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Can the 904 kit be reversed and the original displacement be restored? Whats involved?
Yes, but only by buying new/used standard barrels (cylinders), pistons and rings. When a 904 kit is fitted the original liners are removed and the barrels are bored out to accept the larger liners that the 904 kit requires this means that standard liners, assuming that you can obtain them, will no longer fit those barrels.
 

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I believe that our Barrells don't use liners. They are Nikasil plated.

One of the 904 kits does use liners though, that is true.

So as everyone said, you need new barrells, and pistons and rings if you don't have the old ones.

Are you removing one, or are you considering doing the mod but want to know about reversability?
 

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Yes that is true - new barrells would be a necessity.

Or custom liners I suppose, but I doubt that would be cost effective.
 

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Discussion Starter · #8 ·
I need to get in on this :D ok how bout 26% and my stock parts ? :cool: LOL
haha Nice try...um no.

Anyway, the bike I bought was quoted to have the 904 kit in it. After investigating, the guy that had the bike said he sold the kit. (no more info yet).
I have done a basic compression test, (in gear and tried to roll the bike) and the wheel locks up and will roll past TDC with effort. I have also spun the stator so i dont mean engine lockup.

Seems odd that someone would put the kit in, then sell it, then even bother to put the old ones back in.
How do you think i might tell if the pistons are flapping around in the barrels ?
I don't mind buying the 904 kit, but it would be nice to get as much info as I can 1st.
BTW I have very little communication with the original owner.
 

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He must not have installed the 904 kit at all.

If he had put standard pistons back in the 904 barrells it would sound horrendous when you turned it over, and wouldn't even start. You certainly wouldn't get any compression.
 

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the 904 is 6mm bigger bore if it was a 790 it wouldnt run at all if he put stock pistons in the 904 bores.The only way to know what you have is to pull the head.
 

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Discussion Starter · #11 ·
He must not have installed the 904 kit at all.

If he had put standard pistons back in the 904 barrells it would sound horrendous when you turned it over, and wouldn't even start. You certainly wouldn't get any compression.
I havent started it at all...ever. I have had it for 2 weeks. I havent started it because I need a clutch cover which is on its way.

I will be checking and resetting timing before it even gets a thumb on the start button.


the 904 is 6mm bigger bore if it was a 790 it wouldnt run at all if he put stock pistons in the 904 bores.The only way to know what you have is to pull the head.
Its an 06 thruxton so the original is 865 right? I really dont want to remove the head if I dont have too. would the original 865 pistons in a 904 bore give any compression?
"Now where did I put that compression tester..."
 

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I just spoke to the previous owner, and he said that he removed the 904 liner and put the original 865 back in. apparently there is no difference in the outside diameter, and therefore the original liners have been placed back in with the original pistons and all torqued up.. Again he explained there is nothing more to do here than the timing as the cams have been removed and the originals put back in as well...
 

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Discussion Starter · #13 ·
ok, so for some more clarification. The previous owner (good guy) has told me what he did. He bought the outer casing (barrells) with the 904 installed. The bike has had the original barrels installed back in it with the original pistons and bolted back together. It has been run with the original parts back in so the proof is there that its all good. PHEW!:D
 

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Oh the original jugs were put back on the bike with the original pistons, so that explains it.

There have been no regretful cases of 904 kit installs that I'm aware of. Not the TPUSA ones anyway, which involve boring the jugs out and replating them with Nikasil. That's the way to go, and I am hoping to do that myself this year (probably a winter project). Should be fun.
 

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Getting back OT a bit...Mike, which path do you think is better?...boring through the nikasil plating and replating?...or sleeving bored Nikasil jugs? Boring/replating maybe more expensive then boring and resleeving with iron. Weight and heat transfer are an issue with iron sleeves compared to Nikasil plating. Structural strength of boring and replating without the strength of iron sleeves as mentioned "may" be a factor...unconfirmed...due to distortion over time due to heat cyling.
How does the economics comparing the two approaches shake out?
Thanks,
Geroge
 

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You should check out the TPUSA website George, they have some great performance products:

www.triumphperformanceusa.com

I can tell you this much - TPUSA actually test and run all their performance stuff in our bikes, so they know their stuff works. Not all the aftermarket manufacturers do this, so if you want a big bore kit this is your safest option. Like I say I have evry intention of doing just that.
 

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Thanks Prop.
To me...a bit of a jump ball.
BB Nikasil replate kit: 39 cc's +.5 pt. more compression
versus:
no change in bore + 11:1 CR (still good) + 813-S cams...for less money.

Replating the bores if not worn which apparently is pricey may not be worth it for 39cc's and a half point of compression is my thought without the cams in the mix.

Prop...the latter package maybe calling my name this winter. I won't have that many miles on my bores come winter with all that I have going on so...HC pistons + 813 cams maybe the best bang for buck for me.

Thanks,
George
 

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Yes it all depends what kind of thing you want - the new high compression ratio kit is a very nice kit for the money. The 904 takes you down the hot rod path - very much fun if that's your thing. I had been considering a stroker motor - but I think the 904 kit, FCR39s and some headwork will do me very nicely - I think that will make quite a nice monster bike. I'm looking forward to that.

George, I hope you do the stock bore higher compression kit and post your findings, I know you won't be disappointed.
 

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The thing Prop that gives me pause to consider putting HC pistons into my stock bores is...all reports including ledinger's suggests that the Nikasil plated cylinders are bulletproof and wear very little even with moderate mileage. Resleeving has its tradeoffs and replating for only 39 more cc's may not be considered a good value for benefit derived. If TPUSA sweats the details as you say with their R&D and did their homework for sizing their forged HC pistons to the stock bores...those coupled with the killer 813-S cams seems like the best ticket. Compression and cams are what these stock motors need IMHO.
Winters are long and I always need a project.:cool:
George
 

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You can run a tighter piston to wall clearance in nikasil than you can in iron sleeves. Just another plus.

I was really skeptical about this nikasil stuff....but I am starting to like it.
 
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