Inliners International Forums General Discussion Engines Crow's 250 build thread

So. Preparing to tear down a 250 to the bare block and then all the way back with some improvements on the way up.

First, a little about me. I'm a machinist with more than 10 years experience. Made everything from chicken house floor scrapers to space station parts. These days I do a lot of military and aerospace machining. I've never rebuilt an engine before. Never been deep into a head either. However, I figure with your, my grandfather's and father's help we can do this right.

When I was in highschool my father and I restored a '65 chevy fleetside. Everything was stock. We did nothing to the engine. I gave it back to him because it wasn't safe to drive in traffic in Huntsville and got a Ranger.

The '65 had a 230 with a 3 on the tree. Love that sound and action. (Want to get ahold of one of the 3 speeds with overdrive)

So far I've got and have read Santuccis' Power Manual (might need to just call it the bible), Engine Builder's Handbook by Tom Monroe, Engine Blueprinting by Rick Voegelin.

Recently got a 250 to start building. I chose the 250 as parts are easier than the 292 and it seems to be a more robust engine due to the shorter stroke length.

Don't have a car yet, but am leaning towards a 4 door Chevelle. I've never driven a car much, other than my ex-wife's. It is time for a car.

I want a car that can handle stop-and-go jackrabbit in the city, and smooth highway cruising. And of course; that sweet, sweet, straight 6 feel. A daily driver with teeth.

So, I need an engine with some punch but not an all-out drag car. Really love the turbochargers that some of you guys have been doing. Also, EFI, EIC, wastegate control via a Megasquirt.

Going with a turbo at the level I want means I can probably stay with a stock cam grind and just really have to add forged pistons to the internals.

Don't know much about turbochargers so I'm going to order two of the books that Santucci recommends: Maximum Boost by Corky Bell, Turbochargers by Hugh MacInnes. The other book he recommends (Forced Induction Performance Tuning) is out of print and $135. Unless there is a really pressing reason to get this book, I'll not worry about it.

I realize this is the Engine forum, and not the performance or blown forums. If need be, please move this post to the appropriate forum. However, until it comes time to decide on cam, pistons, turbo, injection, this will be pretty basic. If it's ok, when those issues start I'll ask in the appropriate forum.

Tooling: 90% of the measuring tools in the above books, 6" atlas lathe with milling attachment, drill press, hand tools, ability to sneak some quick stuff on the CNC's at work, bench grinder. Don't know how to weld nor do I have a welder.

Going to be taking pictures at each step of the teardown for my own documentation, let me know if y'all want me to post them.

Anyhow, this is becoming really long-winded. I welcome questions, comments, and criticism.

This is going to be awesome.

Crow.. You are aeesome Can't wait to see your build we'll be here all the way go team crow!!

Crow, Good luck and keep us posted. The hard part will be staying focused on YOUR goals and not letting the over the top guys lead you astray.

Sounds like your off to a good start on your project. We might not have all the answers, but we'll act like we do.

I want a car that can handle stop-and-go jackrabbit in the city, and smooth highway cruising. And of course; that sweet, sweet, straight 6 feel. A daily driver with teeth.

As an alternative to starting with a 150ish hp stock 250, you may want to consider using a vortec 4200 inline 6. They are either 275 or 290 HP stock from GM, add a turbo and at 8# boost you have a 400+ HP engine. Lots of room to install one in a chevelle.

A complete engine (with everthing including harness, pcm etc) with a 4l60E trans can be had for ~$2500 - or buy a rolled/crashed 2WD trailblazer and remove the parts.

You will spend that much money easily to get the 250 upto the stock power level of the 4200.

All the parts need except engine mounts are available now.

vortec4200.com for details

lowboy, Beater, & CNC - thanks for the kind words.

efi - I'm going with the 250 for nostalgia and simplicity. When my father and I restored the '65 I was a stupid teenager. I begged for a supercharged v8 After driving it for a few years I learned to love it. I don't need 400 hp. With a smaller turbo I should have a fast spool and quick acceleration. With the very little that I know about turbos, a .63 AR may be more than enough for what I want.

On pg. 176 of the Power Manual it is claimed that a 250 @ 8lbs will do between 275 and 437 hp. Is this is inaccurate?



This is the current state of the engine. So far I've pulled manifolds, covers, alternator, distrib, powersteering, plugs, thermostat housing.

A little about my grandfather: Several years ago retired from the GM Saginaw plant in Decatur AL. Not sure how long he worked there but I think he was #1 in seniority when he retired. He was a maintenance electrician. Due to recent changes in family type stuff, he and I are reconnecting after several years of strain. He is as excited about this as I am.

Tonight, grandfather and I are going to pull the head. Do I remove valve springs and lifters before unbolting head?

Snot good.

Pulled head and was greeted with this in the 3rd cylinder:



Head:



We really should have pulled the spark plugs and looked inside before buying. Oh well, now we know to do that in the future and I only gave $70 for it.

So, at this point we thought we better have a look at the underside. Upon draining the oil pan, got a lot of water. Gets better and better.

Wasn't as bad as I feared but still not great. Yanked one crank block and one rod block, pretty heavy grooves but they don't seem burnt:



However, the cam has bluing:



The rods have a lot of rust:



Is this worth trying to save? we think it's probably a lost cause. Thinking either the head or the block is cracked. The gasket looked ok.

I think it will be useful as a donor. Should I go ahead and tear it all the way down and magnaflux the crank, block, and head?

If the cam is blue that means it is scrap, right?

AND THIS IS THE ENGINE YOUR GONNA BUILD ??????

Hard to tell until you tear it all apart.

First off,,, Look for a crack on the front of eng block, drivers side head bolt.

Unless the cam bearing are falling out, the cam bearing bores are probably OK.
Camshaft, scrap that & get a custom grind. Stock camshafts are anemic, no performance value at all.

You got it right, keep it simple, stay w/old school tech, crank up the boost & you will be happy w/that old cast iron 250.

Just buy some forged pistons @ the minimum for being able to handle some detonation.

When you get the block, head & crank acid dipped & magnafluxed, that will tell you what is good or not.

" On pg. 176 of the Power Manual it is claimed that a 250 @ 8lbs will do between 275 and 437 hp. Is this is inaccurate?"

Sounds very reasonable to me, to get that would be easy, just need the correct mods to get to 437 HP, but 275 @ 8 PSI no problem.

What was Tlowes make shift 250 w/5 psi turbo engine make? 340 HP?


MBHD

Cowan- Like I said, it's probably a lost cause. It can still be a donor. Magnaflux crank, block, or head?

Yep all 3, need to hot tank them or acid dipped works the best if possible.

Rods also, but those are not a deal breaker if rods are bad, easy to get.

Hank- Thank you. So, I'll go ahead and tear it the rest of the way down and get everything checked. If it's good, great. If not, I can always grab another 250.

I'm for the Vortec 4200 also.

The 06-09 engines can do 350Hp at the crank, with no blower or turbo at all.

http://www.vortec4200.com/forum1/viewtopic.php?f=11&t=987

note: All these dyno numbers are on chassis dynos.

Welcome Crow. Everything said here about the 4200 is true-but it's your choice there is no right or wrong way to go. I agree with Hank, get the parts hot tanked and cleaned first before deciding what to do and what to keep. Throw away the cam. A stock replacement is only $70 but you still could easly do better. Can you please measure how far down in the hole the piston sits at TDC ? Can you als measure how deep the dish is on the stock piston? Thanks in advance Jay 6155

The turbo 250 engine will make more torque than a N/A 4.2
He already stated he wants the 250.

Good luck on your 250 build.

MBHD

The best pull ended at 345@5600 and hadn't reached its peak yet. A later dyno video test with a NA 250 made 350 HP. The potential is there to make whatever HP you want to if your pockets are deep enough.

Thanks,

Just curious as to the peak torque of the 250 w/the turbo @ 5 psi VS peak torque of the N/A 250 combo that made 350 HP & @ what RPMs?

MBHD

jay - I can get you some rough numbers later tonight using a 6" caliper. My depth mics are @ work. Also, the engine is locked due to that really crappy 3rd cylinder. So, TDC will just be a guess or ratio'd off the stroke length for now and I'm not sure what good they'll be.

I can get a pretty good dish depth with the callipers though.

What is your purpose for these numbers?

Going to go grab a pulley puller and hunt up dad's ridge reamer.

Hank, I don't have a print out of the NA engine, it was built by the machine shop owner that dynoed all of Tom's engines for his own personal use, and wasn't part of the testing that Tom did. But the torque for the turbo 250 peaked at 336@4200 RPM.

I am just trying to see how far in the hole different stock pistons are. Some replacement pistons say .085 dish and some .115 dish. All the 250 stock replacement pistons say a 1.640 compression height but GM archives say 1.655 for stock 250 pistons. I am also going to measure and post my 1980 engine specs when I get it torn down. (As soon as I can get some time with my Grandson) Thanks again Jay 6155

Those are going to be the depth of the dish in the respective pistons and not the actual deck clearance of the piston at the quench and spark plug locations.

Hank- I had read about that weak point on the drivers side front hole, and should have looked closely as soon as we pulled the head. Thanks for reminding me. Unfortunately there is a large crack that extends into the water pump hole and both sides of head bolt hole. Here it is outlined with a sharpie:



So, this block is done. I'm going to get the crank and rods out anyways, as they may be useful. Going to have the head checked also. Looks like we'll be hunting up another 250, and now I have a much better idea of what to look for. I bet my grandfather will be up for engine hunting next Friday.

Here is my quick and dirty harmonic balancer puller made from a piece of plate I had lying around:



Drilled three holes with clearance for 3/8 bolts, center hole tapped and drilled 1/2-13. Put grease in the centring cone of the crank and put a ball bearing so the center doesn't get buggered when the 1/2-13 is tightened. Worked fine. To make the drill template just rub the grime on your fingers against a piece of paper or card held against the balancer.

Edit: Jay- Dish was .06 deep by calipers, didn't try to backfigure TDC. Let me know if you want depth mic measurement on dish.

That's cool, 336 ft lbs is dang good for only 5 psi!

MBHD

Thanks Crow! If I understand correctly the .060 is the dish on the top of the piston. Also,the engine is froze because of the cylinder that is full of water. If you can't turn over the engine to get how far down in the hole the pistons sit thats cool. Thank you very much for measuring for me. Jay 6155

Jay, no problem. And yes, .060 dish depth on piston.

Talked to a guy this week who has several 6's for sale. He doesn't know CID except that they aren't 292's. He wants $200 for non-running engines. (running when parked)

I thought $70 was a pretty cheap price, but figure $100-$125 is going rate for a non-running 250. What do you guys think is appropriate?

Offer the guy what you fell comfortable with. If he does not accept your offer, ask what is the lowest he would go.
Does not hurt to ask.

I never paid more than $20 for a complete 6, usually people give them to me just to get it out of there way. Damm V-8 lovers!

MBHD

We saw the guy on Friday. Didn't even try to negotiate as the vehicles/engines had been exposed for a long time and he was claiming he could could get $50 for un-rebuilt carbs. Should have asked him how much he wanted for the carb and manifolds in my garage. :P

After thinking about the 1st engine, I've decided the rust in the 3rd cylinder was probably due to intake valve being open on that cylinder.

Given the state of the 6's this guy had, no way am I paying more than $50 or so and they haven't even been pulled.

On a more positive note, we came across a junkyard full of '60s and '70s cars and trucks. They were closed at the time, going to give them a call this week.

Some of these guys have watched way too many Barrett Jackson auctions and think every old rusted out hulk just needs paint and tires to be worth a million bucks or just gas in the tank and a little more rust to be a "rat rod".