Okay, I am extremely busy through Wed. Hopefully, I can finish up the complete tutorial by next weekend. However, in the meantime here is my version of the installation of the mainsprings and hammers.

Tools:

5/32" pin punch
1/4" pin punch
flathead screw driver (approx. 1/4" blade and 8" long - longer is fine)
bench vise OR several c-clamps
turnscrews

Parts:

mainsprings (2)
mainspring strain pins (2)
hammers/strikers (2)
hammer pins (2)

First, secure the screwdriver handle in the vise (or clamp it to the bench) with the blade oriented horizontally (this will be used as a lever, so keep the shaft/blade accessible).

Next, place the first mainspring into receiver as shown in photo and keep it in place by installing the mainspring strain pin.

Next, support the receiver upside down on the bench and compress the mainspring far enough for it to clear the hole for the sear spring/cocking bar pin (I used the 1/4" punch to press against the leaf of the spring, but many things could work including your thumb if strong enough).

Insert the 5/32" pin punch through the hole in the receiver for the sear spring/cocking bar pin and seat it into the center block on the receiver (see photo). The mainspring will now be pressing against the pin punch and you're halfway home.

Next, wedge the blade of the clamped driver in between the pin punch and the mainspring and rock the front of the receiver downward so that the driver - acting as a lever - further compresses the mainspring.

Place the hammer into position and with it's through-hole aligned, install the corresponding hammer pin. The 5/32" punch will now fall out.

*NOTE: try not to release pressure on the lever until the hammer pin is screwed down quite far (ideally, all the way - but half a turn shy will be secure enough not to bugger the threads).

Remember that the 5/32" pin punch is a near perfect fit, but 11/64" will probably fit a bit better. I would find the best fit before getting started, just in case a Crass model is a bit different in that way from a Lewis.

today I received a package from Numrich/Gun Parts Corp with 12 parts I had ordered from their Ithaca Crass page for my shotgun; unfortunately, only 3 of the parts fit, so now I have to send back the other 9... :(

Ah, fun isn't it? I went through my box of Ithaca parts and it was slim pickings for the Crass model, but I have a few. What are you still looking for?

And have you reviewed my earlier post on the mainspring install? Any questions on it?

For my shotgun, I am missing this part (or these parts) depicted in the following three (3) photos [these are all photos which others have already posted in this thread so far]:
http://i842.photobucket.com/albums/z...psc57cfea1.jpg
Al labeled those two parts as (48) Trip Spring and (49) Trip Pin

http://i842.photobucket.com/albums/z...psed04708f.jpg
http://i842.photobucket.com/albums/z...ps00a3df92.jpg

From the Gun Parts Corp - Crass Hammerless website, I thought that was part no. 1154850 - Cocking Bar Spring [PLEASE CORRECT ME IF I AM MISTAKEN], but regardless, the part I received did not fit as depicted in those three (3) photos, for it was too short to span the distance between the threaded hole and the smaller hole for the pin. I received a part like what Al showed, which is shorter than the other two photos with the (single, longer) part in place, as Jeff had initially posted. Additionally, I only received a single part, not two, i.e. I do not have a small diameter pin for that hole to retain the Barrel Locking Bolt...

Finally, can someone please explain the function of this part (these parts)?

For reference, all my parts look exactly like what Jeff Bonadurer initially posted to start this entire thread. Unfortunately, they differ from the shotgun and parts which Al had to create his pictorial tutorial...

In this photo (which looks like my shotgun), can anyone identify the part(s) circled in red and explain their function?
http://i842.photobucket.com/albums/z...psca08df0d.jpg
Or does anyone happen to have better photos of that part (those parts)?


Also, can someone tell me on what the ends of the sear springs are pressing (the portions circled in red) - those are the mainsprings, right?
http://i842.photobucket.com/albums/z...ps78a4bc8e.jpg


Finally, Al, yes, I studied what you posted about installing the mainsprings, and that shouldn't be any problem once I actually get to that step... I have to deal, however, with a few other issues (and missing parts) before I get to that point...

I will upload additional photos of my own Ithaca Crass and post them for reference

Bach, the parts you are referring to comprise the trip assembly. That is what keeps the toplever to the right and the locking bolt in its rear position until the locking lug on the barrel set trips out the pin upon closing the breech.

Apparently, the trip spring (leaf spring) on a Crass model is a bit longer than that found on a Lewis model, and what Numrich had listed under its Crass model parts for sale was a Lewis model spring. It makes sense, the longer spring for the Crass model, since I believe the Crass receiver to be a bit longer than the Lewis.

If Jeff can get you the overall length of his Crass model spring, you can attempt to contact Numrich. Hopefully they will be willing to go through their stock of "Crass model" trip springs looking for the longer one(s) to send to you as a replacement. As mentioned once before in this thread, I had given something like that a try with them before, to no avail. Probably worth a shot, though.

In the next two photos:

1) looks like something to do with the safety/trigger assembly.

2) yes, the front of the sear springs rest on the bend of the mainsprings. Those are the polished surfaces you have circled on each side.

***note: what Numrich seems to have listed as the cocking bar spring is actually the trip spring and has nothing to do with the cocking bar. There is no cocking bar spring. The cocking bar engages the toes in the the hammers directly and any spring force acting on the cocking bar is transferred from the mainsprings through the hammers. From Jeff's photos, the Crass model looks to be identical in this way to the Lewis.***

In the first picture the trigger guard was turned to the left. Your seeing the curved part of the trigger guard behind the second trigger. Here it is in its proper position and also swung to the right.

can you please elaborate exactly how that functions?

without that trip assembly part, I can visualize how the spring keeps rearward pressure on the barrel locking bolt (via the trip assembly pin located in the forward notch of the barrel locking bolt), but what I cannot visualize is how/where the locking lug on the barrel set trips out the pin (which pin?) upon closing the breech...?

I'm sure having that part would help...