Author Topic: thunder conrods  (Read 732 times)

Offline RDfella

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thunder conrods
« on: 27.09. 2021 18:29 »
Hi,

before I try contacting Thunder engineering again re conrods for my GF (tried a couple of times before but never got a reply) has anyone used them? I ask because according to online comments, their BE bolts screw directly into the rod itself, and are only 5/16" dia with a waist of .24". Sounds a bit iffy to me.  Dunno if I'd trust that.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Online JulianS

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Re: thunder conrods
« Reply #1 on: 27.09. 2021 20:15 »
Fitted Thunder Engineering rids in my A10 10 over years ago,  thousands of miles done no issues. The bolts are 3/8 UNF.

More substantial than the R and R rods I replaced and also the correct length which the R and R rods were not.

Online KiwiGF

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Re: thunder conrods
« Reply #2 on: 27.09. 2021 20:37 »
Hi,

before I try contacting Thunder engineering again re conrods for my GF (tried a couple of times before but never got a reply) has anyone used them? I ask because according to online comments, their BE bolts screw directly into the rod itself, and are only 5/16" dia with a waist of .24". Sounds a bit iffy to me.  Dunno if I'd trust that.

When I bought and fitted them (small journal) some 10 years ago now they were identical to the SRM rods, which was not surprising as they were SRM’s (recently) ex supplier of rods. I can’t remember the bolt diameter by what Julian said sounds right to me. It would be very surprising if the design had been changed since then.

I guess the bolts can be waisted down to the root diameter of their thread without becoming a source of weakness? It’s common to see highly stressed bolts with threads with an OD bigger than the shaft for that reason I guess.  Anyway I trust Thunder to have got it right, they have plenty of race engine experience.

They are works of art, shame to hide them in the cases 😏

New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts

Online berger

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Re: thunder conrods
« Reply #3 on: 27.09. 2021 22:52 »
one of the two for the berger build, 3/8ths bolts

Online KiwiGF

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Re: thunder conrods
« Reply #4 on: 28.09. 2021 01:50 »
one of the two for the berger build, 3/8ths bolts

So the bolts are threaded into the rods, but there is lots of thread length and engagement, maybe 3x the thread diameter......I guess this is possible because of the extra thickness of metal around the shells compared to std rods.
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts

Offline Swarfcut

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Re: thunder conrods
« Reply #5 on: 28.09. 2021 07:56 »
 RD Are you sure about this? If memory serves, this bike defied all logic regarding the lubrication system and was consigned to the dark side of the shed. What's changed?....Lottery win, windfall, even a win on the 4.20 at Newbury? No, I reckon with you buoyed with the success of the V twin, this bike will stand no chance of being defiant and be dragged kicking and screaming back to life.

 Swarfy

Online JulianS

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Re: thunder conrods
« Reply #6 on: 28.09. 2021 08:58 »
The fitting instructions which came with the Thunder rods.

One rod has the lubrication hole drilled, unlike the R and R.

Online groily

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Re: thunder conrods
« Reply #7 on: 28.09. 2021 09:00 »
Haven't any experience of the BSA version, but have been running Thunder rods in a reasonably hi-spec 650 AMC motor for about 20K km now, and very pleased. Pretty well bullet-proof I'd say. Over 40ft lbs 'n all to do 'em up. The AMCs have (3/8) bolts direct into the upper shoulders. (Originals had studs, threaded and cross-pinned into trunnions in eyes on the upper halves.)
Given the amount of thread depth and the recognised quality of their stuff, I'd be amazed if there was a problem on the beesa equivalent.
Here are my spare AMC ones for the next project if I ever get there.
Bill

Online RichardL

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Re: thunder conrods
« Reply #8 on: 28.09. 2021 12:19 »
one of the two for the berger build, 3/8ths bolts

So the bolts are threaded into the rods, but there is lots of thread length and engagement, maybe 3x the thread diameter......I guess this is possible because of the extra thickness of metal around the shells compared to std rods.

I, too, have Thunder rods via SRM, in turn via a machine shop that offered them as payoff for sloppy work. Bolts are from ARC. I think we could add to the threads issue that the forged billets are not putty. I was surprised when they arrived without small-end bearings.(edit: And, I should add, "by design.") Mine did not have a hole in the left-side rod, so I drilled my own.

Richard L.

Offline RDfella

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Re: thunder conrods
« Reply #9 on: 28.09. 2021 13:46 »
Thanks everyone for the input.
Nice to see the actual bolts - thanks Bergs. Must say 3/8" dia is more like it than an undercut 5/16" - maybe the ones the guy on the internet was referring to were RR or someone else's? I'd have expected the bolts to be UNC (or metric coarse) as they appear to be screwed directly into the alloy with no steel insert in the rod - but then again the coarser the thread the weaker the bolt due to reduced core diameter.
Swarfy - yep, the GF was another case of grief. Reckon my son's about right concerning my karma. However, the elusive lubrication problem was solved by a suggestion from a forum member (forget whom now). Despite oil pump and crankcase and gasket holes all lining up, a gasket with bigger oil holes was the secret. Doesn't make sense, but it worked. That bike has been on the road a while now, but old, mis-matched conrods worry me. I don't ride like an idiot, but I do like to blast through the gears to enjoy an engine. At present I'm loathe to do that. Also, there's more vibration from mid revs up than I like, so new rods and a re-balance over the winter is the plan, now that the vee twin is finally finished. Trying to resolve seemingly insurmountable problems with the latter's starter motor was not only perplexing but took up around 6 mths of my time.
 
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Online berger

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Re: thunder conrods
« Reply #10 on: 28.09. 2021 16:49 »
i really give my bike some thrash many a time 5000+ rpm in the first 2 gears and the rods are at least 60 years old. ---------i will let you know when one lets go if i'm still here and on the beer  *beer* *whistle*