Hirth Cranks

Discussion of 4-Cam Type 547 engines (and all the Fuhrmann racing variants) and cars that powered them.
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John Clarke
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Hirth Cranks

#1 Post by John Clarke » Fri Jan 21, 2022 4:23 pm

Are there any close up Pics of the Hirth Roller Bearing Crankshaft used in the 4 Cam Engines? showing the separate parts and the method of assembly.
Did they all have Hirths ? I know many were converted to Plain Bearings. Just interested.
Cheers Jay
 

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John Brooks
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Re: Hirth Cranks

#2 Post by John Brooks » Fri Jan 21, 2022 5:18 pm

John

You need a 4 can manual to see them easily, The crank is in sections with an bolt through the rod journal. Its been 50 years but you start at the big end and stack the roller bearings into the rod journal, then torque it and on to the next one. Each throw is indexed in to a spline and they are a pain with lots of individual parts. Probably Jacques or someone doing them there can send you a photo.
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Jacques Lefriant
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Re: Hirth Cranks

#3 Post by Jacques Lefriant » Fri Jan 21, 2022 8:17 pm

Hi
the Carrera book by Sprenger shows the 4-Cam versions has pictures

the total for 547 engines is 774 the 692/0 29 total 4-Cam 1381 so more than half were initially Roller. Converting to PB has been done since repair is questionable and new is exorbitant i am having PB cranks made that utilize the RB flywheel and crank gear to make the conversion easier.
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Jeff Adams
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Re: Hirth Cranks

#4 Post by Jeff Adams » Fri Jan 21, 2022 10:18 pm

I took these pictures a few years ago for a customer to help show some of the roller cranks basics, and to show work in progress.
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Re: Hirth Cranks

#5 Post by bil brown » Fri Jan 21, 2022 10:42 pm

Thanks for the cool pics Jeff.....what a beautiful mechanical puzzle!
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Re: Hirth Cranks

#6 Post by Joris Koning » Sat Jan 22, 2022 1:24 am

John,

You might want to check the three part article I wrote for the magazine on roller cranks several years back.
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Re: Hirth Cranks

#7 Post by Jacques Lefriant » Sun Jan 23, 2022 8:16 pm

Hi Joris what issues?
 

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Martin Benade
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Re: Hirth Cranks

#8 Post by Martin Benade » Sun Jan 23, 2022 10:54 pm

I think all three were in 2012, I got lucky and stumbled across them. I am not sure if they are searchable, or that they will be in the future.
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Re: Hirth Cranks

#9 Post by Joris Koning » Mon Jan 24, 2022 1:51 am

Jacques Lefriant wrote:
Sun Jan 23, 2022 8:16 pm
Hi Joris what issues?
Hi Jacques, volume 36 issues 2, 3 and 4
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Re: Hirth Cranks

#10 Post by Harlan Halsey » Mon Jan 24, 2022 7:41 am

At one point Jim Wellington published a picture of a disassembled 547 roller crank with the note: 555 parts!
(At the time Jim charged about $300 to rebuild one. I watched him doing one for a while. Jim had the tools, the necessary supply of SKF rollers, and some spare parts. He rebuilt mine and it has run well since. Bill Doyle had access to Jim's parts, and also built good cranks. 20 years of running the MHAR shifting at 6500 RPM is the proof.)

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Re: Hirth Cranks

#11 Post by Martin Benade » Mon Jan 24, 2022 9:20 am

Besides the rollers, what parts are replaced or regroups?
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Re: Hirth Cranks

#12 Post by Harlan Halsey » Wed Jan 26, 2022 5:29 am

Jim replaced anything which was damaged, but mainly the rollers and roller cages. The roller cages wear thin between the rollers and ultimately let a roller go crosswise ending your fun.
The bearings are steel rods running on steel journals. No bearing shells. The rollers take up the space. SKF supplied the rollers fine size steps, maybe .001mm diameter steps. Each journal was assembled, and the clearance measured by rocking the small end. Too much rock, larger rollers. I think the rock spec is in the Carrer Guide. I recall Jim telling me that when SKF ceased supplying rollers, he bought the remaining stock. Anyway, he had a shelf of roller boxes, looked like 10 boxes high by 10 rows. Without such a selection you cannot properly rebuild a Hirth roller crank. The rollers wear faster than the surfaces so a new crank could often be rebuilt simply by replacing the rollers and cages. But the new parts got used up, and I don't know how Hirth rollers are rebuilt these days. Luckily, I had my cranks rebuilt by Jim or Billy back when the parts were available. New Carrera roller cranks went about 40,000 miles on the street, but much less racing if you redlined much above 6,000 RPM. I usually shifted at 6,000 with a couple of 6500 shifts. That was enough to pull all the Speedsters in the early days of vintage racing. But today, I think it would take 7500 to be competitive. I ran that GT coupe nearly every year from 1982 through 2000 at the MHAR and once at Sears and had a lot of fun with it. Never any car trouble, but a lot of brake adjusting.

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Re: Hirth Cranks

#13 Post by Joris Koning » Wed Jan 26, 2022 6:27 am

Roller availability appears to be one of the main issues today. Jeff and Jacques are the ones to comment on this. I have no idea if any of them has ever looked to switching away from metric rollers should US sized ones be available and if these could be used with some modifications to say cages etc. From what I have been told Jim's old stock that now belongs to someone else is thin in rollers. Curious what Capricorn and Croswaith are doing
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Re: Hirth Cranks

#14 Post by Jacques Lefriant » Wed Jan 26, 2022 4:44 pm

Hi Joris
The short answer is convert to Plain Bearing.
i have enough rollers in standard and oversize's to freshen all the cranks we want. As you are aware Carrillo can supply rods and the size can be adjusted. Cages and outer races can be made easily. Journal repair is what i consider to be the major issue. Wellingtons's sleeving fix is far from ideal. Capricorn has made a few cranks and Croswaite and Gardner can also. If money is no object they can be made with better steel and ceramic rollers could be used which would be great. Also what i proposed in the past that a crank that presses together like the SPG made in small quantiles would be feasible. I am building a Hybrid crank that is basically identical to the 692/3A one that is used currentlu but the flywheel end is identical to the Hirth. this allows the reuse of the crank gear the ball thrust bearing and the superb application of the coupling for the flywheel. this makes the conversion easier and less costly than the current one.
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Re: Hirth Cranks

#15 Post by Rainer Cooney » Wed Jan 26, 2022 10:10 pm

Having rebuilt more than a couple of these crankshafts in the past I've never been fortunate enough to just replace the rollers. Most ,if not all of the time, one or more off the rod big end journals are spalled up. This is due to a number of factors. First the rod end motion is not purely rotational like the main bearings, they speed up and slow down at TDC & BDC and inertia eventually gets the better of this. The crank journal , coming in at 62 to 65 Rockwell C, is a bit less hard than the bearing rollers. Secondly this problem could be headed off at the pass if the crank didn't require special tooling for disassembly and inspection so consequentially they get driven until something happens. At that point everything but the crank itself needs to be replaced- bearing rollers, cages, rods ( outer races) and the crank journal needs to be dealt with. I have made new bearing races and main bearing outer races & purchased Carrillo rods. 6.5 X 6.5 rollers are still available from SKF but they prefer to sell assembled components so a secret handshake is required. They come "unsorted" but as received are very close to each other. I have in the past, before learning the secret handshake, purchased bearing rollers samples from various " suppliers" in the Far East or India. Luckily I have a good friend ex. Timken who offered to check these. As can be seen in the circular charts the two samples, center & left, aren't nearly as round as an original roller. Most of the time the spalling doesn't exceed .015" total and this can be ground off and used as is, crank heat treatment goes .045" deep or .090" total but by then it's too soft to use. In extreme cases the damaged journal needs to be induction hardened and for this the first question the heat treatment facility asks is " what is the material"? Shown is the test result from an MIT doctoral exam of the crank material and its composition. When finished as much of the assembly that can be made new is done and I sleep much better at night.
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