Hi, does anybody know where I could find an over sized valve kit for my xr70 head? I would like to buy valves and seats as a kit if possible. I am a machinist and a motor head, and I would like to see what I can do with this 70 head. Thanks for any leads
Looking for a 25/22 valve kit for xr 70 head
nickp
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Hi, does anybody know where I could find an over sized valve kit for my xr70 head? I would like to buy valves and seats as a kit if possible. I am a machinist and a motor head, and I would like to see what I can do with this 70 head. Thanks for any leads
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10,917 Posts
Here is a Valve kit
its for the TB Race heads
[h=1]TB Valve Kit for Race Head ( Honda )
Part No: TBW0380
Location: 218I[/h]
Race head valve kit (Honda)
Includes:
Intake:
25 mm Valve diameter
66 mm Length
Stem Dia 5.0 mm
Exhaust:
22 mm Valve diameter
66 mm Length
Stem Dia 5.0 mm
Springs
Keepers
Rockers & Pins & Adjusters
Retainers
Seals
its for the TB Race heads
[h=1]TB Valve Kit for Race Head ( Honda )
Part No: TBW0380
Location: 218I[/h]
Race head valve kit (Honda)
Includes:
Intake:
25 mm Valve diameter
66 mm Length
Stem Dia 5.0 mm
Exhaust:
22 mm Valve diameter
66 mm Length
Stem Dia 5.0 mm
Springs
Keepers
Rockers & Pins & Adjusters
Retainers
Seals
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11,849 Posts
There shouldn't be any need for bigger seats, I believe the 25/22 valve stems are the same diameter as the stock 70 valves are. I rebuilt an XR70 head using the older 23/20 Race Head rebuild kit that TB used to sell, with no issues at all.
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113 Posts
Okay then I have another question for you. Is there any advantage to running oversized valves for my aplication then? It seems to me the idea of running larger valves is because you added larger seats with a bigger I.d.. Larger valves without larger seats seems like I would just be adding a heavier valve without any performance gain...which would actually hurt performance. Or can I open the stock seat inside diameter up enough to make the bigger valves worth while? Thanks for your guys responses!
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I am guessing you don't machine motors. You have to machine the seats to a bigger diameter when you put in oversized valves, in order to make them fit.... So in turn allows more airflow. With that said the valves TBolt sells are normally made out of better quality metal and allows them to make them lighter to help performance. Another question is this a bike stock 70? Might want a bore kit in order to make the valves worth all this work.
R.R.N.S. - Rail Ruts Not S!u+s
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113 Posts
Baker, I am a tool maker but I do have a fair amount of experience doing machine work on motors. How much can you open up the I.d. Of the factory valve seats before they start losing their press? I don't want them pulling up when everything heats up. Common sense tells me the more I take out of them the less interference fit they will have to hold them in place. That's why I was under the impression I had to put bigger seats in when going to a bigger valve. It will definitely be less work if I can just bore the existing seats, so I'm good with that. But How thin can I take them.
The head is for my xr50 with a 52mm bore. Thanks guys
The head is for my xr50 with a 52mm bore. Thanks guys
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I was not bashing on ya man! Sorry it came out that way. I am not a motor builder just a enthusiast. You would have to reach out to a few of the motor heads that are on this forum for the nitty gritty of how much the head needs machined to fit the valves. You might even be able to reach out to tbolt to see if he has the specs for what tolerances you need! Good luck with build! Sounds like you will have a nasty little xr50
R.R.N.S. - Rail Ruts Not S!u+s
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Let me try and elaborate on the subject and answer some questions that have been brought forth.
-will bigger valves give more power?....to answer that honestly it's yes and no. A engine has to live in harmony and all components have to compliment each other. With that said just by adding bigger valves you may "potentially" see an increase in power, it really depends on the engine as a whole. With the factory crf70 head valve angles are super steep. If your running a aggressive cam you will have to sink the snot out of valves for overlap clearance which thus in turn will create a bunch of combustion volume leading to less compression unless dome is increase and/or larger displacement either via bore or stroke of a combo of such. I could go on for a long time on when it would make power and when it wouldn't buy I will stop here until I get more information such as bore and stroke numbers, cam grind, carb size, exhaust etc...
-generally speaking with the with the factory honda heads you can oversize at least 1mm with the factory seats. Some applications you can go as big as +2mm. I unfortunately don't remember with the stock 70 head. Anything bigger than 2mm will definitely need larger seats.
-so how much can you oversize with out losing your interference fit?.... My rule of thumb is 1mm less than than seats outer diameter, if I'm feeling really froggy I'll go 1/2mm less than seat OD but I really try to avoid that. Reason being is you need room for your top cut of valve job. If you have a 25mm OD seat and you place a 25mm valve head on that seats your top seat cut will be on aluminum and not the seat itself. Which technically you could do this just isn't good practice.
-what should you make inner diameters of seats?... Here are some guidelines. On the intake side you wanna keep seat ID and port throat between 85~90% of valve head diameter. So if your using a 25mm intake valve your seat/throat ID should fall between 21.25mm-22.5mm. You NEVER EVER wanna take Seat ID to full valve head OD. You have to have seat material there to do valve job so the valve will actually seal shut. Again when I'm feeling really greedy ill sometimes go more than 90% but valve job becomes quite the PITA so I would strongly suggest staying 90% or less. On the exhaust side same thing 85-90% of valve head OD. Me personally I never take exhaust seat ID's passed 88% for a few reasons. Exhaust ports are inherently more efficient than a intake port so you wanna be careful not to over scavenge charge. In the case of a 25/22 setup I would suggest staying at 85%. As with seat ID's there's a ratio from intake valve head diameter to exhaust head diameter and in my opinion 22mm on the exhaust is too big for the size of the intake. Also the exhaust valves sees more heat and the heat is dissipated via seat. With that said 45 or 46 degree seat cut is generally a little wider than the intake side so therefore more material is needed to achieve a good multi angle valve job.
-cons of bigger valves.... As you have already mentioned with larger valves generally comes more weight unless fancy lightening work is done such as cupping, stem undercutting yata...yata.. Or exotic materials such as titanium. With this additional weight valves are more prone to floating so then comes the need of heavier sprung valve springs.
-will bigger valves give more power?....to answer that honestly it's yes and no. A engine has to live in harmony and all components have to compliment each other. With that said just by adding bigger valves you may "potentially" see an increase in power, it really depends on the engine as a whole. With the factory crf70 head valve angles are super steep. If your running a aggressive cam you will have to sink the snot out of valves for overlap clearance which thus in turn will create a bunch of combustion volume leading to less compression unless dome is increase and/or larger displacement either via bore or stroke of a combo of such. I could go on for a long time on when it would make power and when it wouldn't buy I will stop here until I get more information such as bore and stroke numbers, cam grind, carb size, exhaust etc...
-generally speaking with the with the factory honda heads you can oversize at least 1mm with the factory seats. Some applications you can go as big as +2mm. I unfortunately don't remember with the stock 70 head. Anything bigger than 2mm will definitely need larger seats.
-so how much can you oversize with out losing your interference fit?.... My rule of thumb is 1mm less than than seats outer diameter, if I'm feeling really froggy I'll go 1/2mm less than seat OD but I really try to avoid that. Reason being is you need room for your top cut of valve job. If you have a 25mm OD seat and you place a 25mm valve head on that seats your top seat cut will be on aluminum and not the seat itself. Which technically you could do this just isn't good practice.
-what should you make inner diameters of seats?... Here are some guidelines. On the intake side you wanna keep seat ID and port throat between 85~90% of valve head diameter. So if your using a 25mm intake valve your seat/throat ID should fall between 21.25mm-22.5mm. You NEVER EVER wanna take Seat ID to full valve head OD. You have to have seat material there to do valve job so the valve will actually seal shut. Again when I'm feeling really greedy ill sometimes go more than 90% but valve job becomes quite the PITA so I would strongly suggest staying 90% or less. On the exhaust side same thing 85-90% of valve head OD. Me personally I never take exhaust seat ID's passed 88% for a few reasons. Exhaust ports are inherently more efficient than a intake port so you wanna be careful not to over scavenge charge. In the case of a 25/22 setup I would suggest staying at 85%. As with seat ID's there's a ratio from intake valve head diameter to exhaust head diameter and in my opinion 22mm on the exhaust is too big for the size of the intake. Also the exhaust valves sees more heat and the heat is dissipated via seat. With that said 45 or 46 degree seat cut is generally a little wider than the intake side so therefore more material is needed to achieve a good multi angle valve job.
-cons of bigger valves.... As you have already mentioned with larger valves generally comes more weight unless fancy lightening work is done such as cupping, stem undercutting yata...yata.. Or exotic materials such as titanium. With this additional weight valves are more prone to floating so then comes the need of heavier sprung valve springs.
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As someone has already mentioned it's not simply buy bigger valves, remove old and put new bigger valves and call it a day. Seats Must be machined for larger valve head diameters, in order to take advantage of those larger valves seat ID's need to be machined larger to the percents discussed. I see this a lot guy sends me there head and says I put larger valves in it but it didn't do squat and the rest of the engine merited that larger valves would give nice performance gains. Upon getting head seat ID's are sized for the smaller valves which yes the bigger valve with small seat ID's will still yield some better flow characteristics but not as it would if seat ID and throats were opened. Ideally to take full advantage of it porting would be the route to go.
As a tool maker/machinist you have the background/knowledge of how to machine but doing cylinder head work requires specialized equipment. If you have a serdi or something like a serdi then you got her licked. If you don't it's going to take a shit load of your time making jig, cutters, valve stem pilot etc... To cut the seats. Then the next question becomes what is your knowledge of valve protrusion and installed heights? Its one thing to machine cut seats but there's more to it than just cutting a fancy multi angle valve job. Valve protrusion is a must know to maintain proper valve train geometry and install heights is also a must know to insure you have proper seating and nosing pressures as well as clearances from things such as coil bind and retainer~valve seal clearance.
As a tool maker/machinist you have the background/knowledge of how to machine but doing cylinder head work requires specialized equipment. If you have a serdi or something like a serdi then you got her licked. If you don't it's going to take a shit load of your time making jig, cutters, valve stem pilot etc... To cut the seats. Then the next question becomes what is your knowledge of valve protrusion and installed heights? Its one thing to machine cut seats but there's more to it than just cutting a fancy multi angle valve job. Valve protrusion is a must know to maintain proper valve train geometry and install heights is also a must know to insure you have proper seating and nosing pressures as well as clearances from things such as coil bind and retainer~valve seal clearance.
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Ooh and I forgot this lil nugget of info. Valve guide bores and stem OD's. While I'm pretty certain the crf70 and say the V1 valves have same stem Diameters, it is something to keep in mind when your attempting to do such work. Yes they are both classified as 5mm stems but in reality when mic-ed most are under 5mm. Our mini heads generally fall between 0194"~0.196"(4.927mm ~ 4.98mm). So you will wanna keep this in mind and make sure to mic stems and check clearances. Nothing would suck worse then if you did all that work assembled it and had tight clearances and seized a valve. which generally results in total chaos wrecking everything in the top end. Plus this is also good practice. Guides IMO are probably ones of the most over looked component in the head. They play a HUGE role in the overall scheme of things. If you have a worn guide it will be difficult to get a good concentric valve job. Sure you could use a split pilot but the valve stem will still dance around in guide and when valve is shut will contact seat differently every time which then leads to premature wear, leaky valves potentially sheering valve head off or snapping a stem. All in which results to piss poor performance.
Hmm I think I covered everything if I missed something feel free to ask or if you leaf through my threads there are plenty of big valve head threads to view
Hmm I think I covered everything if I missed something feel free to ask or if you leaf through my threads there are plenty of big valve head threads to view
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3,191 Posts
Here are 2 info threads that may help in your quest
http://planetminis.com/forums/roost...-area/186832-part-2-bv-ing-head-added-bonus-tapping-into-animas-power-pics.html
http://planetminis.com/forums/roost-area/185778-custom-valves-explained-pics-video.html
http://planetminis.com/forums/roost...-area/186832-part-2-bv-ing-head-added-bonus-tapping-into-animas-power-pics.html
http://planetminis.com/forums/roost-area/185778-custom-valves-explained-pics-video.html
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Yes sir gotta get a game plan before you can make chips. You wanna measure seats outer diameter to determine what valve head diameter can be used with stock seats not inner diameter. Being the seats are pressed in the head you won't be able to get a 100% accurate measurement. but with all carbon soot removed from combustion chamber you will be able to distinguish seat from aluminum. Then Take a set of calipers and get a rough outer diameter measurement of intake and exhaust seat. If intake seat is 26mm or bigger your good for 25mm intake valve and if exhaust is 23mm or bigger your good for 22mm valve. Then the real fun comes into play how much do you gotta sink those valves in order to have cam overlap clearance, achieve targeted valve protrusion, combustion chamber profiling/blending. It's been many years since I did a 70 head but if memory serves right, I'm about 90% certain you'll need larger seats for 25/22 valves. Putting 25/22 valves in a 70 head can be done....been there done that. even done a number 50 heads with the valves T-bolt has attached to his post.
Just so we are clear. I am by no means trying to discourage you from tackling this project. Just merely trying to inform you, your base head isn't a very good platform to invest that much time and effort into. Especially when you can accomplish the same thing if not better with hardly any to no work with a TB RH. Now if you were talking about another head that was a better platform to build more power out of...say a V2 head or +R head. I would agree it merits the time and effort to slam bigger valves in the ole gal. Good for thought any how
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Stormin, is there anything to be had angle milling the head slightly? Cutting a little more material off on the exhaust side of the head gasket sealing surface should put the intake valve at a slightly more vertical angle, to the cylinder. Maybe help the intake flow a little?
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3,191 Posts
Not really if there would be gains they would be very very minute and IMO it wouldn't merit all the headaches the would come along with the angle milling. The better route would be just straight mill the head. More compression (to an extent) builds more hp. The problem with this conception is more times than not a larger dome is placed to build that compression. With larger domes comes come cons. Larger domes weigh more plus larger domes are not as efficient as say a flat top or dished piston. The large dome effect flame propaganda which then gives you hot spot and uncombusted areas of the charge. The ideal route but not always easy to achieve with this mini hemi style combustion chamber is flat top and deck head til a good compression ratio is achieved.
Being your a machinist here are some thoughts that may give you more punch and all it will cost you is some wear n tear on tooling and a little bit of your time. Put the ole gal in a diet and start shedding rotating mass via flywheel and crank. I don't have any pics on hand of a 50/70 flywheel and and crank but here are some pics of a klx I recently did.
Most guys companies lighten flywheels like this
What I do and sheds off even more weight is turn od like seen above then jig flywheel up rotary table and machine the center step where the pick is just leaving the pick up behind like so
Actually found some 50/70 flywheel pics of before and after lightening I did. I could of been a little more aggressive with this one but 10oz isn't to shabby.
Moving on....if your comfortable with pressing cranks apart, pressing back together and truing. You can shed a fair amount of weight off the crank. The ultimate weight reduction is to reduce diameter of crank cheeks then pork chop them like so
Usually about now I get the well what about balancing. Well that has been a hot topic every time this gets brought up. I refuse to get in any more pissing contest over it so I will simply state where I stand on the subject, why, and say I have done many many many cranks and only balanced 1 and that one I sent out to be done by a big time crank company to prove my point to my buddies. all my personal engines has some degree of crank lightening done as well as all my good buddies I ride with and if you live close to new castle pa you are more than welcome to throw a leg over my bike and tell me you can tell it hasn't been balanced.
So where do I stand on the balancing subject and why. IMO spending all that time balancing is worth the very VERY small difference yielded from all the work. On multi cylinder engines say a small block V8 yes by all means balancing makes sense and is worth the hassle of balancing. On a single cylinder engine there will ALWAYS be a degree of vibration due to the lack of counter weight. With the bigger singles like the 250/450's they have counterbalancers which help but it is still there. As long as you get run out good you won't notice the difference. I once proved this point amongst buddies. I built 2 identical 50 engines and chassis only difference between the 2 (1) crank I just trued up run out the other I sent off for to be balanced. I didn't tell any of them I did this so feedback wouldn't be tainted. Upon getting crank back I assembled both engines and let the fun begin. We spent the day letting all of them throw a leg over each one. At the end of the day I then asked them some questions about which one felt like it had more engine vibration etc... Long story short not 1 single guy out of 8 could tell the difference. And this is why my opinion is so strong on the matter of balancing a single cylinder crank.
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