: where to start on rebuild of 425

04-14-13, 10:38 PM
Hello, I have a 425 in my truck that's going to be getting its first rebuild. Im not looking to build a record breaker, just a good running motor. I realy don't know where to start though, what upgrades are good, and what aren't realy necessary. Any help is appreciated.


04-15-13, 10:35 AM
What makes you feel it needs a rebuild and what areas are suspect? Do you want to do a general rebop to make the engine more reliable? Do a compression test of the cylinders to find out how efficient your cylinders are sealing. Do a vacuum test at the manifold and the carb primary vacuum port. Fluctuations will indicate weak sealing and inefficiencies. If you can, drop the transmission lower inspection cover. Grab the flexplate/torque converter, or put a screwdriver into the space of the torque converter mounting lug and the bolt, and move it back and forth. Just to check free motion of the crank. More than 3-5 degrees and you should replace the timing chain. This can be done with the engine in the truck. There is a plug above the oil pump. This plug is either a square or hex drive pipe plug. There is another plug at the back of the engine, below the manifold. Remove either plug and install a oil pressure gauge. Pressure should be at least 28-30 #s @ idle. Below that, You have problems with the delivery system or the crank bearings. With the engine in the truck, you should be able to drop the pan and check out the bottom end of the engine. :o It is best to have a plan and knowledge before going into an overall, unnecessary rebuild.

04-15-13, 11:12 PM
I do have a thread that explains exactly what's going on and what I'm planning with the motor. http://www.cadillacpower.com/forum/viewtopic.php?f=3&t=15606

The Ape Man
04-16-13, 10:33 AM
Linky is dead here. Why not just start with a 500?

04-16-13, 11:17 AM
Because anything Cadillac is hard to find around here. I realy live in the boonys

04-16-13, 01:01 PM
The 425 is a pretty stout engine, but running any engine low on oil isn't good practice. If the engine oil light (stop engine) comes on, your oil pressure is below 15 #s. You can travel a short distance without doing much damage, but it is highly unadvisable to travel far. Some residual oil in the system may keep the engine moving parts lubricated for the short term. Heat build up will be the killer. Using engine speed to pick up more oil will work on a Chevy or other rear pick up/pump engine, but in a Cadillac or Buick the pick-up is more in the center of the sump area and has a long distance to get to the pump, so lower engine speeds are advisable. You may not have destroyed your engine completely. The condition of the crank and bearings are suspect from what you have described. Go back to my first post and check the oil pressure to find what you have. Use the port above the pump to see what is getting to the pump and through the filter. Running any engine low on oil is unadvisable, but with residual oil in the system you can go a short distance. Once the oil light (STOP ENGINE) light comes on, your engine oil pressure is down to 15#s or less. With a Chevy or other rear pick-up/pump engine increasing engine speed may help pick up some oil, but a Cadillac or Buick of that vintage, the pick-up is more in the center of the sump area, and the pick-up tube has a long delivery to make to the pump, so slower speeds would be advisable. After checking pressure, drop the oil and inspect it for metal particles. If you have cooked it, the oil will have a distinct burnt odor. Remove the filter and use a tailpipe cutter to cut the outer shell off near the mounting flange. Remove the element and spread it out. Small particles = np, chunks, and you have problems. I've described how to analyze your oiling system. The results will determine your next move.

04-16-13, 07:45 PM
Thanks for the reply, I' planning on following your plan, I just started work and waiting for my firs check. The truck is at my parents house and I'm using the last of my savings for gas to get to work. I'm posting under the name robbie thoreson on the Cadillac power forum.are you a member?

04-17-13, 03:35 PM
Both myself and Ape Man are members.

04-17-13, 08:13 PM
Could you please post a working link? I'm doing this all off my.phone and trying to juggle posts on 3 different forums. Wish there was a way to get them all on one page. Lol

04-18-13, 10:27 AM

04-18-13, 11:36 AM
Thank you. Let's say my crank is shot, do you have a recommendation on a new one? Like I said on another forum, I found one from clegg engines for 270. Is that a fair price? And if I get it, do you see any issues ill have if I order pistons and rods from mts?

04-18-13, 08:15 PM
That price sounds fair. You never did tell us how many miles are on it and how bad off it is. If it still runs fine and just knocks then a crank and timing set may be all you need.

04-19-13, 05:35 AM
I'm not sure how many miles are on it. The kid I bought it from had it listed as a unknown big block out of a demo car he just bought . So its had a rough life. It runs, and just barely was making ant valve train chatter.

04-19-13, 10:45 AM
If this is going to be a standard engine, you should first determine the condition of your existing engine before shelling out cash on parts you may not need. I realize you are gathering information, but when you first presented this problem here, you gave us the impression you were looking for an inexpensive fix. My suggestions were centered around that information. If you have followed any of my suggestions, you have not posted the results, so it is difficult to determine what your next step should be. :halo:

04-19-13, 09:31 PM
I haven't even had time to look at it yet, I will let you know as soon as I know

04-21-13, 08:27 AM
More snow later today, some force of nature realy is working against me

04-24-13, 12:01 AM
So I got to work on the truck today. Pulled the distributor out, dumped 3 parts of oil in it and ran the oil pump. After it primed, instantly found my leak... It was the sending unit. Pulled it out and replaced it with a pipe plug. No more leak. Tame the oil pump some more while bumping the motor over to try and lube things up. Replaced distributor, tried to test compression on #1 while finding tdc and it blew the cheap tester off at 150ish so its even higher. It's gust one of the testers with rubber tip that you hold over the hole. Then I found out they don't wana start on water LOL I have a bed mounted fuel cell that apparently snow melt runs right into without a cap. Drained the tank and dumped some fresh gas down the carb, after a few small fires, I'm getting it to technically "run" but ran out of daylight :-) will work on it more tomorrow