94 Speed Triple, High compression pistons.... - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 9 (permalink) Old 07-19-2019, 04:22 PM Thread Starter
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94 Speed Triple, High compression pistons....

Hey there, wondering if anyone could help me on this one. I am looking for information on swapping my original pistons in my 94 Speed Triple with the pistons from a 750. I hear they increase compression/performance. Has anyone done this? I am about to start rebuilding my engine and would fit the 750 pistons if the upgrade was a winner.

Will it run? Is it worth it? Do i need to run higher octane fuel? Will a standard head gasket be sufficient? Do I need to change the cams or con-rods?

Any info would be greatly appreciated!

Andy
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post #2 of 9 (permalink) Old 07-21-2019, 01:39 PM
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I've done it, and have been pleased with the results.

It's a straight piston swap. You can re-use your existing rings etc, if you want to, but best practice is to change the rings, gudgeon pins, and circlips whilst doing it I suggest. Taking the head off will require a new head gasket in any case.

Assuming you are not modifying carbs or exhaust at the same time (there is no need), you don't need to change fuel or carb settings on your bike or change your cams (though I always re-balance the carbs after a strip-down).

If you are on the standard green cams, the increase of compression (from about 10:1 to somewhere around 12:1) equates to between an extra 5-10bhp, which seems to be most noticeable when you get the revs above 5-6K.

Add a couple of teeth to your rear sprocket, and your bike will feel quite a bit more lively! 😁
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post #3 of 9 (permalink) Old 07-21-2019, 01:41 PM
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Check out www.mottleybiker.com for some useful tips on carrying out the work without removing the engine.
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post #4 of 9 (permalink) Old 07-21-2019, 01:55 PM
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Oh, and you might want to go up one cooler on the spark plugs - use an NGK DPREA9-9 instead of the DPREA8-9 that you might be currently using
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post #5 of 9 (permalink) Old 07-22-2019, 01:58 PM Thread Starter
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Niiice one Stuart, thanks for sharing, much appreciated

I have the engine stripped completely and am rebuilding her with a new set of bearings,rings and cam chain etc. I was gifted the bike last year, as the fella who had it before me didn't see himself having the time to rebuild her. It seems it was a project that had gone through a few hands before me and was never finished.

When I got the bike the engine was already out sitting on a pallet. Practically all the bits of the bike were in boxes. A new tank, wheels, shocks and custom handle bars where the only bits attached to the frame. There was two custom aluminum mud guards in a box that someone obviously put a considerable amount of time into making. It also had the seat frame chopped halfway and raised up at the back with two Harley Davidson straight through cans that fit neatly under the seat. This yoke looks like its straight out of a Mad Max movie.

The project had been abandoned and had been lying up for a few years. Unfortunately the engine was seized solid and when I started investigating I found that one of the cam chain guides had snapped and was jammed in the crank sprocket! (glad i wasn't on the bike when that happened!!)...

I decided a complete strip down and rebuild of the engine was the safest option to check everything and make sure there was no further damage. So far so good! I've never ridden a speed triple before and was told they could do with a few more horses and that changing to 750 pistons was a good option.

Its nice to hear from someone who has actually done it, so thanks again for the info

Andy
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post #6 of 9 (permalink) Old 07-29-2019, 12:20 PM
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Hi Andy, The 750's weren't imported into the United States so I don't know much about the 750's. However I do know that Triumph wisely used many of the same parts on many of their bikes. I suspect the 900 Daytona's used the same pistons as the 750's. My brother Super III had high compression pistons with red cams. We loved that bike. I've read that the 750 had a shorter stroke than the 900's and was able to have a higher redline, something like 10.5K or 11K. To achieve this higher redline it had a different CDI box than the 900's. Good luck with the build. It's great fun, I've built 3 bikes from dead Ebay parts.
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post #7 of 9 (permalink) Old 07-31-2019, 09:03 AM Thread Starter
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Hey Greg thanks for your response. I'm looking for 750 pistons at the moment but having difficulty getting no.2 piston. Do you know what the difference is between pistons 1&3 (1120005-T03) and piston 2 (1120007-T0301)? I cant find any differences between the pistons i have already. They look and measure the same, however piston 2 has +2 marked on the inside beside the Triumph logo. Do you know if i can I use a piston 1/3 to replace piston 2? Are you able to shine any light on this for me?

Andy
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post #8 of 9 (permalink) Old 07-31-2019, 10:55 AM
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Hi Andy, I also weighed and measured the pistons, I could find any difference between 1,2, and 3. I've rebuilt about 5 engines and they all run great. I'm in the process of moving to Arizona, when I get unpacked I'll have a look to see the +2 in my collection of pistons.
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post #9 of 9 (permalink) Old 07-31-2019, 03:22 PM Thread Starter
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Thanks Greg, weighed?.....niiice did not think of that! After having had another look it says +3 on the piston not +2 as i previously stated. Happy packing/unpacking Thanks for the help.
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