Roper 3.7 tear down and rebuild

I am going to guess most have seen my other Roper thread. Since I am now an official Roper hoarder, I figure I'd fill you in on the next step in my descent into addiction. I decided to tear down the original 917.353750 saw, this is the one Roanoker sent me a flywheel for, since my existing flywheel is kinda low on fins and out of balance. Before I tore down this saw, I checked compression and it was 105. It seemed to run fine and pull well, but I guess it could do better for the next half century of its life with me. My plan is to replace the slug, and rings, crank seals, maybe bearings, find a new crank carrier, see if it will scream again and then go from there. I found a few more interesting issues of course in the tear down tonite following a wonderful week at work. (Not) Anyway, it is Friday and that means just 3 more working days til Monday. Well, Friday's over so just 2 more now.
The compression release valve was stuck, seemed it didn't completely close, but wasn't really open, it was stuck. I got it free but since I no longer trust it, I figure it should be replaced, so I'll be begging in the Swap thread for someone to bail me out.



There are 2 rings on this piston, but for some reason, the ring gaps are aligned instead of staggered as I would have expected based on automotive experience.







Dome of Piston, marked EXH for exhaust port location/orientation.



The piston actually looked very good for 40+ yrs of age, but maybe not a full 40 of use perhaps. "Front."



"Back"



The shiney stripes aren't wear, this is where the intake is so there is no contact, the stripe up the middle between the two shines is explained by the cylinder photos in the next post.

So here's some bore shots of the cylinder, I think it looks great.









Reeds looked fine



I found a bit of worrisome carnage on the edge of the tank, it was from a screw rattling loose from the drivecase carrier that then wedged under the flywheel, but it didn't seem to go all the way thru. I belive a dab of some RTV here will help, seems more flexible than JB weld.



So tomorrow I will re-join the 2 case halfs of the tank, will put RTV bead between them to seal the joint so the tank won't leak, and tear down the bottom end so I can check the bearings, they "feel" okay though.

So far, here are the original parts numbers I am aware of from Sears.

Rings--643A18
Piston--643A12 (but I don't think I need a piston)
Crank seals-8998H
Compression release valve--1579R

I'm not aware of a way to cross-reference these with any currently available parts, so I'd be glad to hear from anyone who can recommend a source. I have one lead but have not got a response from that ebay dealer as of yet.

So at this point I have a few questions for the forum--first off, is RTV the proper material to use as a sealer between the 2 case halves to seal the tank?
second--anyone have any sources for the above listed parts numbers, or perhaps have a compression release valve that is good rattling around? Also need to come up with the drivecase carrier for this, since I'm deciding to go all out on the rebuild, I suppose this part should be replaced as well, here is photo of that part. I believe I'm going to be getting some more PMs from Roanoker and perhaps another package coming my way after another Paypal transaction.......sorry to be such a black hole of need.





There may be others as I get further into this, but I promise I will be submitting tons of photos (chainsaw P**n--rhymes with "corn") as I go thru this.

have a needle in a haystack?!!!

well buddy here's the good news and the bad news...the roper built saws are good and torquey when running good. i had a 24" windsor with full comp on mine and it never bogged down! however the bad news is you might as well wipe your butt with those part numbers as finding new old stock parts is not even hard...ITS IMPOSSIBLE! i have never seen any on ebay or otherwise in the six years ive been working with these saws. lots of parts saws cheap on ebay except shipping costs add up. as far as your piston dilemma, i found homelite Super XL pistons work nicely in these saws which are internally copies of the homelite anyway. SXL rings should also work. just remeber the ring gaps always face the intake side of the cylinder. i found a crank seal that matched up with a part from work and so far they have worked. you can get it fixed sure enough but your're going to have to do your legwork to match parts up with non roper parts. i'll look for a spare decomp valve. i have some lower compression saws that i didn't have to use the decomp valve to fire it up with so a plug in its place is acceptable. they have a decent recoil so they don't exactly break your arm. may the force be with you!

RTV for a case sealant? I never use it myself. Any silicone based sealer and gasoline is a no no to me. I use Threebond. Same stuff under different names.........Yamabond......Hondabond.......Dirko.

I have also used a Permatex sealer that is resistant to gasoline. If in doubt read the back of the tube to see if it's resistant.

The old saw seems to be in good condition. Good luck with it.

I'll start looking around for the gasoline resistant case sealer you listed, starting with car parts places etc. I haven't heard of those particular products so don't have any experience with them but that's why I find this forum so helpful.

I never figured I'd find anything of the original parts numbers, but I figure it's handy to have the orig PNs as someone out there has a cross reference, or a dimensional equivalent etc. I'm digging around and of course will list current PNs and current suppliers when I come up with the parts.

go on down to your local mudercycle dealer and ask for a tube of yama honda kawi ultrabond 1194. i pay just under 15 bucks for a tube, but it is well worth it:msp_thumbup:

Seals and bearings are available at your local industrial parts dealer and auto parts stores.

On seals you need to know the shaft diameter, housing diameter, width, and style (single lip with garter spring is the most common for saw crankshafts).

Ball bearings are made to metric dimensions. Bore, outside diameter, and width with seal(s)/shield(s), and/or snap ring groove is necessary to cross over replacemnts.

Needle or roller bearings are same drill as ball bearings exept they are made to inch dimenions on made in the USA saws.

Look on the side of the bearing or seal for manufacturer name and number.

And now a problem............

67L36Driver said:

Seals and bearings are available at your local industrial parts dealer and auto parts stores.

On seals you need to know the shaft diameter, housing diameter, width, and style (single lip with garter spring is the most common for saw crankshafts).

Ball bearings are made to metric dimensions. Bore, outside diameter, and width with seal(s)/shield(s), and/or snap ring groove is necessary to cross over replacemnts.

Needle or roller bearings are same drill as ball bearings exept they are made to inch dimenions on made in the USA saws.

Look on the side of the bearing or seal for manufacturer name and number.

Click to expand...

I wasn't expecting loose needle bearings when I took the end cap off the connecting rod, but of course they all dropped into the case. I recognized the potential disaster of losing one or more of these so FELT I was being extremely careful in tipping them out onto a clean plywood work table. I counted 30 so felt good with the even number somehow, but a bit later while walking out of the garage to clean the case I saw one on the concrete floor. Great, so now 31. I didn't feel real happy at that point so reassembled the connecting rod on the crank journal with the needle bearings in place with some sticky grease. There was no play on this when I tested it prior to pulling the conn rod, but it has about 15-18 thousandths now. Everything was marked for orientation prior to disassembly, so the bearing cap is on the right way, etc. I can't explain the play in this. There could be a missing needle bearing, but that would not really account for the play. I've put U joint caps back on the trunnion that felt fine, then I notice the loose needle bearing that went walkabout. I spent 1 1/2 hours looking on hands and knees, with light held tangentially, with a magnet, I even eviscerated my tool box and went thru that in case the needle had stuck to a tool and hitchhiked into there. No joy.

So possibly 2 problems--Do you happen to know the count of the needle bearings for this saw? Any thoughts on why I would have this very noticeable large amount of play? I have been over this and it doesn't make sense.

Nice pictures. Thanks for sharing. I too have never seen piston ring stops lined up together. Kind of defeats the rings purpose, doesn't it?

When you get the rod in your hand (out of the saw). Put the cap on it and all the needles. Then you can tell if any are missing.

Mastermind said:

When you get the rod in your hand (out of the saw). Put the cap on it and all the needles. Then you can tell if any are missing.

Click to expand...

Yeah, there is a little space, it does seem another needle might just squeak in there, but I don't know how much the cap deforms on tightening it down. Some major Roper affectionado must know the count. (and hopefully have a remedy to bail me outta trouble)

Opihi59 said:

Yeah, there is a little space, it does seem another needle might just squeak in there, but I don't know how much the cap deforms on tightening it down. Some major Roper affectionado must know the count. (and hopefully have a remedy to bail me outta trouble)

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Maybe, just maybe XL12 needles are the same size. They're common as hell here.

You can fab a leakproof case gasket using a brown paper grocery bag. Just take your time and press the paper over the sides of the case to form the cutting outlines. A new razor blade and a pair of sharp scissors will make it quick and easy. If you have a paper punch for the bolt holes that will help too.

Ive seen too many scored cylinders on gasketless cases. Sometimes the sealer holds and sometimes it doesnt. Expansion rates are different for a magnesium case and an aluminum cylinder joint. I use a fine coating of loctite 515 or 518 over the brown paper gaskets that I make and have not had any issues with them.

I usually purchase gasket sheets from NAPA/redline and cut out what I need. It works well, and I am rather tedious and meticulous in making these. I have access to any type of scalpel blade I need. No worries thus far.

roostersgt said:

Nice pictures. Thanks for sharing. I too have never seen piston ring stops lined up together. Kind of defeats the rings purpose, doesn't it?

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If you buy rings from 'the Greek' on ebay, plan on notching the ends to fit around the locator pin. Use a 1/16" dia. swiss pattern file. You will gain a significant amout of compression going from .075"-.089" to .003"-.005" end gap.

I'm starting to come up with parts sources, Roanoker sent me a flywheel. I have been back and forth on PM with 67L36Driver and with the Greek on ebay seeking out ring options. I have done some research on crank seals by dimensions--Bore dia 0.875" and shaft size 0.625" and come up with 2 SKF seal number 712130 and 721503 and will see if I can now locate a source for a small handful of them. They are not as thick as I appear to need being 0.125" but they may be worth a try. I'll keep updating this thread with successes as well as failures as I know there is a Roper following out there.
I don't have a particular attraction to these Roper saws, it's just that this one belonged to my Father and I used it as a young adolescent and we're both approaching "vintage" or somewhere beyond. It does give me satisfaction to work this over and I really want to hear it fire up and annoy the neighbors. Then I'll find something to cut up with it.

Keep us updated. I really enjoy seeing a saw project come together, especially a challenging older one.

Opihi59 said:

There are 2 rings on this piston, but for some reason, the ring gaps are aligned instead of staggered as I would have expected based on automotive experience.

Click to expand...

I've wondered about this, too. My experience also comes from automotive.

My Makita 520i is a 50cc saw with only one ring....not two as I've seen on some Dolmar 111 pistons (the equivalent in design/model). My thinking says maybe the difference is with the two rings not being staggered is that none are oil retention rings. There is no oil in the case to keep out of the combustion chamber as with an automobile.

As well, atleast with Toyota pistons, there isn't a notch in the ring seat/groove so the rings can be staggered....or, consequently, have to be staggered.....whichever way it is.

And, lastly, maybe the notch on the saw piston negates the rings needing to be staggered being adequate in design for creating compression. On my Makita, the ring ends close up pretty tightly against the notch once installed in cylinder.

Just my thoughts. I'm no 2cycle expert.

The rings on the Roper (and many, many others) are pinned in one position. That is so the ring end won't end up snagging in the exhaust port or transfer port.

For the above reason end gap is typically .075"-.080" to clear a 1/16" dia. locator pin.

Conventional rings with a gap of .003"-008" can be notched with a 1/16" dia. swiss pattern file. (tiny little sucker) to clear the locator pin on the Roper (and Pioneer, Homie SXL etc.) piston.

Less ring end gap = more compression and less waste fuel

67L36Driver said:

The rings on the Roper (and many, many others) are pinned in one position. That is so the ring end won't end up snagging in the exhaust port or transfer port.

Click to expand...

Well, thanks for answering that. I'd just read about it another thread, too. So, much for my thinking....