For those that have never tried it before a performance build on a Ford small block inline 6 has it’s own unique set of challenges, certainly there are few companies that even produce parts since Ford dropped the small 6 in the early ’80s, while all the small sixes look nearly identical, besides changes in bore stroke there are some internal differences as well that keep many parts from interchanging. 144-200cid motors are exactly the same size and interchange easily, the 250 is the odd duck as it is taller, wider and longer (thanks to the water pump) than the others that can present challenges when installing one to replace one of the other displacement motors.
Originally my car came with a 170, I still own this motor, it is the original engine I modified, I did this in the ’80s before we had the internet (yes there was a time) so you were on your own building one and I really did not realize that it was not the best choice to do a performance upgrade on, while I think the motor is a good well-built engine the big difference between the 144 & 170 versus the 200 and 250 is the number of main bearings, the smaller motors have 4 the bigger motors have 7 so I decided with this build I would opt for a 200, it would drop right in and when I bought a parts car the guy threw in a complete but stuck 200 out of a ’72 Maverick Grabber, I was able to free the motor but some of the cylinders were pretty rusty (the piston rings were broken in cylinder 6 as well, probably what killed the car), I do think it could have been bored out and cleaned it up I never got that far (short block is still sitting on a stand in my shed)
Enter the 250
The whole idea behind the 250 came about for a couple of reasons, first was when I was researching the adapters required to install a T-5 transmission on the 200, along with clutch parts that were getting a bit rare to find, I discovered the 250 used a small block V8 bell housing bolt pattern, I could simply bolt a T-5 directly to the 250, no adapters, no custom parts. The second reason is I knew where there was a cheap 250 in one of the local scrap yards. Finally I got bit by the challenge of the 250 bug.
I was concerned the motor could be stuck as well because it had been in the yard quite some time like you see it here without a carb and the hood open. I asked if it was ok for me to pull the head and check the motor out and they said, by all means, this is when I discovered the head had a significant crack right across the carb mount that extended all the way down to the exhaust ports and I could not tell how far across the cylinders, I opted to not take the head, the cylinder walls looked good, no rust even though there was a little water in oil pan it had not been there very long and did no damage. The odometer on the car read 68,000 miles and I believe from the condition of the motor that this was correct and had not rolled over already, the only issue is it appeared the oil had never been changed in the car.
The 250 is not the holy grail of the small sixes, in fact, it is not all that popular when compared to the 200 mainly because of the size difference they make for a difficult swap from one of the smaller motors. If you were wondering why they are larger, the 250 is a stroked 200 and the crank throws are so close to the camshaft in a 200 that they had to widen the motor and make it taller to move the cam far enough away for them not to interfere with each other and while the 200 and 250 share piston size (interchangeable) the rods on a 250 are longer, obviously the cranks are not interchangeable, I believe the main bearings on the 250 are the same as a small block V8 and the 200 mains are smaller, but don’t quote me on that, the cams will interchange as well as the heads on all the motors, the engine is only longer because the 250 uses a unique water pump with a long snout.
The other issues with the 250 are when it was built, 1968-1980, for those of us that lived through that time we can remember it was an era of Detroit detuning cars because the oil embargo and gas shortages, the 250 suffered from this in the area of being a lower compression engine that had a severe piston/deck shortfall, that means at TDC the piston does not reach the top of the engine block deck by quite a bit, not good for performance and venerable to ping, my 250 pistons were around a 1/8″ down the bore at TDC.
Addressing the 250 Block Shortfalls
There are a couple of ways to remedy the piston shortfall, most simply mill the top of the block down to the top of the piston, this raises compression and lessens the issue of pre-detonation (ping) the only problem here is, in most cases, you can’t deck the block that far without severely weakening it (or ruining it). Another way is to put longer piston rods in, raising the piston in the bore, the issue here is where do you get the rod because no one makes aftermarket rods for the 250 (no one makes standard rods either) a little research yields the perfect rod; 1986-91 Ford Tempo/Topaz 2.5L HSC/OHV rod, only problem, they are rare as well, but I was able to obtain 6 refurbished rods.
The Tempo rod is a nice forged unit and specs are identical to the 250 rods except for the length, one thing to note is you need Tempo rod bearings, even though the specs are the same the bearing centering tab on the Tempo rod is different, I didn’t have any trouble getting the Tempo bearings (after I bought 250 bearings I couldn’t use, they were cheap though, like $2.50 a bearing) Now you know so don’t make the same mistake I did.
Adding the Tempo rods and slightly decking the block brought me to nearly zero deck height, the machinist did have to cut slightly bigger recesses in the tops of the pistons to control the compression ratio, another tip for you I wish I would have thought of before I had him cut the larger reliefs would have been to use a set of California emissions pistons that have a 13mm recess about the same as what we removed.
Machine Work on Block
Basically after a good cleaning and check to determine if the block was sound, a .030 overbore was done to clean the cylinders up fully, cylinder hone and a small amount of decking (he did not tell me how much he removed) the crank was ground .010 under and rotating assembly balanced. The machinist also pressed the new pistons on the Tempo rods and added ARP rod bolts (same as a SBF), and installed the new cam bearings, he also painted the block blue which is not what color it will stay (prior to about ’65 or ’66 Ford blocks were black)
I installed the rings, pistons, main & rod bearings, a Howard’s cam with a stock ’67-’72 timing chain set. (more on this on down under valve train)
The Modified “M” Log Head
Ford offered many head variations through the years, all are interchangeable across all the motors, and all US heads have an integral cast on intake (bad for a performance build) in my opinion the best US-made head is the one that came on the ’78+ 200 and 250s, they have the biggest intake valves and hardened seats with the “M” flat log head being the best (“M” is just a part style designation cast into the head, it is a large intake log with a flat top)
The only problem is my head is not the best one, remember the 250 head was cracked so it came without one, the ’72 200, however, had the flat top “M” head on it and since they interchange I used it, it was not that difficult to add ’77+ plus specs to the head by cutting the intake valve seat larger adding hardened seats to the exhaust valves and using a new set of valves for a ’77+ motor (a couple valves had to be de-shrouded), also new valve guides were installed and the head was milled enough to clean it up. Also, an exhaust port divider was welded in to separate the 3-4 siamese port into two and then the exhaust flange was milled flat (he also removed 3 broken off header bolts). A little bit to help improve performance, a set of valve springs initially from a ’74 Torino 302 exhaust side and one-piece spring retainers and new keepers were installed, I have replacement springs from Crane Cams with a bit higher rated specs.
Custom Oil Pan
Doing a M2 install with a 250 is a challenge because you need a rear sump pan, there never was a rear sump pan and until recently there were no stock or custom style pans for sale (now only a fairly expensive stock pan is available). This leaves me cutting up my one and only oil pan and making it into a rear sump pan, I put this off a long time because if I messed up I would be scouring the junkyards looking for a replacement. Also I was concerned with my own welding skills to make something leak-free.
Finally I had to just make the cut and hope for the best, the first cut is the hardest.
A bit of thought went into building the pan and I will say I am pretty proud of the results, made a bit higher volume pan also baffled it inside, added a new relocated dipstick and extended the oil pick-up tube to the rear and finally, a bit of epoxy was used to make sure the seams were sealed, just in case.
The camshaft is from Howard’s Cams, as stated earlier, it has an advertised duration of 275/275, and a lift of .470/.470 also it is ground with 4 degrees of advance.
The timing set selected is the earlier stock version (’69-’72) because Ford kept retarding the timing to reduce emissions and killing power. There are no aftermarket timing sets for the 250.
I chose a set of ’65 Galaxie 390 hydraulic lifters because they are an exact fit for the 250, I also chose ’65 Galaxie 390 solid lifter pushrods, the reason for the seeming mismatch is the solid lifter cars had adjustable rocker arms so they are the cup and ball style, 250 only had ball and ball push rods for hydraulic lifters and non-adjustable rockers, I used a set of adjustable rockers ($10 from local scrap yard) from an early (’60-’63) solid lifter 144-170 because it allows you to pre-load the lifters without having to get a custom length pushrod made (the 390 pushrods are the same length as 250 pushrods) it also gives you adjustability when doing machine work like decking and head milling.
You have already read that I had ’77+ 1.75″ intake valves installed and the stock 1.38″ exhaust valves (Ford never changed the exhaust valve size from ’65-’80) some have installed 144 intake valves (1.467″) as exhaust valves, I would have attempted this but there is a danger of cutting into the water jacket on cylinder #1 and I did not think it was worth the risk. To make the engine a bit more durable hardened exhaust seats were added so unleaded gas would be safe to run, the exhaust valve seats needed to be replaced anyway because of pitting (remember this head was from rusted stuck ’72 200 with unknown miles)
Exhaust Header Issues
One issue that comes up with the 250 is a header, there are few to no options that fit. The issue is, while many headers will bolt onto the head they will not clear the starter because the 250 has a different location than the majority of the small sixes for the starter, it mounts low next to the oil pan while all the others mount up next to the block (the exception is 200s from the ’80s also have a low mount starter)
I purchased a Pacemaker header many years ago, so initially I tried to fit it and determined without major mods it was not going to work so I bought a new stainless header off of eBay, while it was closer to fitting it still would not clear the starter.
My first thought was to go back to the Pacemaker because I could at least weld on it, I did some modifications to it and beat the thunder out of it, it fit but I wasn’t happy about it.
I decided to go back to the stainless header and work out a different solution which ended up being a set of 3/4″ aluminum spacers I made out of some plate aluminum.
they bolt on with some long studs and give the header the needed clearance at the starter.
I have some modification left to do to the down pipes but it worked out well, not sure it would have if I still had shock towers but it fits my Comet fine.
The A/C compressor will still be an issue to get mounted but I have an idea of how to get that done and will post in the appropriate section when I get to that point.
In the late ’80s after I had finished the first modifications on the Comet I knew I needed an overdrive to make the car more street-friendly, running down the highway at anything over 55MPH was nearly impossible, but then again, at the time 55 was it on the highway anyway. Certainly even into the early ’90s swapping a T-5 into the car was cost-prohibitive and adapter kits were pretty much not around at least as far as I knew, that is all different in 2018. Even though I changed the rear end gearing from 4.11 to 3.73 and put a larger diameter tire on the car, overall those are fairly low numbers so I will benefit greatly having the overdrive.
I waited for a good deal on a T-5 of the few times Craig’s List worked for me, I saw an ad for a Ford Thunderbird Turbo Coupe T5 for sale that came with a “parts” T5 as well for, IIRC, $200, I called or emailed and found out they were available and went 70 miles and bought them and brought them home.
The parts transmission was a ’98 Mustang V6 T-5. If you are wondering why it was a parts transmission is because the guy had bought it to fix the 4 cylinder T-5 because he had accidentally knocked a hole in the bottom of the case and was going to use the V6 T-5 case and put the guts out of the T-Bird T-5 into it, I wasn’t interested in the 4 cylinder transmission (too low geared 1st and 5th) at all only the V6 one, which I opened up, inspected it and installed new seals into, a super clean transmission with no sign of wear or abuse inside, something one might not get with a V8 transmission.
With a good transmission, I needed a way to connect it to the engine, my original plan was to install a V8 bell housing, which involves replacing the input shaft and bearing retainer with shorter V8 parts. Now to explain why that did not happen because that is the way most people who install a T-5 on a 250 do it, my first priority is to maintain my budget, when I started looking for a V8 bell housing all that I found were around $150-$200 but I found I could buy the V6 bell for $50. The ’98 V6 motor also has the SBF bell housing pattern, they will interchange.
The other issue I encountered is the V8 bell is designed for 152 tooth flywheel and the V6 uses a larger 168 tooth flywheel, this is actually an advantage for someone putting a T-5 on a 250, or any other Ford small six, the Ford inline 6 motors are internally balanced and use a zero balanced flywheel, V8s, on the other hand, have a couple of different balances but not zero, you can buy a 152 tooth flywheel with bolt-on weights but they are expensive but a 2002 3.8L V6 flywheel is zero balance and cheap (I believe a Ford 300 I6 flywheel will work as well) The only issue is the shifter will come up about an inch further back inside the car, which was fine on my car, it moves the shifter far enough back to almost miss the cross brace in the transmission tunnel, I ended up only needing the remove half of it and reinforcing it.
I also addressed the speedometer drive gear while I had it apart I put a 6 tooth black gear on which when matched to a 17 tooth cable gear to work with 3.73 and lower rear gears my speedometer should be close to accurate.
With the transmission back together I addressed the shifter, I read that one of the biggest problems with the T5 is a poorly designed shifter, so I opted for a short throw shifter with adjustable positive stops.
I am using the shift lever from my original Hurst Indy H, I just cut it off the 3-speed set-up and drilled new holes because I did not like the shift lever that came with the replacement shifter, I thought it looked too modern for my Comet.
Flywheel, Clutch & Pressure Plate
I really have not related much into my choices on a flywheel besides being cheaper, I guess to help everyone understand why I chose a ’02 flywheel and not a ’98 one, Ford had a tendency to switch the V6 back and forth between a zero balance and a weighted flywheel (I can’t remember what the weight was) in 2000, or so, they switched all the V6s to a zero balance so, to be safe, I chose the latter flywheel. The flywheel is not a perfect fit for the 250 because the 2002 flywheel uses metric bolts where the 250 bolts are SAE, they are really close to the same size, you could almost force the SAE bolts into the holes, so I just reamed the holes out larger on the flywheel, it won’t hurt anything because the flywheel is centered by the middle hub, not the bolt holes. The flywheel was also balanced with the rest of the rotating assembly at the machine shop.
I went back to ’98 Mustang for the clutch however, just to make sure it matched my transmission, it really doesn’t matter because they all had the same part number on RockAuto. ARP flywheel and pressure plate bolts were used.
The ’98 T-5 bell housing was set-up for a cable clutch but I decided I wanted to have a hydraulic clutch, I also did not want to pay for an expensive kit so I made my own from off-the-shelf hydraulic clutch set-ups, basically, the goal was to find a slave cylinder with the proper stroke and match a master cylinder to that, the slave chosen was for a ’92 Isuzu Rodeo and the master is for an ’86 Toyota Landcruiser, I made a custom bracket to attach the master cylinder pushrod to my Comet clutch pedal and mounted the clutch master on the firewall next to the brake master cylinder.
An AN-3, 36″ stainless braided hydraulic line connects the master to the slave mounted on the bell housing. I fabricated a custom mount for the slave cylinder that includes an access cover, I had to cut the end of the clutch arm off to keep it inside the cover and make a couple of modifications to the bell housing itself.
The last thing to fabricate was the rear mount for the T-5, I used the original mount holes in the frame and made a bracket out of 1/2″ steel and used the stock T-5 isolator and a piece of the Mustang transmission mount that came with the transmission.
I am not super happy with the mount and may change it down the road, my biggest complaint is how low it hangs below the car. I am considering building one that uses chassis mount bushings, but that is future modifications if needed.
Not really too much to say about the driveshaft, it is an aluminum stock unit out of an ’09 Crown Vic Police car. The ’64 Comet and the Crown Vic both have the same wheelbase, 114″, so the driveshaft is almost a perfect fit. To keep from having the expense of shortening the driveshaft I had to scoot the motor forward 1/4″ and the rear back 1/2″ or so, easy to do on the back just a matter of adjusting the link bars, in front I had to modify my motor mounts a little.
The yoke on the Crown Vic driveshaft will not fit into the T-5, but the yoke on my original driveshaft will (yoke on original shaft is the correct size for a top loader 3 speed) A MOOG 448 conversion U-joint adapts the aluminum driveshaft to the top loader yoke.
Beginning Final Assembly
I am not fully sure how to continue this page because even though some of the earlier things are not finished the final assembly has begun, I think it best to just start a chronological post at this point, I will pick up on a few things I may not have even mentioned anywhere else yet, that does not mean they are not planned I have just forgot to tell everyone, also if something is double posted here I apologize.
With almost everything complete on the short block I decided it was time to get the engine off the stand and install the flywheel, clutch, and pressure plate followed by the transmission.
The flywheel and pressure plate were both installed with a set ARP bolts.
Actually the first time this has all been assembled, some things went on during mock-up but never all of this, the transmission and bell housing slipped right into place and bolted on like factory even if there was 20 years difference in the dates they were made, the 250 shines in this respect amongst all the other small Ford sixes, no adapters required for a T-5.
After a little ill-prepared work, the engine and transmission are installed for the final time (hopefully).
Along with the engine and transmission I got the driveshaft installed so for the first time the running gear is complete from front to back. Working about a half a day on it I got the speedometer gear changed on the cable, installed and routed up into the car, the hydraulic clutch hooked up, filled and bled at which point I recruited my wife to push the clutch pedal as I laid under the car and watched the slave push the release bearing disengaging the clutch, it all worked as planned.
At this point I still need to get my work done on the custom intake adapter pattern and get it cast, the head will come back off (it is bolted on now with no head gasket anyway, so the intake can be finished up plus I need to switch out the valve springs. This will allow me to get some wiring started on the car while I am working through all of that.
The engine is fully assembled now, I added a single one barrel carb just to get it started so I could do the cam break-in mainly and just test all the systems overall.
The only real issue I had starting it the first time was the connection between the distributor and ICM was not making connection, I removed the weather-tech style connector and replaced it with 3 spade connectors, rechecked that the distributor was not 180° out, went through and redid the initial valve lifter preload, reassembled everything and it fired right up.
I have rebuilt engines before but this was the first time I did a cam break-in in this way, usually would just drive the car, but cam manufacturer recommends 10 minutes at 2,500 RPM followed by 10 minutes off and a second 10 minutes at 2,500 RPM, I broke the fan belt about 2 minutes in to the second run so I had to postpone the final 10 minutes for a day because I had to go buy new fan belts.
After the final cam break-in was finished I finally got to hear it idle and did a couple of quick revs, hopefully sometime I can get the header hooked up to the exhaust.
The cam gives it a little lope at idle so this is a smooth as it will probably idle, I think it will help to have the exhaust hooked up for it not to sound so much like a tractor.
The next day I started it up and ran a few tests before backing it out of the shed and turning it around.
Later that afternoon my wife shot a video of me taking a quick spin around the yard, the gas pedal is pretty stiff and the clutch released near the floor (I have since adjusted the clutch up some) so my driving is not the best, as I get used to it I get a little better but the carb is just temporary and the throttle cable is not aligned the best so that issue will be resolved eventually.
The Comet is really smooth and seems to have real potential on the power, inline sixes are torquey anyway. I was pulling out of the shed to turn it around again yesterday when I blipped the throttle just a bit too much (remember it is a little stiff) the car wanted to go faster than tires could give traction.
Those were left by all throttle, my foot was off the clutch already, in the picture the car is turned the other way from the black marks, I made those as I left to turn the car around.
Been a little while since I updated, and a few more videos to add. Mostly I have been working on getting the exhaust installed and running down places where stuff rubs that is not supposed too.
I think on any build where you d build so much custom parts and install things not originally on a car you will have a bugs to squash, I think so far I have done fairly good with few issues and no major ones yet, I guess the best video to post first is the long one where I run down all the mods on the Comet so far which ends Phase one of the build.
There are a few videos on YouTube you can watch but going to post here the last one I took with it running, the valves set correctly and most of the rattles addressed.
I also had a starter issue that you can see in the above video, I made a follow up video on fixing the issue, right now the car is running great.
…To be continued.