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RETRO LATE MODEL '81-'83 CRANK INTO '78 CASE

scottholl

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From my research into the engineeering changes that were incorporated into the TSS & TSX model, there were changes to the crank by machining the crank journals differently to help reduce vibration by making the crank stiffer.
But, I am not yet aware of what changes were incorporated to accomodate the 4 valve head, push rods, push rod tubes, con rods, pistons and piston pins.

My idea was trying to querry this community and see if I could learn if a MODEL '81 THRU '83 CRANK could be accepted INTO A '78 CASE. A rather Bat :shit: crazy idea by trying to build a faux TSS / TSX or at least try to gain some of the TSS / TSX improvements into my 78 bonnie. I hope my mechanical fantsies will generate a great discussion. I also offer my thanks in advance to whomever may bwe able to contribute to this post.

Additionally, I continue my investigations into the 2 UK vendors that offer a retrofittable electric start kit for unit construction twins (i have posted heavily on this subject) My intentions are to use my Covid stimulus funds to actually purchase one of these kits and see how far I can go to get it installed on my '78 bonnie 750. I am still trying to find someone that can provide some kind of installation instructions for this modification as each vendor's kit approaches the modification of the intermediate gear's spindle differently. Until I can obtain technical responses from these 2 UK vendors, I am left with an assumption that 1 kit can be applied by just working inside the timing case cover without splitting the case halves. Whereas, the other vendor kit appears to probably have to do work both inside the timing cover and probably need the cases split because this kit requires a removal of the intermediate gear spindle bushing in order to introduce a stronger spindle bushing that once pressed in (?) has to be reamed to size in order to incorporate a new intermediate gear spindle and its associated sprag and new timing gear cover and starter. Quite a kettle of fish. regards Scottoe
 

Rudie

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From my research into the engineeering changes that were incorporated into the TSS & TSX model, there were changes to the crank by machining the crank journals differently to help reduce vibration by making the crank stiffer.
Last available parts books ('82) have the same crank and rods part numbers (71-3298, 71-3006 respectively) as '78 in everything except the TSS.

TSS crank has larger-diameter big-ends and corresponding rods. The main bearings are the same as the other '82 models so it might be theoretically possible to fit a TSS crank in another OIF; however, as Meriden made only just over four hundred TSS total, probably not that many good used cranks lying around.

I have it mind (but I am not sure) TSS bore centres are further apart than 2-valve twins? If so, rods small ends would be desaxe, would not fit 2-valve pistons or block.
 

scottholl

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Last available parts books ('82) have the same crank and rods part numbers (71-3298, 71-3006 respectively) as '78 in everything except the TSS.

TSS crank has larger-diameter big-ends and corresponding rods. The main bearings are the same as the other '82 models so it might be theoretically possible to fit a TSS crank in another OIF; however, as Meriden made only just over four hundred TSS total, probably not that many good used cranks lying around.

I have it mind (but I am not sure) TSS bore centres are further apart than 2-valve twins? If so, rods small ends would be desaxe, would not fit 2-valve pistons or block.
Rudy, thanks for you valued explanations. I hope this topic generates more cross communications through-out this community. I am going to ask the 2 UK vendors that promote their electric start assembly, to investigate if they can find any NOS TSS blocks, push rods and P.R.cranks or 4 valve heads. When I learn more I will advance any further knowledge that I might learn, regards Scottoe
 
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tobyb

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The cranks are interchangeable, the main difference is the min bearings where up graded, balance factor change and the comp was reduced to 7.5/1. As well as parallel intake ports and MK2 Amals. Be careful with the TSS heads and barrels, the first series where porous and cost the company heaps in warranty repairs.
 

TSS_rider

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TSS compression was increased due to redesigned, more efficient combustion chamber. Offset connecting rods gave more distance between cylinder bores. Rocker geometry changed as well. I would be very skeptical about interchangeability with 78 bonny. I don't think the tss rods would be centered. Tobyb, can you elaborate please.
Regards
 

tobyb

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My answer was to his question re
81-83 cranks not the TSS.
 

scottholl

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guys thanks for forwarding this theoretical day dreaming. was were the 81 thru 83 cranks - did they gain any engineering change that resulted in a better i.e., stiffer crank ? or was it only the TSS & TSX(?) cranks that had the desirered benifits? Have I mis attributed the improved crank characteristics to the 81 thru 83 cranks? Would there be any benifits for improvement by seeking to transplant an 81 - 83 crank into my 78? It amazes me that there are people that have acquired this type of engineering history. thanks scottoe
 

grandpaul

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There happens to be a complete, overhauled, 8-valve engine for sale (forget where I saw the link). It was already over 2500 GBP, so likely to be higher...
 

scottholl

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There happens to be a complete, overhauled, 8-valve engine for sale (forget where I saw the link). It was already over 2500 GBP, so likely to be higher...
grandpaul

thanks i did a cursorary search but couldn't dig up any leads also learned that some of the TSS added an "AV" modification derrived from bikes going to british police - "AV" anti vibration engineering change

thanks scottoe
 

tobyb

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grandpaul

thanks i did a cursorary search but couldn't dig up any leads also learned that some of the TSS added an "AV" modification derrived from bikes going to british police - "AV" anti vibration engineering change

thanks scottoe
The AV engine mounts will fit 8881 on Bonnies and came std on the last of the Executive models as well. A couple of yrs ago a guy had a set for sale on Ebay, trouble was he listed them separately. I now have one of them and 2 other people have the other 2.
 

scottholl

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Will any parts fische so these mounts - how about a picture if possible

thanks
 

scottholl

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The AV engine mounts will fit 8881 on Bonnies and came std on the last of the Executive models as well. A couple of yrs ago a guy had a set for sale on Ebay, trouble was he listed them separately. I now have one of them and 2 other people have the other 2.
Toby,
Did you make a typo ? don't understand your description will fit 8881 - regards

scottoe
 

grandpaul

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I believe he meant to type "1981"
 

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Will any parts fische so these mounts - how about a picture if possible
They are in the 81 and on parts manuals.
There is only one '81 parts manual online - https://partsbooks.britishonly.com/partsbooks/20-10116C.pdf - it doesn't show any difference in the engine mountings from '80 or '82 except the TSS.

@scottholl is not very experienced, he will not know what AV parts look like; some more detail - parts manual page numbers, part numbers? - might help him more?
 

scottholl

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