Triumphrat

InkSlinger · 01-08-2009, 10:49 AM

I am thinking of going with the 904 kit this winter. I have heard that sometimes there are problems with cylinder base gaskets leaking oil. Have any of you with the Big Bore kits on your bike had this problem?

The kits seem to come with 10.5 and 11.5 compression ratios. Is 11.5 to high for pump gas?

What about valve sizes, do I need larger valves?

Thanks, Matt

mikeinva · 01-08-2009, 01:09 PM

Just like stock parts they dont leak unless something is wrong.bigger valves will give more hp .You need to have the head ported by someone who knows what he is doing .I have 2mm over intake and exh valves in mine but im not sure 1mm over wouldnt run just as good.I have 10.5 in mine some go with the 11.5 with out trouble.I guess it depends on how good of gas you can get every where you ride .I run 92 or 93 octane in mine with no troubles.To get the motor to run good you will need ether 39mm or 42mm carbs and some good pipes.If you have a 865 motor you might think of getting some better cams to like tpusa 813.The 865 cams are dead after 6500 rpm compared to older 790 cams.Then you might want to get with pieman and get your ing box remaped with more advance and up rev limit to 8500 rpm .
From all the dyno sheets i have seen I cant see much hp gain with the 11.5 to 1 kit over the 10.5 kit .BP runs 13.5 on there race bikes with race fuel and they are like 5 hp faster then there 10.5 kits so who knows .Both the 10.5 and 11.0 kits can make over 80 rear wheel hp if everything is right.

MONTTU · 01-08-2009, 04:31 PM

Do not use base gasket, glue the cylinder block to engine case with high quality sealant like Honda bond. That is commonly used with japanese racebikes. Just check that there is enough clearance beetween piston and head without base gasket (at least 0,8 mm, 0,9 mm is clearly on safe side).
It will not leak and gives more compression and squench effect.

InkSlinger · 01-08-2009, 05:46 PM

Thanks, I talked to BP and they recommended 1mm Int. and Exh.oversize valves with the addition of an inner valve spring. I will get the heads flowed at a local shop with alot of racing experience. Wow, Mikuni carbs are frickin expensive!!! I will have to wait until tax time to get the carb kit. Until then I will have to "limp" along with the stock carbs. Cams will probably be the next thing . Anybody got a recommendation for jetting with a 904 and stock carbs at sea level? In the meantime I will check out the search function. Thanks

vertwrks · 01-08-2009, 06:07 PM

I have not had any base gasket issues at all. Went with 1mm over and no inner spring. The guy that did the port and sleeve pressing was certain the stock spring was good for 1mm over. You can go 1mm over easily with the stock valve seats. Not sure if those who went 2mm required new seats, if so that would up the cost some. Pulls strong all the way to the Procoms redline so I don't expect I am getting any valve float.

mikeinva · 01-08-2009, 07:02 PM

Quote:

Originally Posted by MONTTU

Do not use base gasket, glue the cylinder block to engine case with high quality sealant like Honda bond. That is commonly used with japanese racebikes. Just check that there is enough clearance beetween piston and head without base gasket (at least 0,8 mm, 0,9 mm is clearly on safe side).
It will not leak and gives more compression and squench effect.

That is not right you shouldnt be telling people to do that .you have to use the gasket on these motors to get the deck height right its a metal gasket .The 904 kits are set up for these gaskets

mikeinva · 01-08-2009, 07:06 PM

Quote:

Originally Posted by vertwrks

I have not had any base gasket issues at all. Went with 1mm over and no inner spring. The guy that did the port and sleeve pressing was certain the stock spring was good for 1mm over. You can go 1mm over easily with the stock valve seats. Not sure if those who went 2mm required new seats, if so that would up the cost some. Pulls strong all the way to the Procoms redline so I don't expect I am getting any valve float.

the single spring will work for awhile but if you do much high rpm running the dual spring will hold up better.

InkSlinger · 01-09-2009, 08:57 AM

vertwerks, have put your bike on the dyno? I'm really interested to know what kind of power you are making since I'm basically doing the same thing. Is your cam stock? I'm looking at the TP 813's.

MrTwin · 01-09-2009, 01:42 PM

No issues with my engine. Upon assembly I made sure all mating surfaces and stud treads were clean and spotless. Torque per specs.

MONTTU · 01-09-2009, 03:52 PM

Quote:
Originally Posted by MONTTU
Do not use base gasket, glue the cylinder block to engine case with high quality sealant like Honda bond. That is commonly used with japanese racebikes. Just check that there is enough clearance beetween piston and head without base gasket (at least 0,8 mm, 0,9 mm is clearly on safe side).
It will not leak and gives more compression and squench effect.
T

Quote:

hat is not right you shouldnt be telling people to do that .you have to use the gasket on these motors to get the deck height right its a metal gasket .The 904 kits are set up for these gaskets

Mike,

What is the head to piston clearance you are using. I am running pistons over the deck.