Gen3 motor into a Gen1/2 bike - Triumph675.Net Forums
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post #1 of 35 Old 09-22-20, 16:58 Thread Starter
samwise_i
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Gen3 motor into a Gen1/2 bike

This conversation started over in thread:

https://www.triumph675.net/forum/sho...d.php?t=250909

I thought that I would start a new thread discussing this issue and what I have learned.

First, why would anyone want to do this? Well, for me, I want(ed) to put a street triple 765 motor in a Gen1 Daytona that I already have. IMHO the 765 ST motor is a more usable for the type of riding that I enjoy, twisty roads. Since I don’t track the bike much due to the expense, a high revving engine is not a huge plus. I am much more interested in good mid-range power which was one the reasons I bought a triple in the first place.

So, you might ask why not just buy a ST 765 and that would be a good question. I took one for a test drive at my local dealer and instantly fell in love with the motor, but the looks of the bike are not to my liking. I still think that the Gen1/2 Daytonas are beautiful bikes; not sure what Triumph was thinking with the Gen3 bikes:-)

A couple of months ago I came across a ST 765 motor locally and pulled the trigger after convincing myself that it would physically fit in the frame which it does. I then started looking at what else would be required to make it work.

ECU:
One of the first things that I investigated was whether I could make my Gen1 ECU work with the newer motor. I did a bunch of research and could not find anyone that had done this. I then remembered talking to JDGun a long time ago about a similar swap and reached out to him. He graciously agreed to a phone chat and downloaded a bunch of info that I was not aware of. One of the things that he told me was the CPS(Crankshaft Position Sensor) on the Gen3 motors is at a different different angle with respect to TDC. Since the ECU bases ignition timing on this angle, a different location would/could be a problem using a Gen1/2 ECU.

Throttle Bodies:
The newer ST motors use ride by wire throttle which requires the new ECU and wiring harness. This can be worked around if you fit the Gen1/2 throttle bodies to the Gen3 head which appears to work.

Airbox:
The Gen3 air box is completely different and will not fit in the Gen1/2 without modification. I was able to fit my Gen1 airbox and it appears to fit. Since the engine tuning is effected by the airbox geometry it would need to accounted for with a new tune.

Exhaust:
The exhaust for the 765 is unique to the ST and will not easily fit a Gen1/2 bike. The header runs on the opposite side underneath the motor and would require a custom mid-pipe to hook everything together. Not impossible, but not plug-play.

Breather:
And then there is the breather which is a totally different shape on the Gen3 than on the Gen1/2. I did not even think about this, but JDGun informed me that for it to fit under the gas tank it would need to be modified.

Coolant Hoses:
Some of the ins and outs are different, but these can be easily worked around.

So in summary probably the biggest problem is the ECU. The simple way to solve it would be to use a Gen3 ECU, wiring harness, and panel, but this could get expensive.

Last edited by samwise_i; 10-03-20 at 15:07.
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post #2 of 35 Old 09-22-20, 16:59 Thread Starter
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post #3 of 35 Old 09-22-20, 17:01 Thread Starter
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post #4 of 35 Old 09-22-20, 17:48
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Excellent info, thanks for sharing the wisdom. This type of info is what forums are all about.

Judging by what you’ve said I think the easiest way to get a gen3 engine into a gen1/2 is to reuse all the gen1/2 parts (throttles, airbox, throttle cable etc).

Attempt Modify the breather to work with a gen1/2 tank.
Attempt to fit a gen 2 stator/trigger wheel onto the gen3 crankshaft.

The ST765 may pose another issue regarding the header, but wouldn’t a 675 gen3 header resolve this?


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post #5 of 35 Old 09-22-20, 19:48 Thread Starter
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Quote:
Originally Posted by nlzmo400r View Post
Attempt to fit a gen 2 stator/trigger wheel onto the gen3 crankshaft.
I don't see an easy way to do this; maybe I am missing something. If you come up with something please share with the rest of us.

Quote:
Originally Posted by nlzmo400r View Post
The ST765 may pose another issue regarding the header, but wouldn’t a 675 gen3 header resolve this?
The Gen3 Daytona header is still different at the exhaust end than the Gen1/2 header. This would still require a custom adapter to go from a Gen3 header to the Gen1/2 mid-pipe assuming that you would still use the undertail exhaust.
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post #6 of 35 Old 09-22-20, 19:59
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Quote:
Originally Posted by samwise_i View Post
I don't see an easy way to do this; maybe I am missing something. If you come up with something please share with the rest of us.



The Gen3 Daytona header is still different at the exhaust end than the Gen1/2 header. This would still require a custom adapter to go from a Gen3 header to the Gen1/2 mid-pipe assuming that you would still use the undertail exhaust.

I’ve not looked into swapping trigger rings, but it’s a potential solution perhaps if one could be retrofitted.

Regarding headers, ideally the gen1 header would be reused but with oval adapters instead of round to match the exhaust ports.


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post #7 of 35 Old 09-29-20, 13:22
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I was thinking about the same swap 765 into Gen2 bike.
My plan with the exhaust was to swap 765 sump for gen1/2 sump and just use the Gen2 exhaust system with oval headers and then some minor tweaks at the head if needed. I'm not 100% sure sumps are compatible...

Interesting re: crank angle sensor can you confirm that the pickup angle and or trigger wheel are different?

If it's just the pickup angle then a 'known' constant can just be added to the whole map in tuneecu or tuneboy. Not the prettiest solution though...

How does the front sprocket alignment go with the swingarm pivot point?
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post #8 of 35 Old 10-01-20, 16:52 Thread Starter
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Quote:
Originally Posted by ditto675 View Post
...My plan with the exhaust was to swap 765 sump for gen1/2 sump and just use the Gen2 exhaust system with oval headers and then some minor tweaks at the head if needed. I'm not 100% sure sumps are compatible...
The Gen1/2 and Gen3 sumps are not compatible.


Quote:
Originally Posted by ditto675 View Post
Interesting re: crank angle sensor can you confirm that the pickup angle and or trigger wheel are different?
I have only visually inspected it and it does look different. JDGun has actually tried it and told me that they are different.


Quote:
Originally Posted by ditto675 View Post
If it's just the pickup angle then a 'known' constant can just be added to the whole map in tuneecu or tuneboy. Not the prettiest solution though...
My understanding is that there is not enough variability to allow for that, but I have not done this. I have yet to contact Alaine from TuneECU to confirm.

Quote:
Originally Posted by ditto675 View Post
How does the front sprocket alignment go with the swingarm pivot point?
Did not get there since I am putting my Gen2 engine back in after a refresh. The 765 is on hold until I can spend more time on it. Supposedly JDGun actually rode his bike with the Gen3 engine so I would assume that the alignment is correct, but I have not checked.

Last edited by samwise_i; 10-03-20 at 18:06. Reason: Fixed an error
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post #9 of 35 Old 10-01-20, 23:03
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Did some searching and found some positive stuff...

From Luca at Spirit Motorcycles

"You can fit a 675 full system to the bike in order to do this you wouldneed a 675 sump and oil pickup these are very easy to swap over once fitted a675 full system will fit a 765."

So a Gen3 sump #T1230118, Gasket #T1230114, pickup #T1210282 and breather tube #T1210283 with Gen3 exhaust headers matted to a Gen1/2 cat back will work on the 765 block.

Tuneecu allows values of -4 to +55 in the ignition table. 'Normal' values are from 0 to +48. So as long as the 765 pickup is physically located within 4 to 7 degrees positive or negative of the 675 pickup location most tuning conditions can be accommodated....

Last edited by ditto675; 10-05-20 at 14:43.
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post #10 of 35 Old 10-01-20, 23:38
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It also appears the alternator gasket is used by both Gen3 and 765 so another option might be to use a Gen3 alternator cover and pickup if the pickup location closer matches the Gen1/2 in terms of degrees btdc so that the std Gen1/2 ecu can be used.

The alternator rotor/trigger wheel is shared between the Gen3 and 765 so it is unlikely the the pickup is in a different location between them......still might be worth a look however.

Last edited by ditto675; 10-01-20 at 23:47.
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