Crank swap possible?

[jayvee43]

Hi guys.
Just a taught. Can you bolt a 194R top end onto a 56R,52R, 191 R etc bottom end & be good to go ???? Or take the crank from any of the 68 mm stroke singles & install the crank into a 194R case, bolt on 194R top end & be good to go ??

I have a local scrap yard that has a hirth 292 and 338. would any of them fit my 300 crank replacement?

I see here that the Hirth 190r - 191r - 193r - and 54r - 54r1 - r2 - r3 - r4 are all measuring 68mm stroke.

Has anyone ever tryed a swap?

OR: Would I be able to just bolt in a 292 or a 338 using the same mounting brackets of a 300 into my 500 chassis?

I know its a lot of question guys, But I'm this close to a possible donor motor. Thanks for any info you can give me on the swap subject.

[Roy Teske]

Hi Jesse. I know the 190R head will work on the 54R. I believe the 55R has a different crank than the 54R. Bolting in a different engine would be trial and error I think. Sorry I can't be more helpful. I'm sure there is someone in the area who has experience with these old hirth engines. There is a fellow in Blind River , Ontario named Ski-Roule Pete who can probably answer most of your questions. Very nice to talk to him. He got me started 10 years ago. I have his phone number at home if you would like it. Roy.

[jayvee43]

Thanks Roy. I'll keep this in mind.

I have to talk to my scrapyard guy first. I'm thinking of taking the bracket and the clutch to go see him. Maybe I get lucky.

[Go Go Diablo]

Hmmm..... This can be a difficult question to answer. There are some similarities between Hirth motors. I'll try to explain what I know or might know.

The pistons, connecting rods, cylinders and cylinder heads are all pretty much the same on the 52R, 53R, 54R, 55R, 190R and 191R motors (all 300cc and come standard with a 75mm bore). There can be some differences in the intake ports of the head, but that would not effect the fit or use, just possible HP rating. With that, you should be able to swap all those parts. If you have a bad connecting rod and know someone who can split a crank, you can find usable connecting rods in these other motors.

I believe the crankcase of the 52R, 53R, 54R and 55R motors are all the same. However, the crankshaft designs are different. So if you found a motor other than the special 54R with the 24mm tapered output shaft, the internals may be the same but your clutch won't fit. That does not mean a clutch could not be modified to fit however. The crankcase of a 190R and 191R I believe are the same too. Again, the 190R has the 24mm output shaft. I think the 191R has the 30mm shaft. The crank from a 190 series motor would not fit in the 50 series motors as the shafts and bearings are bigger.

The 56R is another motor that probably uses the same connecting rod, but the piston and head are 74mm. Could probably use this cylinder and piston on a 54R. I think the crankshaft would be similar but not have the small 24mm taper.

Same with the 192R (which is a 317cc and 77mm), the 193R (which is a 292cc and 74mm) and the 194R (which is a 338cc and 79.5mm). I think they use the same rod and cylinder, but have different size pistons and bores. Cranks may or may not be the same.

Seems all the Hirth motors have R designations. Like you mention Jesse, some are R1, R2, R3 and R4. Some of those designations refer to the factory placement of the head. In other words, which way they point the intake. Some of those designations also refer to the output shaft. So you could find a 54R1 for example and it won't have the 24mm tapered shaft. If you noticed, none of the Hirth manual start motors in Diablos have this 54R designation on the spec plate. Most other Hirth motors you see have it. My theory - Hirth made this motor specifically for Bolens and that small 24mm shaft is so special, that they did not put a 54R? designation on the spec plate.

What does this all mean? You can probably find parts to fix your motor easily if you have the ability to modify your clutch to match whatever crankshaft you end up with.

Hope that helps,

Bruce

[jayvee43]

OK, Here`s the (million dollar question)

I had time today to inspect my engine rebuild. I removed the cylinder head to look down the cylinder and look for possible signs of scores, or what not. Remember my engine was covered in BROWN RUST at time of tear-down.

Not to make a long story, The short is this: I have a LOT of play in my connecting rod to crank bearing. So much so that I am able to turn the top of the piston a few degrees left and right with just a pull push of the fingers.

Simply put, the rod bearing is done and will not last.

SO! Now the QUESTION.

I have purchased a PLAN B engine at the Eganville swap meet a few months ago, it is a 190 R2E (300cc) And I am planing on taking its crank off, and getting the connecting rod and rod pin and rod bearing off of that and get it pressed onto my 54R engine (300cc).

CAN IT BE DONE

I am gonna do this myself if it can. Then document it. What do yous think.

Jesse

[Go Go Diablo]

Jesse,

It will be interesting to see your attempt. I believe your rods, rod bearings and crank pins should be the same between the motors. Years ago, I looked for someone to press my cranks apart and back together again with little luck. Tried locally with the guy at Midwest Crank. Simply put, he was just too busy to work on these old cranks. Tried the business that bores out my cylinders and rebuilds motors and they would not attempt it but had some good feedback on how I could try it, but I was trying to avoid that endeavor. One last try to a crank business up in Minnesota and when they told me the price with me supplying the parts, I about fell off my chair.

So with that, I gave it a try. Pressing it apart is the first challenge. I was told not to use a torch to heat and expand the crank halves as that would distort the crank. For the crank I was taking apart to reuse the parts, I wanted to make sure I did not press the bearing part of the pin through a crank half so as not to scratch it. So setting it up in a press to do that was a real challenge. It takes almost all of what my 12-ton press can give to break it loose. I've done it a few times now and when they pop, things fly all over. Coincidentally, I'm in the process of getting a jig made to make this a safer process.

The second challenge I had was putting it back together and getting the crank halves aligned. I easily put in about 10 hours putting it together and taking it back apart and putting it back together again. Checking runout, doing the math and making adjustments was making my head spin. A tip the Midwest Crank guy gave me was when you have the pin pressed fully in one half the crank, only press the second half of the crank on half way and then check runout. At this point, you can make small adjustments of runout by supporting one half and hitting the other with a lead hammer. When you think you have it, then press it on the rest of the way.

This repair was done to a 190R motor and it started up and ran smooth and is still out there running today.

DSC01778.JPG (165.17KiB)Viewed 11382 times

I look forward to hearing about your repair and learning from your experience.

Bruce

[jayvee43]

I like your "V" block bearings, I would like to steal the idea.

I figured, I have everything needed to press it out, and together again, I have a 20 ton press, I have V block and I have vernier and micro caliper gauges with magnetic base. All's I need is a 5lb Brass hammer. I studied the video on line and it looks doeable. I don't really have a choice, unless I can exchange a 54r for a 190r and only pay the shipping.

I'm not crazy about killing 2 vintage motors. Seems to me it would be easier if i could find a good donor motor bottom end.

keep you posted on that as well, probably won't do it until I got all the details in place.

[Go Go Diablo]

This fella has a 3 part video series. He makes it look easy. I sure did learn a few things and looking forward to trying another crank this summer.

http://www.youtube.com/watch?v=cIe7Pd-VNhs

[jayvee43]

Yes I agree, that is a very good explanation video series on how to successfully press a 2 stroke crank.

I am in the process of getting everything needed for the crank job.

I purchased my own press. They were on sale. (no more worrying about using the one at work) specially if i am looking at a possible 10 plus hours of fine-tuning the run out.

I decided I was gonna make a "V" block jig next, (I'm steeling your design Bruce!!!) so stay tuned for that.

I have added a couple pictures of the press and bearing separator. Only I have bought a too small a seperator.

It's OK, I will get a bigger one and have both sizes if I need the small one at some point.





Here I have a sample crank out of a 338cc The bearing is shot out of that one, but I will be using it as a mock-up to help me prepare for the actual cranks. It's gonna come in very handy.

[jayvee43]

OK, Been lucky enough to spend some time with the "crank shaft mission impossible"

I had to make me a JIG. The reason I need this is because the way the crankshaft is built. More like cast. Corect me if I'm wrong Bruce, or anybody that know different, but not all the crank halfs are the same. My 190r has a different crank cast than my 54r.

OK, my project needed a solid piece of steel. I got me some 1/2 inch steel. Then I taught it long and studied what is available out on the internet, nothing seemed to do for this type of crank. Anyways I needed to be able to seperate it cleanly since this "sample crank" is identical to the one in my "donor" motor.

Well, I'll let you guys look at my series of pictures, they will explain my solution. I hope.