Topic: Stretching tank question...

[pddpimp]

Anybody out there ever enlarge their gas tank? Im looking to do so on a 69-76 750 tank.
I've see a few photos of tanks that are lengthened for the cafe look, but the space is not useable for gas. Im looking to get more room for gas. I'd like to make it good for at least 5 gallons, maybe even 6.

Thanks...

[754]

Do you want to stretch the middle or add to the rear?

[FunJimmy]

I'd love to find a streached CR tank for my CB550 project if anyone has one or would want to make one.

[pddpimp]

I think that I would like to stretch in the middle. I like the shape of the factory tank, so Id like to keep it as close to stock as possible. Im looking to be able to get 200 miles per tank. I like to travel, but hate stopping so much for gas. I understand and can perform the task, I just wonder if anyone has done it and what good\bad things the happened. My only fear is strength.

[okie]

FunJimmy, If you look closely at a CR tank, you will see that it's tunnel for the frame backbone is 2" wide at the rear.  Your 500/550 frame widens and splits into the two upper rear frame tubes.  That prevents the CR tank from fitting properly without MAJOR modification.

Ask me how I know.

Mine's a 350, but the frame design of 350/500/550 is very similar.

[FunJimmy]

Okie

That tank looks awesome! It it an Airtech?
How much effort would be required to fit a CB550?

Thanks

[okie]

Yes, it is an Airtech.  I cut 7.5 inches out of the backbone of the frame and welded up a new section that would fit the narrow saddle of the tank.  I believe Airech makes a tank that will fit your bike without modification.  Airtech quality is A+++++.  Good stuff.  They don't recommend using it on the street because in the event of a wreck the fiberglass will break and possibly start a fire.

[KB02]

The biggest issues that I can think of in stretching a tank are:
 - Leaks. Make sure you seal up the tank with your welds.
 - Fit. The stock rear fitment point will, obviously, have been moved and new mounting points will have to be fabed up.
 - Lines. The old standard tank has a really nice lines to it. Adding a stretch could interup those lines making the tank "look" like it has been stretch. Overcome-able, but something to keep in mind while you're welding it together.
 - Warping. If you're a half way near decent welder, you'll know enought to keep the seam cool enough to avoid warping as you weld it up. Otherwise your tank will be looking like waving sea.

Good luck. Keep us posted on your project and your progress.

[tinyrobot]

An easier approach might be to just move up to the later model tanks.  77/78 K tanks are 5-ish gallons.  Not sure about the F super sport tanks.  They have lines and shape similar to the earlier K models.

[Jinxracing]

Yes, it is an Airtech.  I cut 7.5 inches out of the backbone of the frame and welded up a new section that would fit the narrow saddle of the tank.  I believe Airech makes a tank that will fit your bike without modification.  Airtech quality is A+++++.  Good stuff.  They don't recommend using it on the street because in the event of a wreck the fiberglass will break and possibly start a fire.

Regarding the Airtech CR750 tank on a CB550...

I've been helping my neighbor with his '78 CB550K build and he decided to go with the Airtech CR750 tank and full fairing. Since we live close we took his bike down to Airtech and checked the parts first to make sure they'd fit. The tank is the "universal" version without the drop-down reservoir at the rear and it fit up perfectly. The only modification necessary was to trim about 1/8" off of the outside of each of the rubber tank mounting donuts. I'll see if I he has some photos of it in the mockup stage...right now it's in pieces; it just came back from the powdercoater.

The fairing turned out to be a really nice fit too...looks as though it was made for a 550 even though we ended up cutting holes for the stator/points covers. I can't imagine that fairing fitting around the (much wider) CB750 engine!

[okie]

You used the Airtech CR750 fairing on the CB550, or was it a different fairing? 

[Jinxracing]

You used the Airtech CR750 fairing on the CB550, or was it a different fairing? 

According to Dutch (the guy who we spoke to at Airtech), it's the Airtech CR750 fairing. The included mounts didn't quite work, so we had to weld a sliding tube arrangement to the steering head and modify the stock rear mount to work with the CB550 engine mounts, but it ended up working just fine.

You'll have to take my word for it though, since I was just over at his house and he has a few photos of it that he took with his cel phone, but neither one of us can figure out how to get the pictures from his cel phone to his computer. 

[wardmoto]

I hate to be so negative....but fiberglass is nothing but glass cloth and resin that when mixed with hardener...er...umm...hardends.  Modern gasolines will have their way with those tanks in a matter of time.  There is but one person in the country that builds a true CR750 replica tank based on original molds that is impervious to todays gasoline...and it aint Airtech.  Mike Medford  from Illinois was at the end of my exhaustive search.  The bottom line is, I got a CR 750 tank that is a dead replica that is impervious to todays toxic gasolines.  To ensure that, look up Bill Hirsch Automotive as he is the only one that makes an amazing tank liner suitable for fiberglass.  If you would like to talk to Mike, email me at bdward@ccpa.net.  Ps...He also did the seat pan. it is a CR 450.

[754]

I should mention , it is far easier to get a CB750 to get 50mpg than to stretch a tank..

Or you could get a trail 90 spare tank to mount somewhere.

If you must stretch thouh, I would cut just behind the cap area. Standing tank up and scribing a line with a surface guage would help..or a 2x4 with a nail in it.

Mount the 2 cut pieces on a plate and start forming a piece to fit in the gap.. be very careful and take your time. You could tack a few straps across to prevent pulling.

Forget about finding one piece trim for the bottom edge!!

[bistromath]

I have to say, ward, seems like any tank liner out there would work to seal fiberglass against gasoline.

[Jinxracing]

I hate to be so negative....but fiberglass is nothing but glass cloth and resin that when mixed with hardener...er...umm...hardends.  Modern gasolines will have their way with those tanks in a matter of time.  There is but one person in the country that builds a true CR750 replica tank based on original molds that is impervious to todays gasoline...and it aint Airtech.  Mike Medford  from Illinois was at the end of my exhaustive search.  The bottom line is, I got a CR 750 tank that is a dead replica that is impervious to todays toxic gasolines.  To ensure that, look up Bill Hirsch Automotive as he is the only one that makes an amazing tank liner suitable for fiberglass.  If you would like to talk to Mike, email me at bdward@ccpa.net.  Ps...He also did the seat pan. it is a CR 450.

Are you saying that the Airtech tank that my neighbor and I are putting on his bike is going to be eaten alive by modern gasoline and start leaking? Along with every single other person that buys and uses a fiberglass tank that wasn't made by Mike Medford? Your statement sounds a bit bombastic, but I'm willing to give the benefit of the doubt. Can you give more information as to why this is true, and more specifically, why Mike Medford's fiberglass tanks are impervious to this problem?

[okie]

I talked to Bob Hansen for about an hour about exactly these issues.  He is VERY knowledgeable and is easy to talk to.  He has developed several aluminum tanks and is working on a CR750 style tank for the smaller Hondas.  In the meantime, he uses Airtech fiberglass products.  Check out his web page.  Also check out the CB550 road racer he sold.  Cool!!!! 

I stole a lot of ideas for my bike from him;  and wardmoto, who has been my major inspiration to do my current build.

http://teamhansenhonda.com/forsale.htm


Here is a quote from Airtech Q&A page:

Can I use pump gas in your racing fuel tanks?
Modern pump gas is pretty crappy stuff. It contains a load of oxygenizers, fuel injector cleaners, ethanol, ketones and other additives that can wreak havoc on a fiberglass tank. Even though we use a high-end aircraft quality vinylester sealer on all of our tanks, it is possible a reaction may occur between pump gas and the tank liner.
We therefore recommend that anyone planning on using pump gas in any of our tanks first coat the inside of the tank with a fuel tank liner like Kreem, before putting gas in the tank for the first time. Heavily dilute the first-step cleaner in the Kreem kit, as it contains heavy ketones (MEK) that will destroy your tank. It is designed to remove fuel residue and varnish from a used tank. A quick rinse will do, do not let the solution stand in the tank, drain and flush with plenty of clean water.
Step 2 is the tank conditioner, since you're not working on a rusty metal tank, just swirl the solution around for a few minutes, drain and flush the tank with lots of clean water.
Make sure the tank is completely dry before proceeding and follow all manufacturers instructions with step 3, application of the liner.

Last but not least, always use a fuel filter.

Here's a good link to ALL of the Airtech CR750 stuff:

http://www.airtech-streamlining.com/hondaz/CR7501969-77SINCAM.htm

[wardmoto]

Do some research...not so.

[pddpimp]

I should mention , it is far easier to get a CB750 to get 50mpg than to stretch a tank..

Yeah, I understand what you are saying. I get 45-50 mpg depending on the ride and the weather.
I would just like to get 200 miles with out worrying about running out. I thought about the 77-78 tank, but...I just don't like it as much. I've been thinking about building an aluminum one, but I don't have all of the correct equiptment to finish it properly.

Thanks for the input

[bistromath]

"Do some research..."

well, i guess that ends any debate right there, doesn't it?

if POR-15 will seal your old steel tank and plug pinholes, it'll keep your new glass tank from ever touching gasoline, provided you properly seal it. if you have a used fiberglass tank and it's already damaged by gasoline before sealing it, no amount of sealant will cure it.

[wardmoto]

Epoxy resin v. Polyester resin.  Dig a little deeper... Are you building a track bike? Do you plan on letting gas sit in the tank when not in use?  If so, Airtech will be happy to take your money.  I am not anti Airtech, as I have used them often for other projects. But for me , there was no debate....$500 in the glass and another $500 in the paint...you can argue/debate with me all you want...if there are other members out there that are contimplating that expense, and they value a dollar like myself, I felt it was important for me to voice my experiences.  If your thoughts parallel mine, I will save you the time...Medford is all you will find; oh yea, I am not on the payroll.  I don't care to save a few hundred on a year long project that has consumed countless hours and many dollars not to mention the intangible emotional investment, only to find the tank melting a year later, taking my $500 paint job with it.  Thanks for the props Okie...I will help you any way I can.  By the way, Bombastic , is an adjective that describes one using or characterized by highsounding but unimportant or meaningless language...I was slightly confused by its use in one of the threads of this post as to me, it sounds as if someone was taking a shot.  I am here to learn and help, and I am not a member to satisfy an ego or to force my opinion on others...but based on the aforementioned defenition of bombastic, is it possible that the very use of that word in that post might indeed be....bombastic?? Man...that is good stuff!!!  I kill myself.

[754]

I think the correct term is,
"I SLAY Me !!!"......................

[Jinxracing]

By the way, Bombastic , is an adjective that describes one using or characterized by highsounding but unimportant or meaningless language...I was slightly confused by its use in one of the threads of this post as to me, it sounds as if someone was taking a shot.  I am here to learn and help, and I am not a member to satisfy an ego or to force my opinion on others...but based on the aforementioned defenition of bombastic, is it possible that the very use of that word in that post might indeed be....bombastic?? Man...that is good stuff!!!  I kill myself.

To clarify, my use of the term, "bombastic" was intended to illustrate what I perceived as the general intent of your original post about non-Mike Medford-built fiberglass tanks, not as a specific attack on your language. Based on your provided definition of the term, it still seems fitting to me. However, I apologize if I offended you...that certainly wasn't my intent. Hopefully my apology will help to smooth your feathers so that we can get back to the topic at hand.

What I was really hoping for was a clarification on the circumstances under which I should expect an Airtech tank to degrade when exposed to modern pump gas. Since your original post on the subject didn't include any information about tank liners and was highly critical of most available fiberglass tanks' reliability, I wanted to be sure that a properly lined fiberglass tank still had a reasonable chance of survival.

To make things clear, please let me know if the following line of thought is correct based upon your research and experience: Fiberglass tanks made by Mike Medford are safe to use with modern gasolines without the need for any sort of tank liner. Fiberglass tanks made by anyone else are likely to suffer damage of some sort or another if used with modern gasoline and left unlined.

[wardmoto]

Zero offense has been taken nor are my feathers ruffled....back to the topic. In my research, Medford's epoxy resin fiberglass tanks are impervious to modern gasolines and will not deteriorate.  He is the only one that I have found that does this process as it is apparently  very nasty and potentially detrimental to ones health.  On top of that, his tanks are true CR replicas of the 750 and 450 (among others).  Airtech and others do not use this process and have the potential to be effected by modern gasolines.  The chemistry was explained to me but I didn't bother remembering why as my choices negate any reason to rember these facts...  Sealing an air tech tank may help.  In my research on tank sealers, I ran into a lot of discrepancies with respect to POR and Kreem and others.  The only product that was happily applied to fiberglass and recommended was Bill Hirsch Automotive's tank sealer.  Would it work on an Airtech tank???Maybe.  My rational is that there are a lot of variables in the form of unaswered questions...."Will this work?  Will this leak? etc"  And I always end up with a maybe.  For damn near the same money, I got a handcrafted replica CR750 tank that will not leak.  I spent another 20$ on insurance and lined it with the only stuff I found that is forever OK on fiberglass despite not being neccessary...that 20 bucks reduced my stress level and was well worth it.  My tank looks like what airtech offers and will never leak, corrode, rust or turn to mush for the same money.  Clear?  Hope it helps, and again, it ain't my money...this is my opinion based off of my experience.  One last consideration...I had to fab the tank mounts and install dual petcocks...it took very little $ but a lot of time.  I took detailed pictures and notes on my install if you get that far and are curious...Good Luck

[Jinxracing]

Thanks for posting that info ward, I'll definitely look into Medford's tanks the next time around and be a lot more careful when it comes to picking what liner to use.