HS40 Rupp

dalpan

dalpan

#1
#1
I'm sure this question has been asked a hundred times. I'm rebuilding my original 1970 Rupp with parts from the original engine. Measuring the crankshaft up it looks like it's point .984, not good. What's my options? Are there new connecting rods available that are undersize?
I guess my dad was right I rode the crap out of this thing 20190620_184112.jpg
 
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Havasu Dave

Moderator
#2
#2
No, there are no removable bearings for it. What is your rod bearing diameter? The specifications as I'm sure you know are 1.0005 to 1.0010. In reality, you can clean it up and put it back together and it will live a long life. You could also try and find a NOS rod and see if the tighter tolerances would close the gap, or you could get a billet rod from an OHH 5.5 engine, as several of us have used those. I only recommend the later because this is a good engine, from an original, and vintage machine where the history is known, and it's worth it. Note the crank pin bore on it is advertised as 1.023, so it starts out, out of specification!

Not a bid deal! I'd get the billet rod just for the protection it affords. The weakest link on an HS 40 is the rod.

https://www.arcracing.com/6282-arc-billet-rod-tecumseh-5-5-ohv-3-484/

Having said that, you could spend some real money and have the crank journal welded and then turned down by an engine machinist.
 
dalpan

dalpan

#3
#3
The original connecting rod is split in two, and peaking thru the block. I have the HS40 from the 1971 snowblower, excellent shape. The connecting rod w/ calipers measures 1.004. I was thinking about the billet rods but was concerned with the clearance. Really want to keep this crank shaft. What's a ballpark figure for welding and regrinding?
Appreciate your feedback @Havasu Dave
15610779982345648451661174255264.jpg
 
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cfh

Well-Known Member
#4
#4
There is another (cheap) option. I had this same situation on a rupp HS40 motor. Took it to the machine shop and they said, "you know we can take just a tiny bit off the connecting rod mating surfaces, and it will run tight around that worn journal." So that's what they did.

First they smoothed the crankshaft journal. Mine had obvious wear. That took about 2 minutes of work. Then they did some light machining/metal removal to the connecting rod halves so when tightened, then were tighter around the crankshaft journal. That took another 2 minutes.

Cost was FREE (i think the guy felt sorry for me.) The motor actually is still running fine. I don't know what the life will be, but for as little as i use it, the engine seems to work fine.

I was pretty skeptical about the whole thing. But damn the motor was pretty worn out, i really didn't have much to loose. (It had other wear problems too.)

I know this isn't accepted practice, but it did seem to work. You can always go back in the future and have it done correctly, and install a new Arc connecting rod. Obviously don't do this modification to a brand new Arc connecting rod!
 
H

Havasu Dave

Moderator
#5
#5
To be clear, you can use the crankshaft as it is. These are not high performance applications with huge loads. You'd just need to remember what it is, and keep the RPM sane.

There are no clearance issues with the billet rod and the HS40.

I would only be guessing on welding and grinding costs. Probably $200 or less. And yes, you are right to want to keep that crank, because you could sell it to me right now for $150. :)
 
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cfh

Well-Known Member
#6
#6
I agree with Dave. as long as you don't go crazy with RPM you'll probably be fine. You may get some rod knock though if you don't get the connecting rod tighter against that worn crank journal. And that in turn will make the journal wear worse, and possibly throw the rod. That's why i took the approach of mod'ing a new stock connecting rod. Original Tecumseh connecting rods are cheap (less than $20), so mod'ing one really isn't an expensive idea.
 
dalpan

dalpan

#7
#7
Just curious was this crank exclusive to Rupp Roadster or are there other animals out there with this crank? $150, crazy my receipt for the Rupp back in 1970 was $350. I think I'll go with the ARC billet rod.
But @cfh , I might try the mod you were referring to. I have the connecting rod from the 71 engine to play with. Doesn't that change the stroke? I'm guessing probably not enough.
Again, thanks for the feedback....
 
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cfh

Well-Known Member
#8
#8
You’re only taking a few thousands off the mating surfaces on the connecting rod to get the play out. does it change the stroke? I guess. But it doesn’t seem to affect anything. I mean it is really just a lawnmower motor. You’re not taking this thing to the racetrack I assume, And you’re not driving it to Florida for winter vacation either

And yes the Rupp crankshaft is a bit different than a standard crank shaft. The area sticking out of the case is longer (3” versus 2.25”). And it uses a ball bearing side cover opposed to a bushing side cover. Do these things really make a big difference? No not really. But if you’re a hard-core collector, it’s an important detail.

Personally I don’t put a lot of weight into either of those two details. But some people really do think it’s important. I can still fit a torque converter drive assembly on a 2.25” exterior crank shaft length. And the ball bearing versus bushing thing doesn’t really seem to make a difference, at least to me. I mean it doesn’t make the motor faster (for the RPMs I’m turning which is under 3600 ). I guess it does last longer, but I’m never going to wear out any of my stuff. I’m no longer 10 years old, I have a job and a life. and riding minibikes only encompasses about an hour a week !
 
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Havasu Dave

Moderator
#9
#9
From what I gather, those longer cranks with the snap ring groove were Rupp only. @markus can tell you for sure, as he has done a lot of research on these, and has part numbers memorized, as well as drawings. (I have saved those for modification of later cranks to roller bearing PTOs)

@cfh that modification to the rod sounds pretty good to me. I'd use the same argument; they are not high performance engines. With no oil pump, and the benign RPM realm these run in, a little extra gap isn't going to hurt. I've run them with similar issues as dalpan has with this, with no noise.

So why not see if that extra rod can come down a few thousandths, then have them bore the bearing surface to specification. I'd still probably go with a billet on that worn journal, because I know it works- even with a high RPM engine. But I like cfh's idea.
 
markus

markus

Well-Known Member
#10
#10
Havasu Dave said:
To be clear, you can use the crankshaft as it is. These are not high performance applications with huge loads. You'd just need to remember what it is, and keep the RPM sane.

There are no clearance issues with the billet rod and the HS40.

I would only be guessing on welding and grinding costs. Probably $200 or less. And yes, you are right to want to keep that crank, because you could sell it to me right now for $150. :)
Click to expand...

I have one still in the lower .99+" range on the rod journal if you really need one?
 
delray

delray

Well-Known Member
#11
#11
dalpan said:
I'm sure this question has been asked a hundred times. I'm rebuilding my original 1970 Rupp with parts from the original engine. Measuring the crankshaft up it looks like it's point .984, not good. What's my options? Are there new connecting rods available that are undersize?
I guess my dad was right I rode the crap out of this thing View attachment 245941
Click to expand...
.984 not good , i'm sure it's little egg shape too. if you feel you can't use that crank because of the wear damage. i do have a guy here in wis that you can send your crank to and have repaired. i'm in the process of having him reweld a new crank journal and regrinding it from a 1.938 to a 2.00 stroke and the cost was $75 without tax and to have him ship it back to me. i did make the journey to drop it off to him(2hr+ drive) and see the process setup on how he does it. (very cool)
for your answer about rupps only having that style crank? i have not found any other engine yet with a long 3inch and bearing crank yet. maybe somebody else has? I have found 3inch cranks with bushings and i have found some hs-engines with bearing cranks but they have been real short for single belt pulley or with standard length. now for the newer tecumseh stuff for example ohh motors they do make a 3inch crank(actually 2 7/8+ long) and they are setup for bearing too. but they are much larger bearings then the rupp hs-40 cranks. also found some newer italy made tecumseh flatheads that use the rupp style cranks too,but they too look to be shorter shafts. all electronic ignition,still won't work.
if your keeping the governor on there is one other option you can use for a rod replacement. the newer ohh stock rods are 10x times better then a stock hs-rods are. i have been running a ohh motor without the governor and it pulls a easy 4700 rpm's and the rod seems to be holding very well for the last 3+ years. i now it's not a practice to run a engine without a governor on. it's been for me a test bed to see how well this engine holds up to all the other mods that i have done to it also.
here is a picture to show the difference between the two. top hs-rod /botom ohh-rod

billet is really the way to go...…..they never break. even at 8000+ rpm's
 
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Havasu Dave

Moderator
#12
#12
Delray meant bearing bore, not stroke. ;) I say that, because dalpan asked if modifying the rod would affect stroke. It will not in this context dalpan.

Delray, does that Wiseco come out to the same height? Do you know where to get those or a suitable substitute?
 
delray

delray

Well-Known Member
#13
#13
yes dave,crank journal can be ground to stock dem's and yes I am stroking my crank. that didn't sound right...lol
dave I did post something in the past on my wiseco coming out of the hole about .020
here is a picture of it.

personal opinion only dave, but I have work with two different engines with the vintage wiseco piston and both tend to smoke. not sure why the rings don't like to seal good on both engines. one was on a aluminum bore and the other was on a nickel silicon carbide bore and both had the correct finish hone bore.
my hs-build engine is only running a aluminum bore with a newer style .020 over hs-40 piston and thinner rings and that seems to work very well. I still like to try a steel sleeve setup build on a flathead in the future with the newer thinner rings.
 
dalpan

dalpan

#14
#14
Where at in WI.? I am located in central WI. I would entertain the weld and regrind. My concern was finding someone to do it right.
Yes, it is egg shaped, .986 - .983.
 
delray

delray

Well-Known Member
#15
#15
central wi,well looks like he is in your back door. location marshfield. advance auto 1818 north central ave.
guy's name is bean. ph 715-384-0001
here has done couple other OldMiniBikes guys cranks too in the past. right now your on a 2 week turn around. he is busy with grinding cranks.
 
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