Long Con rod, Short Piston

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Long Con rod, Short Piston

Post by Momus » Fri May 15, 2020 9:46 am

My understanding is the 'long' rod is coupled with a short piston.

The deck height shouldn't change.
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Re: rocker box cap screws

Post by minetymenace » Fri May 15, 2020 11:06 am

Momus wrote:My understanding is the 'long' rod is coupled with a short piston. The deck height shouldn't change.
That's one way of doing it, I guess due to piston availability, size or wind direction this is normally achieved on the B50 by using a half inch spacer under the barrel and long push rods.
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Re: rocker box cap screws

Post by Momus » Fri May 15, 2020 4:33 pm

How much longer is the rod -5/8"? :shock:

Long rod/short deck 92 mm piston
SAM_0513.JPG
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Re: rocker box cap screws

Post by beat » Fri May 15, 2020 8:50 pm

Momus wrote:
Fri May 15, 2020 4:33 pm
Long rod/short deck 92 mm piston
brand ??

beat

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Re: rocker box cap screws

Post by Momus » Sat May 16, 2020 9:30 am

beat wrote:
Fri May 15, 2020 8:50 pm
Momus wrote:
Fri May 15, 2020 4:33 pm
Long rod/short deck 92 mm piston
brand ??

beat
Wossner.
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Re: rocker box cap screws

Post by FGF » Sat May 16, 2020 10:40 am

some friend , an old BSA Goldstar user said me he used long carillo with a JE short skirt with no spacer.
ask to Ed , he knows.

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Re: rocker box cap screws

Post by beat » Sat May 16, 2020 9:56 pm

thanks moms, that I know it from my Goldie
DSCN1661.jpeg
on my Goldie
DSCN1653.jpeg
seams to be good stuff
beat

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Re: rocker box cap screws

Post by Momus » Sun May 17, 2020 7:19 pm

Similar piston for sure, machined differently re the ring placement, possibly from the same forging- does it have a forging number?

The con rod looks bulky for steel?
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Re: rocker box cap screws

Post by beat » Sun May 17, 2020 9:38 pm

can not check it for Numbers on it because it is inside the engine now, sorry.
the con rod ( it is steel ) is from ABSAF in the Nederlands, - no idea if there existing taller ones ?

what piston to liner clearance are you running ?

mine has 0.10 mm, so it is 89.90 size. ( 90.00 Bore )

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Re: rocker box cap screws

Post by Momus » Mon May 18, 2020 5:05 am

I'll run the new setup at .002 to 003" initially at least on 92.00 . Bore is Nicasil so the piston and cylinder follow each other around. Agree it is a bit hard to see up under the crown in an assembled engine.


We have gone completely off topic re the original posters question- and apologies to him for the hijack- so I will answer your question regarding the maximum stroke in a B50.

Using a 35 mm crank pin and a 42 mm rod bore bearing it looks like 106 mm is about it. -53mm on the arm is what I will aim for.

Beat, am I seeing case inserts for a main stud repitch in your photo? :cool:
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Re: rocker box cap screws

Post by beat » Tue May 19, 2020 8:13 pm

yes, the barrel for the Goldie with 90mm bore has encapsulated studs, so no way to set the spanner on them at the zylinder base as commonly.

means, long screws from the head top down to this case inserts.
DSCN1638.jpeg
DSCN1649.jpeg
DSCN1633.jpeg
crank with 102 mm stroke
Details are to see in the Topic " Off Topic " section, " Star "

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Re: rocker box cap screws

Post by Momus » Wed May 20, 2020 8:08 am

Good work with the studs and crank.

I think I mentioned back a bit that I made some studs for my B50 beast that give a deeper thread insertion -3D- and using M12 for a bit of security for a big engine with high comp.
I had another look at the stroke possibilities and it looks like 110 mm is feasible with the rod big end outer still being within the 162 mm ring of the crank and the piston not pulled down so far as to be a major problem with lack of skirt. Gives around 730cc :laugh
I have started on the crank construction so for the fun of it may try it with 110 stroke and 92 mm bore. Head is a weld up chamber squish thing and I may need a reverse dome piston to keep the compression ratio at around 13 to 14:1.

Did you make new mainshafts or reuse for your long crank?
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Re: rocker box cap screws

Post by twinshocker » Wed May 20, 2020 11:05 am

beat wrote:
Sat May 16, 2020 9:56 pm
thanks moms, that I know it from my Goldie

DSCN1661.jpeg
DSCN1653.jpeg

beat
Beat is that piston from Dottikon ?

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Re: Long Con rod, Short Piston

Post by beat » Wed May 20, 2020 8:51 pm

Momus wrote:
Wed May 20, 2020 8:08 am
Did you make new mainshafts or reuse for your long crank?
Got the parts for the crank from ABSAF, mainshafts are made for metric bearings. crank balanced for the Wössner piston here in my country at Gerhard racing in Frauenfeld.


twinshocker wrote:
Wed May 20, 2020 11:05 am
is that piston from Dottikon ?
yes shocker, it is from the British bike doctor. :grin:

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Re: Long Con rod, Short Piston

Post by beat » Wed May 20, 2020 8:57 pm

Momus wrote:
Wed May 20, 2020 8:08 am
it looks like 110 mm is feasible
spoke with the doctor today: 102 mm is the max he will go, gives 678 ccm. if I am right.
all this should go in to a B25 case,,,,,,,,,,
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Re: Long Con rod, Short Piston

Post by Momus » Thu May 21, 2020 5:57 am

It's sometimes said it is best to get the opinions of 3 Drs. before operating.
Dr Allan Clews is reported in the Rolling Thunder CCM book as having built 104 mm cranks, possibly for a trials sidecar.
So you have 90, 100 from PES, 102, 104 and my surmising with the verniers and a card board con rod mock-up of 110.

I was a little surprised to find hard metric bearings for the B50 mains in a 25/62/17 size. Would have bet on 1" -25.4 for the shaft.
I am cutting some 4140 round into slices for the wheels and will try some ordinary case hardening steel for the shafts. They obviously need to be hard but compared to a gearbox shaft with a smaller diameter and a torque multiplication the twisting loads are not too high. We'll see.
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Re: Long Con rod, Short Piston

Post by koncretekid » Thu May 21, 2020 4:48 pm

I'm running my 92mm bore x 90mm stroke @ 599cc in a 650cc class. Sure would be nice to get a 97mm stroke crank to get to 645cc. In 2018,I missed the SCTA speed record by .17 mph (149.99 mph on a 150.164 mph record). Last year the salt was soft, so I didn't make a full throttle run. This year, I can't even get down to the States until at least June 21st, and even then, we don't know if the event will be run.
Tom
P.S. The long rod is 6-1/2" long, the JE piston I use still requires a 1/4" spacer. This combination will fit in a standard B50 frame, as well.
life's uncertain - go fast now

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Re: Long Con rod, Short Piston

Post by beat » Thu May 21, 2020 8:56 pm

Momus wrote:
Thu May 21, 2020 5:57 am
It's sometimes said it is best to get the opinions of 3 Drs. before operating.
:lol: :lol: :laugh :laugh :lol: :lol:

well, my Doc has the 102 on the shelf, with 92 nikasil barrel and Wössner piston, plus modified B25 cases as well.....
I have seen those 678 ccm bikes running. <216

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Re: Long Con rod, Short Piston

Post by Momus » Sat May 30, 2020 1:47 pm

678 should be like a steam engine :thumb
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Re: Long Con rod, Short Piston

Post by Momus » Sat May 30, 2020 1:53 pm

koncretekid wrote:
Thu May 21, 2020 4:48 pm
I'm running my 92mm bore x 90mm stroke @ 599cc in a 650cc class. Sure would be nice to get a 97mm stroke crank to get to 645cc. In 2018,I missed the SCTA speed record by .17 mph (149.99 mph on a 150.164 mph record). Last year the salt was soft, so I didn't make a full throttle run. This year, I can't even get down to the States until at least June 21st, and even then, we don't know if the event will be run.
Tom
P.S. The long rod is 6-1/2" long, the JE piston I use still requires a 1/4" spacer. This combination will fit in a standard B50 frame, as well.
JE pistons are a good, conservative production if the B50 items I've seen are representative
SAM_0072.JPG
.

The 2 ring personalised short cut stuff gets a bit hairy.

Got 'em with the pin bore going through the entire oil ring land for proper strokers.
If you love it, lube it.

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