Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Sat Apr 27, 2013 9:06 am Post subject: M38a1 head rebuilt (and modded)
The other day I went to the machine shop and picked up my spare head that I dropped off a couple of weeks ago to have it rebuilt and "modded".
He had to replace 1 valve because it was pitted top and bottom and couldn't reface it because there were some pits on one side.
He bead blasted the bowls to smooth them out and the intake to remove any casting burrs that might obstruct flow. He said it all looked pretty good before he did it though. He also took an extra .025" off when he was surfacing the head.
I might mention that this guy has been building high performance engines for about 45 years, so I trust his abilities. I know I am not going to pick up any major amount of power by modifying these engines, but it can't hurt (if done correctly and modestly it won't hurt reliability either). I also plan on balancing the rotating assembly when I save up the money to do the short block. Hopefully this will give me a little more rpm capability without worrying about "grenadeing" it (I know this engine is basically a tractor engine and isn't meant to run at high rpms, but less vibration is a good thing and a few more rpms won't hurt!).
I thought about getting the cam reground, but research shows that the stock cam profile is pretty good for low rpm (torque), and grinding for top end will hurt offroad ability. A Solex carb would help with a little more power, but I want to keep the stock look and I've heard they can be a pain to get dialed in. The exhaust manifold is supposedly a pretty good design already, so I'll check that out just to make sure there are no obstructions or restrictions. The sand blaster with a careful application of StarBlast should remove these problems. I'll remove them if needed and do a port/gasket match. This should help improve the flow. Besides, a Clifford exhaust manifold is EXPENSIVE! I don't know if the stock muffler is a free flow design or not, but it sure sounds like it is!
Hopefully these mods will help produce maybe 10% more hp (80 hp) and torque (125 ftlb), and add a couple hundred rpm capability. _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
None of it hurts but then none of it will ever produce any true measurable power increase unless you put it on a dyno before and after and then it would only be in the 0- 1 HP or so range. These are plodder engines designed to run below 4000 RPM and last a long time. A Solex will not offer any power increase without first improving the engine's ability to flow greater amounts of air/fuel volume. The only way to do that on the Willys 134 is with ram type intakes and headers. And/or a turbo. Dick Hickey has tried all this stuff back in the 60's and the performance answers he left behind are still valid today. A lot of work and money for a very modest increase in HP is all you will ever get. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Mar 13, 2006 Posts: 1079 Location: Richburg, SC
Posted: Sat Apr 27, 2013 10:06 am Post subject:
Understood. Definitely won't add any great amount of power, never will. He charged me $15 for shaving the extra .025" and smoothing up the bowl and intake areas. He said they already looked pretty good, so he recommended shaving the head a little extra.
When I asked about balancing the rotating assembly, he said that since the engine has a long stroke, it can benefit from it, but won't be a cheap process. I think I'll get a quote before I give him the go ahead.
Like I said earlier, there is some information on the net about all of this stuff, but it is really only going to increase the reliability, not performance. Like Wes said, there is a guy (Youtube videos) that put a turbo on his - must not have worked real good, because it hasn't been updated in a while though. I read somewhere that some of the swamp boggers run modded 134f engines, but can't seem to find any info on them. _________________ Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
Keep in mind that shaving the head brings the rocker arms closer to the lifters. At some point the push rod lengths will become too long for the adjustment screw to deal with. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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