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Posted
Hi all,
 
I have an 840 kit set up & am getting ready to install it in one of my 4th gen. spare engines.
 
Has anybody out there have any info. on the jetting for the Dynamo Humm used in there kit engines ? ? ?  Be nice to have some sort of starting point.
 
 Bike will have full TBR race exhaust, & of course a K&N filter.
 
Thanks --------------- Josh
  • Member Contributer
Posted

Sounds like an interesting project. You may need to set up the hot tub time machine to get that info, I haven't seen one installed in about 15 years.

 

Is this an nos kit, or are they back in business?

 

  • Like 1
Posted

No, they are not back in business.  It's a kit I bought +-15 years ago.  The specs supplied by the piston mfg. were wrong, so the block was bored too much and had to be scraped.  I recently came across 2 engines, so I'm going for it.  The set up has been polished & balanced.

  • Like 1
  • Member Contributer
Posted

I used to & may still have the contact email for the guy that ran Dynamo Hum. Unfortunately I'm in the middle of the Mediterranean at the mo literally & won't be home until Monday. I'll try to dig it up & see if it still works & if he is still with us & has any details for you.  

Posted

That would be mind boggling ! ! !

 

THANKS

  • Member Contributer
Posted

Brian Law at Dynamo Humm, I think it was dyno@sympatico.ca but that's long gone. You can probably dig him up on Facebook if he's still around.

 

@douglasthecook I believe had a kit in his 4th gen. He hasn't been on here in 10 months but may have some info.

 

BTW, someone in AZ over on advrider.com has a big bore 5th gen for sale.

  • Member Contributer
Posted

My RC36 is an 837cc, and although the pistons were purchased in the UK in the early 2000s, I believe they were sourced via Dynamo Humm (because Brian owned the piston spec used by JE to make them).  Unfortunately, I don't know which jets are in the carbs.  However, if you're going to get the engine tuned on a dyno (which would be wise, considering the set-up), the tuner should have a gazillion Keihan jets in stock to choose from.  

 

I might also have some info on an old Factory Pro Racing jet kit I have/had.  But I'd have to dig around for it.  ISTR I might have a photo of the instruction sheet (incl. jet sizes, albeit maybe those were Dynojet jets)?

 

[Found the Factory Pro data sheet.  It is for the early RC36, which may not be useful to you.]

 

Ciao,

 

JZH

 

VFR750F Factory Jet Kit Setup Sheet (1997).PDF VFR750F Factory Jet Kit Tuning Guidelines (1996).PDF

  • Like 2
Posted

JZH

 

The Data sheet  on Factory Pro, would be much appreciated.  They don't list whats in the kit, that I could find.

    josh.hunt@yahoo.com

On 9/19/2024 at 1:58 PM, vfrcapn said:

 

 

  • Member Contributer
Posted


No reply from my old contact, but it was a 14year old email address. 

  • 3 weeks later...
  • 1 month later...
Posted

JZH

You say you have one of these 840 “kits” in your bike.  I was wondering if you had to sleeve the block?
I have been under the impression that sleeves were not used/needed, but in reading back threads on this, one thread mentioned sleeves with the kit.

If sleeves are needed it would be a show stopper.

Any thoughts ? ? ?

Thanks

Josh

 

  • Member Contributer
Posted

The Dynamo Hum 840 used Iron liners. 
The biggest issue with 5/6th big bore is the MMC liner fitted by the factory. HighSideNZ used my research to make an 825cc using CBR929 74mm pistons, by boring out the MMC to 74mm. Any larger & you run out of MMC & because the exterior is castlelated you need to go out to a minimum 77mm, but probably 78mm to completely remove the MMC. That leaves a 5mm wall thickness on the open deck cylinder, so if you bored to 78mm & added a 1.5mm wall thickness liner you could run CBR954 pistons (same weight at 800's) for an 848cc engine. But its a lot of work & most places would not be able to bore the integrated top crankcase/block.
 

I had a thought the other day about using a alloy top hat liner that would add strength & be easy to water seal, but requires a very good machine shop to make & mill block to take it. 

Posted

Mohawk,

Do you know if this holds true for the 4th Gen. 750s?

  • Member Contributer
Posted

All VFR 750's use Iron liners AFAIK. You can use Nikasil compatible piston rings on an Iron bore but NOT the other way round. Nikasil/MMC is much harder than Iron. 
 

I've never researched big bores for the 750's but I believe they also have integrated block/crankcase. So boring them is an issue for many places. 

  • Member Contributer
Posted

I found a few references in my saved emails about the Dynamo Humm 840 kit and the Wolf exhaust. Not much technical help, but it might add a little colour to the current discussion.

 

VFRD - big bore VFR1, Brian Law.jpg

VFRD - big bore VFR2, Wolf exhaust.jpg

VFRD - big bore VFR3, JohnS.jpg

  • Thanks 1
Posted

Thanks Lorne. 

 

Any info. is great ! !  It sheds some more light on things.

  • 2 weeks later...
  • Member Contributer
Posted
On 11/26/2024 at 11:40 PM, Mohawk said:

The Dynamo Hum 840 used Iron liners. 
The biggest issue with 5/6th big bore is the MMC liner fitted by the factory. HighSideNZ used my research to make an 825cc using CBR929 74mm pistons, by boring out the MMC to 74mm. Any larger & you run out of MMC & because the exterior is castlelated you need to go out to a minimum 77mm, but probably 78mm to completely remove the MMC. That leaves a 5mm wall thickness on the open deck cylinder, so if you bored to 78mm & added a 1.5mm wall thickness liner you could run CBR954 pistons (same weight at 800's) for an 848cc engine. But its a lot of work & most places would not be able to bore the integrated top crankcase/block.
 

I had a thought the other day about using a alloy top hat liner that would add strength & be easy to water seal, but requires a very good machine shop to make & mill block to take it. 

 

Not on my engine!  840 = no sleeves.  The "kit" consisted of pistons, rings and pins--and nothing else.  IIRC, there was also a TTS 840 kit for the 5th gen, which did not require sleeves.  (That may be the one I bought several years ago which is still in my garage somewhere.)

 

Ciao,

 

JZH

  • Member Contributer
Posted

To bore out the MMC you need at least a 77mm bore possibly 77.5 or 78mm to clear it. That makes an 893cc @77mm or 916cc @78mm. Also reduces the 8mm open deck wall to 5.5 or 5mm, reducing the sealing area & clamping force on the head gasket. 840cc is approx 74.5mm bore which may be possible within the MMC but leaves precious little MMC approx 0.75mm wall assuming the MMC was cast central to the bore. Could end in disaster, hence I assumed they must be iron lined. 
 

I did have an idea to get alloy liners made with a 75mm bore & have them nikasil plated, then bore out the MMC to press fit the new liner & use CBR954 pistons, which have the same pin diameter & weight the same as stock VFR pistons so no stress load issues ! For a nice 848cc big bore. 
 

Time & Money needed to get that done. 

  • Member Contributer
Posted

To bring this back to the original post, the OP has a 4th gen engine and an 837cc big bore kit, but was wondering if the installation of those pistons would require sleeving the block/case.  In that case, no, installation would not require sleeves.  As evidence I offer: My RC36's 837cc engine was bored, not sleeved, and if sleeves had been required they would have been included in the kit.  (I'm pretty sure they were included in the Dynamo Humm 5th gen 870cc kit.)

 

Please note that, according to Brian Law ~25 years ago, boring the RC36 engine case properly can be very tricky.  Choose your engine-builder/shop carefully.  Bryan seemed to rate TTS in the UK (where my big bore kits were installed), but I recall him saying that VFR engine cases had been ruined by other shops which didn't know what they were doing.

 

(Also, don't expect a huge increase in power!  I did mine because I could.  It is very hard to justify the expense of this kind of mod.  A VFR750F will never be a CBR1000RR.)

 

Ciao,

 

JZH

  • 1 month later...
Posted

Just wanted to thank you all for the technical help.

 

The 840 was started up yesterday and sounds and feels just dandy.

 

Too bad it's Winter, It'll be awhile before I can ride it = located just off Cape Cod, Mass.

  • Like 4
  • Member Contributer
Posted

@douglasthecook  how is your big bore engine going??

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