The Opus 250 Rebuild

It's been a little quiet as I waited to hear from my local machinist on the block and the rocker assembly. Finally have some updates to share.

The Rocker Assembly - In another thread, I'd mentioned the difficulty I was having in getting the pedestals to move. My local machine shop offered to dip it in some harsher chemicals and see what they could do with it. Long story short, they couldn't get the pedestals to move either, but were able to completely free up all the rocker arms. Their advice was to re-use it "as-is" instead of mangling it trying to get those pedestals off. I'll shelve that for the time being while I sort out the head and block.

Block and Cylinders - After removing the pistons, I noted that cylinder 1 had a bit of a ridge to it, and it was something I could easily feel. The rest of the cylinders got progressively less "ridgy" and number 6 could really only be felt with my fingernail. Just heard back from the machine shop and they recommend a 0.040 overbore to ensure that the ridge gets removed completely. The lesson I took from this: if you can easily feel a ridge, it's not a good thing.

Compression Ratio - I was waiting to hear about the overbore requirements so that I could calculate the compression ratio. My '73 250 engine has a bore of 3.68 inches, a stroke of 3.91 inches and a piston bowl of about 6.5 CCs. Using the numbers from the Performance Handbook, I figured the stock compression ratio at about 7.6. This increases to a little over 7.7 with the overbore. Since the Handbook recommends a static compression ratio between 8.7 and 9.5, I have some choices to make. Milling the deck by 0.060 only gets me to about 8.5, so I'd need to shave the head by another 0.020 to get to about 8.75. That seems like a lot of milling and some extra work to ensure the head bolts seat properly. BUT, if I go with the 2.5L HSC Pistons and conrods, I can reduce the deck clearance from 0.15 (stock) to 0.04 and get a static compression ratio of 9.2 with a straight swap and no milling.

So I'm leaning towards the HSC pistons and conrods as the best solution to pump up the compression.

Upon further review of Lavron's 250 build thread, I may have gotten some details wrong on the HSC swap. If I'm reading the advice and recommendations right, I should combine the HSC con-rods with the 250 stock pistons (or overbored versions anyway). That will reduce the deck clearance and get me to a compression ratio of about 9.2.

-Mike

:...the advice..."
I'd say "never deck a 250. U take away it's advantage." but:
1) am far from an expert;
2) don't have all the info.
If you chose the 250 (over the 200, etc) Y? Will U loose that advantage?
It all comes dwn to what the final application of the vehicle is...
Yes, the 4 cyl pistons keep the advantage.
Y do U need the cubes/stroked engine?
Have U figured in all the factors (static comp v dynamic, gasket compression thickness, swept area, CCed the haed, etc)?

The advise you received from your Machine Shop to reuse the Rocker Arm assembly as is, depending on their condistion Probably isn't a very good idea. The Rocker Arm Brushings and the Rocker Shafts could have excessive wear, which can reduce total valve lift some and make lots of extra noise. They probally don't have much if any experience with these old Ford Six'es, but No worries your Rocker Arm assembly can be sent in for a rebuild by severial companies that offer this service as well as some upgraded assembly's with adjustable rocker arms. Here are two of them, Vintage Inlines @ https://www.vintageinlines.com Or Rocker Arms Unlimted @ http://rockerarms.com

Glad you checked out "Lavron's" budget 250 short block build if you fallow his lead using the HSC 2.5L connecting rods you can get the pistion deck height up almost were it needs to be without doing a bunch of un nessisary block deck milling beyond a light clean up cut. He did use an Austrian 250 spec piston to get his deck height to near zero, it is looking like it will be be an excellent combo for a street hi performance 250 build. Another possable 250 pistion choice when using the HSC 2.5L rods is maybe the California spec pistons I haven't researched their compression height yet, I do know that in my 1977 Maverick 250 the pistions were .180 down the hole really bad for good cylinder quench yet that engine ran fairly well. There is also the custom forged pistion option from AutoTeh at about $500.00 you get to pick your compression height and ring pack choice too. You haven't stated what you goals are for your 250 Mustang build or outher parts you will be using such as the transmission and rear axel gearing these can have some effect on the engine parts combo too. Best of luck on your rebuild

@Chad and bubba22349 - good points on the missing end goal for the engine and vehicle. My desire is to have a good running street engine that performs better and gets better fuel economy than the original '73 spec 250 engine. No need to defeat anyone in a streetlight drag race, but would appreciate being able to accelerate onto a highway without getting cursed at by a truck driver. I'd like to maintain the look of the engine bay as much as possible while improving the reliability and driveability of the car.

I hadn't considered changing the rear axle or swapping out the existing C4 trans, but I'll admit that I'm only a few steps into a long learning process here.

I measured the pistons on my engine and they were 0.150" down the hole and have the non-California bowls. With the stock pistons, that left me at a static compression ratio of 7.6 that rose to 7.7 with the 0.040 overbore. The HSC con rods bring that back up to 9.3 which feels a little high for a street engine, but I'll gamble on it. I calculated the compression with the California bowls and it dropped it down to 8.6, which seemed a little too low. Not based on any experience mind you, just a gut feeling.

The local shop is still working on the block and just sent the crank out for machining. I had concerns about re-using the rocker assembly, so will take the advice to send it out to a service like the ones you mentioned. It has also convinced me that they're not familiar enough with the engine to handle the head modifications. Once I have the block back and confirm the measurements, I''ll start on the head. I've got a line on another place that may have some familiarity with these engines and will interview them to see about the 1v to 2v intake manifold conversion. Carburetor and camshaft selection are on the "to-do" list.

-Mike

sounds like U want a 1 step performance (MPGs'n pep) improvement over stock.
On the right track then ! Time for carb choice?
U mention an improved machine shop. B sure to ck our recommendations (a forum for that here), make an entry too (if it will be a good or horrible referral) on our forum for that.
I don't re-read all the old posts on these, just the current so want to make sure U use the DSII (ford '77 +) ign w/a '64 + block'n a '68+ carb/dizzy, take care w/the #13 head bolt (can hit H2O pump impeller) when puttin in (coat w/water proofing goo 2).
Keep us informed & thanks for bringin us (me) along !

BTW: 'opus' ? musician? artist? me too

What camshaft are you going to use?

@chad - yes, been looking through the recommendations and asking around within the local Mustang club. I'll definitely post a good or bad experience once I get the head back.

The only part of the ignition/carb setup that I've settled on is the desire to modify the head for a 2 barrel carb. That big old log manifold just seems like it ought to have twin barrels feeding it. Need to educate myself on installing con-rods and press-fitting piston pins before I tackle fuel and air, though. Between YouTube and this forum, I figure someone has made the mistakes for me.

Opus refers to Opus the Penguin who has been sitting (or tailgunning) in the rear window of the car since 1986. But I'm also an amateur musician who plays a little bass guitar from time to time. You?

@pmuller9 - that's a really good question! Assuming the block comes back from the machine shop without any additional metal removed or other complications, I should be able to get the head modified and then finalize the static compression ratio. Then I figure I can start working out the camshaft profile with some confidence.

"...You?..."
yes, thnx 4 askin: bass/baritone for a Black Gospel Choir, sax, trombone & trap set (some blues, ragtime, pop) but the real artistry comes w/the writing. A world wide method started here I just hada try (Amherst Writers and Artists). Never tried till then (6, 8 yrs now?) and was always told "No, U can;t write". I am a story teller (family tradition) so these ppl really sanctioned me - all I really needed. Enjoy it now - wrks w/same stuff all of it duz (theater, sculpting, dance, flat art, photography) the personal biographical & emotional we all possess.

Just got the machined block back from the shop. Cylinders are all overbored 0.040 and crankshaft only needed 0.010. Bearings are on order and I've got a new set of skills to learn now like prepping and painting a block, putting together press-fit pistons and pins, and learning the ins and outs of camshafts. The journey begins! Although with winter temperatures already settling in, it may be a lengthy journey.

@chad - nice. Bass/baritone is a talent and skill I can admire and congrats on the writing. Figuring out how to graduate from a string of notes to pieceing together a full song is on the list for me to tackle one day.

I like the 'handy' stuff (house building, futzin w/my 50 y/o bronk) but w/never writing or singing - now asa ol guy it certainly is fulfilling. I find music to tap the spirit/emotion, the writing to be expressive and self exploratory even tho not abt me - my stuff comes out, I get to look at it, understand myself better (pretty deep level).

There are degree wheels on-line U can print out if like me - U wish to take the low budget way. Local big box houses (AutoZone, etc) may havea loaner too (also free of cost). Keep us informed !

OpusTheTailGunner":wbuvw1fy said:

Just got the machined block back from the shop. Cylinders are all overbored 0.040 and crankshaft only needed 0.010. Bearings are on order and I've got a new set of skills to learn now like prepping and painting a block, putting together press-fit pistons and pins, and learning the ins and outs of camshafts. The journey begins! Although with winter temperatures already settling in, it may be a lengthy journey.

@chad - nice. Bass/baritone is a talent and skill I can admire and congrats on the writing. Figuring out how to graduate from a string of notes to pieceing together a full song is on the list for me to tackle one day.

Click to expand...

Congrats seems like the machine shop did the block work fast! Did you acquire a rebuilt set of six of the HSC 2.5L connecting Rods for your short block build up? If so you should then have your machine shop press the new set of pistons and pins on the Rods, it takes some special equipment to be able to do that job. Best of luck

Yes, the shop turned it around quicker than I was expecting. I've been ordering parts in the meantime, so have 6 of the rebuilt HSC rods and 6 new 6.5cc dish stock pistons and a set of ARP rod bolts (289/302). Naturally, Youtube makes pressing pins into rods look easy (https://www.youtube.com/watch?v=2lHadmX4mpo), but I may yet just include that job with the yet-to-be-sorted-out cylinder head adaptation.

For the record, here's the static compression ratio numbers I'm working with:
Bore: 3.72 inches (0.040 overbore)
Stroke: 3.91 inches
Stock deck clearance minus HSC con-rod length increase: 0.150 - 0.110 = 0.040 inches down the cylinder
Head Gasket assumed to be Fel-Pro with 0.05 inch compressed height and 3.75 inch bore
Piston bowl volume: 6.5cc or 0.397 cubic inches
1980 Cylinder head combustion chamber (from Falcon HB): 62 cc or 3.784 cubic inches

Put it all together and the compression ratio comes out to 9.24. So far, some initial dynamic CR calculators are projecting around 7.5 to 7.7 depending on the IVC timing (64 to 60). Here's hoping reality matches the math. 8)

Yes for sure you can install the Pistons like is done in that video, it is easy if you have a good torch (note that he is also using Map Gas which is the best for this since it burns much hotter than Propane Gas) if you take your time getting the Rods small end heated right and then install the pin quickly before it cools down. There are a couple of things that will be a bit different since the video is for a Small block V8piston and Rod. On your 250 Pistons there will be a notch that's points to front of the engine and also the rods will go on so that the rods cylinder number will be all on the same side of the short block (check that on your orginal rods and Pistons) that's all the difference. Excellent! Glad to hear that you got those HSC Rods that's the best budget Way in reducing much of the excessive Quench Distance of these 250's. Yes your math is very close except for the piston compression height of the replacement Pistons is different.

Here is the static Compression Ratio I get for your 250 long block combo.
3.720 Bore Size (.040 over bore)
3.910 Stroke
1.500 Piston Compression Height, the aftermarket cast replacement Pistons have .011 less in compression height than the orginal stock Ford Pistons had.
6.5 CC's Piston Dish
.051 Deck Height (Piston Down the hole)
.050 Thickness for the FelPro composition head gasket
.100 Quench Distance using the HSC 2.5L 5.990 lenght Con. Rod with .040 over replacement 250 pistons.
3.810 FelPro Gasket Bore Diameter
62 CC's Combustion Chamber on stock Ford 250 Head.
9.01 to 1 stock Compression Ratio
255 Cubic Inches

All specs as above except using the Victor .044 head gasket
.094 Quench Distance is .006 less
9.12 Static Compression Ratio

Notice with a small change the quench distance the compression ratio can change quickly and Idealy the Quench Distance should be around .050. This would rasie the CR to 9.93 range which for pump fuel you would need bigger dish volume in the Piston tops to bring it back in range.

All specs above except for using the stock 5.880 length 250 Con Rods.
.211 Quench Distance
7.54 to 1 Compression Ratio

This will be a great performang 250 with good 1 1/2 + point increase in the compression ratio over the stock 250 and depending on your area condistions it might even still run on 87 regular pump gas. If you wanted to increase the CR more if you plan on using a higher grade fuel than the best bet would be to reduce Quench distance even more by milling the block deck some and or you can use the Victor head gasket which is a 0.44 crush thickness (see this in the above second example). This would be better way forward on rasieing the Compression Ratio on any of the 250's short blocks than milling the heads combustion chambers smaller to raise the CR.

Also in my above post #4 inquiring on your plans for the trans and rear axle, to be clear I wasn't suggesting that you needed to change out the C4 (I like these transmissions a lot and have used them in many of my car builds) plus your 1973 Mustang already has the best of the best in C4's (a 1972 up version with all the factory improvements) they only need a couple things to improve them. First off I always use a TransGo shift kit for its quicker shifts this makes the trans last longer I also add a small trans cooler again this also makes the trans last longer by getting rid of excessive heat. After that I might switch the servo cover to help them it depends on which one you have now. There are also other Mod's but these are the first ones and are the best and at a reasonable cost that you could do a little at a time. On rear axle again not saying you need to change it I was just wondering on the gear ratio it's has now. One final thought with coming cam choices the early 1969 & 70 250 had the best timing gear and chain set to use for a performance build let me know if you need the part numbers for it. Best of luck on your 200 build up

Sorry for the time gap - had to replace a few parts on the daily driver and rush to prep, prime and paint the block while the temperatures held in the 70s here in Michigan. Figured it was either rush to get it done or wait until next Spring. It was a spray can job, but I'm not unhappy with the results:



@bubba - thanks for the heads up on the piston height. I never saw a reference to that during my thread scanning, but took a look at the new vs. old, and look at that - the top land is just a little bit shorter on the new pistons (right around 0.01" if you ignore the freehand measurement error). My updated CR calc with the additional 0.011" now matches yours and I'm satisfied with the increase. If I'm able to use 87 with the engine, all the better. Also thanks for the notes on the C4 and the axle - I'll keep that info handy when I get to those steps.

New Silv-o-Lite 1120 (+0.040) Piston:


Factory Piston:



-Mike

Your welcome Mike, that block is looking great too with the.fresh paint job.

A brief and long overdue update while waiting for winter to loosen its grip and bring the workshop back above "wow, it's cold in here" temperatures. After a brief exchange with Schneider Cams, I chose to go with their 262-70H camshaft. They recommended that or the more pedestrian 256-H and I chose to go with the "hotter" version. So just need to buy a replacement timing chain and I'll have all the parts in place for the bottom end rebuild and cam degreeing exercise.

Out of curiosity, I looked into the ARP stud kits for the main bearing caps, but could only find a set for the 240/300. After a brief exchange, ARP confirmed that these studs are 7/16 x 14 x 4.0" which appears to be a 1/2" longer than the bolts I removed from the 250. I also tracked down a set from Speedmaster, but these kits seem to only have 10 studs and not 14. I'll do a little more digging, but may just use the stock bolts in the end.

-Mike

Hi Mike gald to hear your up date on the 250 build. Not sure if you need this info or not for choosing a timing chain and gear set, but here goes. The best available timing gear set (and chain?) we have for use in a Ford (US specs block) 250 performance build up is the one from the 1969 to 1972 engines, the info and part numbers needed to ID' the early sets gears and chain is listed below.

The early 250 engine used a narrower timing chain and gears this was stock on the 1969 to 1972 250 Ford six's. It has cam timing that is set straight up, since there isn't any aftermarket duel timing sets being made this is recommended as the best of the 4 stock available timing gears / chain sets to use for either a mild and hi performance build up. It has the Cloyes # S414 Cam Gear and # S415 Crank Gear. I haven't heard of any company still selling these early timing sets as a complete package, but you can still get all the indivagual parts to make your own set. These links are current with one available of each at the time I posted this.

Early 250 Narrow 1969 to 1972 Timing Chain Cloyes # C363 = $23.79

Early 250 cam gear 1969 to 1972 Cloyes # S414 used with the # S415 crank gear $23.79
https://www.rockauto.com/en/catalog/for ... ocket,5722i

Cloyes Crank Gear #S415 used with both above # S414 and second Cam # S442 gears $14.93
https://www.rockauto.com/en/parts/cloye ... ocket,5723

You can also see studying the excellent pictures of this early timing chain set and the second generation 1973 to 1976 timing set below from a the Post made by site member "Econoline" were he did an extensive study comparing and identifying all the timing gears and chain parts. It's also interesting that the second generation timing set use the same crank gear as the early set plus uses the wider timing chain so the wider timing chain may even fit on the early cam gear which would be the strongest chain I don't know. Check your timing chain and gears against this info. Best of luck.


Post by "Econoline"
"I know this has been discussed and I have read through all the various topics posted regarding the timing set for the 250 but I am still a little confused. I want to replace my timing set so I've been looking into it. My 250 is a '70 and I understand I want a pre '73 chain.

There has been a lot of discussion that the available sets are all late era retarded. But when I look for a set I find 2 different sets available from at least 2 companies and probably sealed power as well (with a couple of hitches ). First are the ones available @ Autozone and Advanced Auto and maybe elsewhere, the "SA Gear" #73083 @ $38 for '69-'72 250 & #73016 for '73 on. Next is Cloyes, while no set is available" "Here are the Key Parts for the 1969 to 1972 Timing Chain Set" for 69-'72, parts can be bought to make a set those being #C363 chain, #S415 crank, and #S414 cam @ ~$70. The '73 on is available in set #C3016 with the only part difference being the cam sprocket #S442 vs S414 for the early version.

To complicate things further, I present these 3 pictures, notice the "SA" in the casting.

Cloyes S414:


"SA" late:


"SA" early:


"On the "SA" late set, if you look close, you can see S442 on the cam sprocket as well as "SA" and so on and S415 on the crank sprocket showing that this "SA" set is in fact Cloyes."

On my build, I did not want the CR too high so I could easily run pump gas that was readily available the machinist calclated it in the low 9s (9.1-9.2) with the stock ford 200-250 pistons and 12- 13 cc dishes he cut on the stock pistons I think I said in after sight I should have ordered the California emission pistons and saved the expense of the custom machine work but the brain was not working very good that day I guess if you go with Tempo connecting rods I got my from Clegg Engines in Nevada, you have to use the Tempo rod bearings BTW.
I had the machine shop install the pistons on the rods because he had the equipment to do it and it wasn't too expensive IIRC, probably cheaper than me trying to buy the stuff I would need to do it myself one time. I bought an early timing set from Clay Smith when I did mine, don't know if they are still selling those or not.

I can't say enough about how well my 250 runs, it is super impressive, the only car I have ever owned that can pretty much cut the rear tires loose at will so it is a good runner IMO and so far lots of fun, I will relink a few youtube vids below of it running if you haven't seen them, if you have just don't click the links.

250 First start and Cam break-in

250 Cold Start After final valve adjustments

Getting to finally hear the 250 run without all the exhaust rattles finally

Liike I said all of these are posted someplace back in this build thread but put them here for convience.

See Ya,
Mike

bubba22349 said:

Hi Mike gald to hear your up date on the 250 build. Not sure if you need this info or not for choosing a timing chain and gear set, but here goes. The best available timing gear set (and chain?) we have for use in a Ford (US specs block) 250 performance build up is the one from the 1969 to 1972 engines, the info and part numbers needed to ID' the early sets gears and chain is listed below.

The early 250 engine used a narrower timing chain and gears this was stock on the 1969 to 1972 250 Ford six's. It has cam timing that is set straight up, since there isn't any aftermarket duel timing sets being made this is recommended as the best of the 4 stock available timing gears / chain sets to use for either a mild and hi performance build up. It has the Cloyes # S414 Cam Gear and # S415 Crank Gear. I haven't heard of any company still selling these early timing sets as a complete package, but you can still get all the indivagual parts to make your own set. These links are current with one available of each at the time I posted this.

Early 250 Narrow 1969 to 1972 Timing Chain Cloyes # C363 = $23.79

CLOYES C363 Timing Chain | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

Early 250 cam gear 1969 to 1972 Cloyes # S414 used with the # S415 crank gear $23.79
https://www.rockauto.com/en/catalog/for ... ocket,5722i

Cloyes Crank Gear #S415 used with both above # S414 and second Cam # S442 gears $14.93
https://www.rockauto.com/en/parts/cloye ... ocket,5723

You can also see studying the excellent pictures of this early timing chain set and the second generation 1973 to 1976 timing set below from a the Post made by site member "Econoline" were he did an extensive study comparing and identifying all the timing gears and chain parts. It's also interesting that the second generation timing set use the same crank gear as the early set plus uses the wider timing chain so the wider timing chain may even fit on the early cam gear which would be the strongest chain I don't know. Check your timing chain and gears against this info. Best of luck.


Post by "Econoline"
"I know this has been discussed and I have read through all the various topics posted regarding the timing set for the 250 but I am still a little confused. I want to replace my timing set so I've been looking into it. My 250 is a '70 and I understand I want a pre '73 chain.

There has been a lot of discussion that the available sets are all late era retarded. But when I look for a set I find 2 different sets available from at least 2 companies and probably sealed power as well (with a couple of hitches ). First are the ones available @ Autozone and Advanced Auto and maybe elsewhere, the "SA Gear" #73083 @ $38 for '69-'72 250 & #73016 for '73 on. Next is Cloyes, while no set is available" "Here are the Key Parts for the 1969 to 1972 Timing Chain Set" for 69-'72, parts can be bought to make a set those being #C363 chain, #S415 crank, and #S414 cam @ ~$70. The '73 on is available in set #C3016 with the only part difference being the cam sprocket #S442 vs S414 for the early version.

To complicate things further, I present these 3 pictures, notice the "SA" in the casting.

Cloyes S414:

"SA" late:

"SA" early:

"On the "SA" late set, if you look close, you can see S442 on the cam sprocket as well as "SA" and so on and S415 on the crank sprocket showing that this "SA" set is in fact Cloyes."

Click to expand...

On my build, I did not want the CR too high so I could easily run pump gas that was readily available the machinist calclated it in the low 9s (9.1-9.2) with the stock ford 200-250 pistons and 12- 13 cc dishes he cut on the stock pistons I think I said in after sight I should have ordered the California emission pistons and saved the expense of the custom machine work but the brain was not working very good that day I guess if you go with Tempo connecting rods I got my from Clegg Engines in Nevada, you have to use the Tempo rod bearings BTW.
I had the machine shop install the pistons on the rods because he had the equipment to do it and it wasn't too expensive IIRC, probably cheaper than me trying to buy the stuff I would need to do it myself one time. I bought an early timing set from Clay Smith when I did mine, don't know if they are still selling those or not.

I can't say enough about how well my 250 runs, it is super impressive, the only car I have ever owned that can pretty much cut the rear tires loose at will so it is a good runner IMO and so far lots of fun, I will relink a few youtube vids below of it running if you haven't seen them, if you have just don't click the links.

250 First start and Cam break-in

250 Cold Start After final valve adjustments

Getting to finally hear the 250 run without all the exhaust rattles finally

Liike I said all of these are posted someplace back in this build thread but put them here for convience.

See Ya,
Mike