I managed to get my engine assembled this past weekend. The machine work done to this engine, and the small job machining required to do the things I wanted to do was extensive to say the least.
But, I digress. On to the title of the thread.
I have fitted this engine w/ a solid roller cam. No small feat in of itself, but again, not what this is about. It is related to it however, as the spring pressures the stock timing chain would've been exposed to concerned me. ( 420lbs open BTW)
I learned about the lack of other than stock timing chains long after the cam was ground, and shipped from Australia, otherwise, I would've just had the cam grinder modify the cam snout accordingly to accomodate a SBF timing gear. That would've been Nice, and easy.
But that's not the way I do things.
Seems I never, ever, ever do things Nice, and easy....... Seems I want to do things....... Rough.
( Did you like my Ike and Tina thingy there?)
Doing things "rough" means trying to drill a billet roller cam after it has been subjected to it's heat treat process.
The difference between a cam intended for a 250, and a small block ford is significant when it comes to trying to make the gear from the SBF fit the 250 cam. The first process involved turning the snout down to fit the SBF gear.
Fortunately, this cam was induction hardned, as opposed to a complete through harden that would've made the cam unmachinable. Turning the snout down was no problem, as t wasn't subjected to the same treatment the lobes and journals were.
Drilling the cam face for the dowel pin wan't so easy.
The closer to center, the softer the metal. Starting out w/ a small .125 bit drilled easy enough, but, as the bit got bigger the diameter got closer, and closer to the hardened outside radius of the journal. By the time we were at the finish drill size to accomodate the dowel, the bit was chattering, and groaning. Needless to say, it didn't work.
I bailed on that plan, and drilled two smaller .250 holes through the cam gear, into the cam face. I figured that two smaller dowels would be stronger than one big one anyway.
The stock thrust plate was too thin, so we had to make a new one. I believe that the thickness comes out to be .240, but my cam gear has a torrington bearing for a thrust washer, so different gears will probably make that measurement change.
This is where things get a little dodgy.
Does10's has already done this swap, and he chose to modify the SBF chain by removing one link and using a master link to put it back together. Originally, I tried the same path, but had a real problem trying to find a link to match the Dido brand chain that came in my Summit brand kit.
After about three days and a bazillion phone calls however, I found a source for the right chain that actually came as a complete piece. Turns out that a 69-78 Toyota Corrolla w/ a certain engine uses this chain. The source told me to just go to autozone, and ask the guy at the counter for a Melling 3Dr56 double roller chain.
Or he could just sell me one for 15 bucks.
I chose "B".
Additional modifications are required to the crank, and the crank gear after that. The SBF gear has a shoulder that is about .300. This shoulder makes the gear stand way off installed conventionally for that reason. Does10s just flipped the gear backwards. I chose to mill off the shoulder.
Either way, whether you flip the gear does10s style, or machine it off like I did, The crank still has t be turned an additional .050 to allow the gear to sit far enough back to line up properly.
It fits like stock after you go through all of the above. The chain is perfect, just loose enough to allow you to install it.
Now, about the crank gear. I'm also using a SBF harmonic balancer. Conveniently enough, it's about .300 longer than the 250 balancer, so machining the .300 off of the crank gear would've had to happen one way or the other in order for the balancer to fit anyway.
One last "required" modification is the keyway on the crank. It's way too short and does not extend rearward enough to safely secure the gear given that you have to move it back even further. I had my machinist extend the keyway the full length of the crank snout to be safe.
But, I digress. On to the title of the thread.
I have fitted this engine w/ a solid roller cam. No small feat in of itself, but again, not what this is about. It is related to it however, as the spring pressures the stock timing chain would've been exposed to concerned me. ( 420lbs open BTW)
I learned about the lack of other than stock timing chains long after the cam was ground, and shipped from Australia, otherwise, I would've just had the cam grinder modify the cam snout accordingly to accomodate a SBF timing gear. That would've been Nice, and easy.
But that's not the way I do things.
Seems I never, ever, ever do things Nice, and easy....... Seems I want to do things....... Rough.
( Did you like my Ike and Tina thingy there?)
Doing things "rough" means trying to drill a billet roller cam after it has been subjected to it's heat treat process.
The difference between a cam intended for a 250, and a small block ford is significant when it comes to trying to make the gear from the SBF fit the 250 cam. The first process involved turning the snout down to fit the SBF gear.
Fortunately, this cam was induction hardned, as opposed to a complete through harden that would've made the cam unmachinable. Turning the snout down was no problem, as t wasn't subjected to the same treatment the lobes and journals were.
Drilling the cam face for the dowel pin wan't so easy.
The closer to center, the softer the metal. Starting out w/ a small .125 bit drilled easy enough, but, as the bit got bigger the diameter got closer, and closer to the hardened outside radius of the journal. By the time we were at the finish drill size to accomodate the dowel, the bit was chattering, and groaning. Needless to say, it didn't work.
I bailed on that plan, and drilled two smaller .250 holes through the cam gear, into the cam face. I figured that two smaller dowels would be stronger than one big one anyway.
The stock thrust plate was too thin, so we had to make a new one. I believe that the thickness comes out to be .240, but my cam gear has a torrington bearing for a thrust washer, so different gears will probably make that measurement change.
This is where things get a little dodgy.
Does10's has already done this swap, and he chose to modify the SBF chain by removing one link and using a master link to put it back together. Originally, I tried the same path, but had a real problem trying to find a link to match the Dido brand chain that came in my Summit brand kit.
After about three days and a bazillion phone calls however, I found a source for the right chain that actually came as a complete piece. Turns out that a 69-78 Toyota Corrolla w/ a certain engine uses this chain. The source told me to just go to autozone, and ask the guy at the counter for a Melling 3Dr56 double roller chain.
Or he could just sell me one for 15 bucks.
I chose "B".
Additional modifications are required to the crank, and the crank gear after that. The SBF gear has a shoulder that is about .300. This shoulder makes the gear stand way off installed conventionally for that reason. Does10s just flipped the gear backwards. I chose to mill off the shoulder.
Either way, whether you flip the gear does10s style, or machine it off like I did, The crank still has t be turned an additional .050 to allow the gear to sit far enough back to line up properly.
It fits like stock after you go through all of the above. The chain is perfect, just loose enough to allow you to install it.
Now, about the crank gear. I'm also using a SBF harmonic balancer. Conveniently enough, it's about .300 longer than the 250 balancer, so machining the .300 off of the crank gear would've had to happen one way or the other in order for the balancer to fit anyway.
One last "required" modification is the keyway on the crank. It's way too short and does not extend rearward enough to safely secure the gear given that you have to move it back even further. I had my machinist extend the keyway the full length of the crank snout to be safe.