Plymouth 218CI engine. Sigh. So the plan to take it in for rebuild. This way I can be sure that the internals are that which is required to realize a 230 build. And I can perhaps implement some of the suggestions made here. Thanks.

[Elwood]

Welcome to the G741 forum, and congrats on your truck.

When you state that you want "optimal performance for the T245 type of motor," do you mean that you want all of the military features of the T245 engine, such as the waterproof 24v electrical system? While the P24 engine from a 1953 Plymouth (what's currently in your truck) will obviously work, it has some detail differences from the T245 military flathead six that may or may not be important to you. Some things, such as the pressed in oil fill pipe on your P24, differ from the military block, which has a bolted on oil fill pipe, and are not directly consequential to your 55mph goal. Other things, such as the eight bolt crankshaft and heavy flywheel on the T245 versus the six bolt crank and lighter flywheel on the P24, might be.

Regardless of which engine you build, you'll be pushing it (and the rest of the drivetrain) harder to go for 55mph for hours at a time. Things that weren't important to the military should be on your list of things to do, such as having the crank bearing saddles line honed, the crank dynamically balanced, and the connecting rods and pistons weight matched. Having the rods crack tested, checked for twist and bend, and then polished (and perhaps even shot peened) will help with longevity at 55mph. Out of the box, these engines can be relatively unbalanced, which puts extra stress on the moving parts, especially at the higher rpms you're considering. The performance bits such as dual carbs can be done later - beginning with a solid, balanced engine is essential.

I wouldn't put too much faith in those rebuild tags. The tolerances acceptable in a commercial rebuild, especially one done for a government entity where lowest-cost is the driving factor, might not be as good as you would expect. Until you can disassemble the engine, and inspect and measure everything, you won't know what you have.

[RMS]

x2 on balance and line hone

regardless of the block you chose I would run sodium filled exhaust valves and bronze guides. dragging a seat out of the block with a tuliped valve is never fun. hardened seats and a 3 way grind. plain the head get it up past 7 to 1

[Elgin554]

Thanks for the details Elwood - exactly what I was in search of. This engine indeed has the 2-bolt fanged oil fill pipe and 8-bolt flywheel. By-the-by, the clutch is not even fully burnished and the surfaces on both the flywheel and pressure plate a mirror smooth, really quite beautiful. However, the head bolts are some of the most corroded and pitted bolts on the truck! And I counted about 5 different makers. No telling how many times these head bolts have been 'round the block.

[Elgin554]

Thanks RMS. I will add vales and vale seats to the list. If the pistons are is spec OK to keep or shall I look for a more recent, better metallurgy, alternative.

[52PLOWERWAGON]

order a high performance cam from vintage power wagons

I have one in my 230 best mod I have made to the whole truck

other mods

eliminated the heat riser

fuel pump block off plate and electric fuel pump

I have so much power its like having a smallblock v8 under the hood

[Elgin554]

Here is picture of the oil fill tube flange. Upon closer look it appears to be a press-fit adaptation.
So a Plymouth block... perhaps I can add a Mopar high flow oil pump to the rebuild list.

[Elwood]

Here is picture of the oil fill tube flange. Upon closer look it appears to be a press-fit adaptation.
So a Plymouth block... perhaps I can add a Mopar high flow oil pump to the rebuild list.

Thanks for posting that photo. I was wondering how a P24 Plymouth block came to have a bolt-on oil fill tube.

[Kaegi]

I agree on the cam. I didn't get one from VPW but have them reground locally at Delta Camshafts in Tacoma WA. They can grind it however you want. the stock valve seats are already hardened and out of the 20 or so of these engines i have rebuilt none needed new seats. Run unleaded at will with no worries. I also shave the head .075 to raise compression. before doing that though you need to measure valve height and make sure you have room to go that much. if head has already been shaved might have to go less. I also balance everything, check rods etc.. I have run these trucks at 55 on the highway for 10s of thousands of miles without issues. they are designed that way. they run just under 3200 rpms at 55 which is fine for these engines. you can buy a 2 barrel adapter for under 20 bucks and experiment once its on the road. I have never done 2, 1 barrels or a 2 barrel but some say it helps. I have drilled out the main jet and that helped as well. I went up one size in my drill set. it wasn't much but made a bit of a difference. bigger cam requires more fuel.

[w30bob]

Hi Guys,

No one has mentioned relieving the block............anybody try that? I guess a full relief would be pointless due to the compression drop, but would just a minor relief add any appreciable HP to these engines? I've never seen any actual before/after dyno data on a relieved flathead block.......but it seems to be an "urban myth" that a little relief would really help with the flow. Any thoughts?

thanks,
bob

[RMS]

the hudson inliners relieve their blocks but I think it would be pointless on a zero deck block with flat top pistons. relieving the head around the back of the valves will do. modifying the the ramp and changing spark plug location on the chrysler L heads could be the way to go. these mods can be seen on aftermarket aluminum heads. I do wonder if a small channel on the head starting with a V between the valves leading across the head and down the ramp to a round impression in the head at the center of the piston would aid in flame propagation and help direct the initial force of combustion to the center of the piston rather than just one side.

some ever expanding links on the flat head 6

http://www.g741.org/PHPBB/viewtopic.php ... omposition
http://www.g741.org/PHPBB/viewtopic.php ... lhead+mods

[Elwood]

For those who are wondering what "flathead relieving" is and why you'd want to do it, this might be of interest: http://www.jalopyjournal.com/forum/thre ... to.596271/

I don't know of a small block Dodge/Plymouth flathead six that's been relieved. Has anyone ever done it, or seen one that's been relieved? I wonder how much metal depth is in the area between the valves and the cylinder bores? These engines are already sensitive to localized heat buildup in the exhaust valve area (which is why that coolant tube is stuck in the block), and I'd be concerned about block cracking if too much metal is removed.

[Kaegi]

I don't think it would help at all just be cause the max rpms most of us will probably ever run a straight 6 is 5-5500K rpms and then only in an offroad situation where some wheel speed is needed. I have only had to do that a handful of times and on rebuilt engines of course. it seems the relieving would only help at real high sustained rpms. cam, balancing, shaved head and boring (also raises compression) porting and more carb do wonders to the performance. especially the cam. stock cams are designed for 70 octane fuel. put a modern grind in them and it really wakes them up.

[Elgin554]

Took the engine to the engine rebuilder the other day. It is a rather busy shop, funny how the tone of the conversation changes when you show up with a lump in the bed of your truck to be dropped off. Got to speak with the guys with the dirty hands. Turns out they have built loads of the flat head sixes for Chicago Power Solution (if I recall the name correctly) back in the day when they were a popular stationary power plant. Also they have rebuilt quite a few marine Mopar straight sixes. OK, this is good news. They say the marine build run at 3400 rpm all day. Looks like I will get a marine grind on the cam but they first have to get the motor hot tanked, disassembled, and measured. Getting interesting.

[Kaegi]

that's great news. wish I had a shop that knew flatheads up here. I do get good cams out of delta though. Seems like most of the forklifts, generators, farm equipment on the planet were powered by Chrysler industrial for 50 years. I remember even in the 80s a big shop in Seattle always had about 5 or more flathead 6 mopars on stands ready for exchange.