scup33 Posted September 18, 2024 Posted September 18, 2024 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 Quote
Member Contributer vfrcapn Posted September 19, 2024 Member Contributer Posted September 19, 2024 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? 1 Quote
scup33 Posted September 19, 2024 Author Posted September 19, 2024 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. 1 Quote
Member Contributer Mohawk Posted September 19, 2024 Member Contributer Posted September 19, 2024 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. Quote
scup33 Posted September 19, 2024 Author Posted September 19, 2024 That would be mind boggling ! ! ! THANKS Quote
Member Contributer vfrcapn Posted September 19, 2024 Member Contributer Posted September 19, 2024 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. Quote
Member Contributer JZH Posted September 22, 2024 Member Contributer Posted September 22, 2024 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 2 Quote
scup33 Posted September 24, 2024 Author Posted September 24, 2024 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: Quote
Member Contributer Mohawk Posted September 24, 2024 Member Contributer Posted September 24, 2024 No reply from my old contact, but it was a 14year old email address. Quote
scup33 Posted November 26, 2024 Author Posted November 26, 2024 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 Quote
Member Contributer Mohawk Posted November 26, 2024 Member Contributer Posted November 26, 2024 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. Quote
scup33 Posted November 26, 2024 Author Posted November 26, 2024 Mohawk, Do you know if this holds true for the 4th Gen. 750s? Quote
Member Contributer Mohawk Posted November 26, 2024 Member Contributer Posted November 26, 2024 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. Quote
Member Contributer Lorne Posted November 27, 2024 Member Contributer Posted November 27, 2024 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. 1 Quote
scup33 Posted November 28, 2024 Author Posted November 28, 2024 Thanks Lorne. Any info. is great ! ! It sheds some more light on things. Quote
Member Contributer JZH Posted December 10, 2024 Member Contributer Posted December 10, 2024 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 Quote
Member Contributer Mohawk Posted December 10, 2024 Member Contributer Posted December 10, 2024 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. Quote
Member Contributer JZH Posted December 11, 2024 Member Contributer Posted December 11, 2024 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 Quote
scup33 Posted January 13 Author Posted January 13 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. 4 Quote
Member Contributer Dutchy Posted January 13 Member Contributer Posted January 13 @douglasthecook how is your big bore engine going?? Quote
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