Sticking a Honda Hot Cam (or DRATV Mini Monster Cam) in a stock 3-speed CT70

[kawahonda]

Racerx thinks it's a good idea, and I do trust him. Gaining a little bit more top end and pinching off a few more MPH without a loss of low-end is the goal.

Have any of you done a cam-swap to the Mini Monster (or Honda Hot Cam) on a stock CT70?

I found one post where one person did it, and said that the bike is probably slower and he lost low end. I found others who have said the opposite. Is this a safe bet swap? Better cam all around.

 

[OLD CT]

I would just take the head off, there are more pros than cons, for my reasoning. Is that a deal breaker, if the head has to come off?

Jeez, how does sidewinder post them friggin epic novels??????????
I got Fing timed out 2 times trying to post my response! Obviously, I must type slow... BWAHHHAHA!

 

[kawahonda]

Bwahaha.

No, not a deal breaker if the head has to come off. Would like to keep the engine installed. If it's just a cam swap, isn't it just as easy to just pull out the cam with the head still on?

Or are you suggesting to just replace the head along with the cam?

But all in all, can I count you as a "yes" vote for benefiting from mini monster cam over stock cam?

 

[OLD CT]

Yep, I was pretty pissed getting timed out. The problem is I can NEVER word anything the same, the second time!

I like to take it off because then you can look at evertyhing, very close.
Dratv's aftermarket rock set are great and I never like to just put a new cam on old 40 something well ''worn in'' rockers.

You can get a better look at the cam journals for wear, if you can catch your fingernail on a groove, then change it. I like the stock heads and would keep it, if it checks out. You can de carbonize the combustion chamber and piston top. Then I would also do a leak test on the valves, while it's off.

Lastly, I really think trying to ''just stab the cam'' in will take some finesse and I had to actually push on the rockers with the nut and adjusters all the way off with my fingers! PITA! ''time waster'' and then turn it 9 ways from Sunday to get the damn thing in! The Rubix Cube was never ''my cuppa java'' He he!

the list..... head gasket, new aftermarket rockers and the cam. Just make sure you don't need the ''front'''rocker cover gasket before you order.
Better yet take it apart before you order.

 

[kawahonda]

Thanks OLDCT. I'll put this on the "to do list" for an upgrade...

 

[OLD CT]

Almost forgot, you WILL like it for blazing to work on the street.Lol!
It is a nice subtle increase. Like Bob said you will notice you can rev it more and that's where you will find your gains, with no loss that I am aware of down low.

 

[kawahonda]

It won't change its "off-road ready-ness" will it?

If the head comes off, would it be worth lapping the valves? Changing the valve guides, etc?

Trying to think a head a little bit.

 

[69ST]

It won't change its "off-road ready-ness" will it?

If the head comes off, would it be worth lapping the valves? Changing the valve guides, etc?

Trying to think a head a little bit.

With the compression readings you posted, I wouldn't touch the valves unless the intake port is turning/turned black. I am under the impression that this engine is in tip-top shape and with low mileage. If you're going to pull the head and replace the rockers, don't be a piker...replace the cam chain, roller (inside the cylinder tunnel), idler & tensioner piston cap while you're at it. If the rockers have visible wear the rest of the timing chain assembly will be worn, too.

If it's time for a valve job, it's probably time for new valves, too. It's pretty rare to find valves with contact bands that aren't worn across the entire valve face, top-to-bottom. Just doesn't sound to me like you have a valve problem, at this time.

Valve guides rarely wear out in these motors. Replacing them requires a special driver and guide reamer.

 

[kawahonda]

Yeah. Because my engine is in excellent shape...155 PSI COLD compression at 2800ft elevation, just makes me want to swap the cam only and leave the head alone. It's not like we are dealing with a high mileage or worn bike here. I think the mileage is 1200.

 

[fatcaaat]

You do not need to remove the head to swap a camshaft. You have to loosen the tappet adjusters all the way loose and then hold them open and pull the cam right out. As for improvement, yes, you will gain a little more top end and maybe a little more usable power in the 5-7500 rpm range and probably won't notice anything missing on the bottom. You may need to adjust jetting. I don't see any way possible that you would have less speed/power from adding a cam if you also dialed the engine back in. For something that is stock everywhere else, adding a huge cam probably isn't going to get you any massive gains. If you want to really get improvement, you'd need to port it, exhaust it, and carb it most likely.

I've posted before that by adding a supertrapp, vm20 and portwork, I was able to have a very noticeable improvement in acceleration and I was able to regear the bike to go 50+ on a flat. But all things being equal, I think you'd be better off adding a 52mm bore kit and rejet and achieve the same thing with everything else stock.

 

[kawahonda]

Thanks Fatcaat.

Right now, I am lucky to have an exhaust gas analyzer in my possession. So tuning is pretty darn easy for me. With the stock 58 main, I actually have plenty of "richness" available on hand. Currently, my needle is in the second to leanest position and I’m well into the rich zone at WOT. I wouldn't expect doing any more than maybe raising the needle up one notch with the new cam, at the most, then re-setting the air/fuel mixture at idle to achieve a balance.

Sounds like this cam is a go. It's a done deal! Not looking for massive gains here at all. Just setting myself up for success later down the road if I wanted to go further. And if I get 2 more MPH for $46 at no loss, then I'd grow a big fat smile on my face. When you're at 38.5 maximum and then move up to 40, it makes a big difference on a 35MPH road. In-fact, 40 sounds about as fast as I would ever need to go on this bike where I ride it. PLUS, I need to play around with the points gap setting to see if advancing it a little bit would wake it up even more.

The nice thing about a cam swap, is that it doesn’t really require me to do anything else. The 88cc kit does require more to go along with it, such as a high volume oil pump. Then you need a bigger carb. Then you gotta remove the baffle out of the pipe. Then you should replace the air box. It turns more into a "package" deal. I feel that the cam can be a "hit it and quit it" approach without feeling on the need to replace more because "this" and "that" is now lacking. Hopefully that makes sense.

Another way to say it is that this cam seems to MAXIMIZE what is currently there. I'm totally fine with that, and am totally fine with 40-43MPH.

 

[69ST]

Another way to say it is that this cam seems to MAXIMIZE what is currently there. I'm totally fine with that, and am totally fine with 40-43MPH.

This puts things into clearer focus. Once you've gotten the carb dialed-in, the cam change should give just what you're looking for ~3mph. If if you consider the math, that's roughly a 1hp increase, pretty good for a simple cam swap, imho.

In general, with small bikes and marginal power (especially torque) seemingly small differences in output and gearing can have bigger results than intuition might tell you. 300-500rpm difference another 2-5mph can make all the difference between being just to the high side of the success line, and enjoying the results...and coming up just short, with endless frustration. This also applies to a "stingy" speedometer, one that reads slower than actual speed. It's part of the gearhead's curse.

The H.V. oil pump isn't strictly necessary but, you're going to be giving this bike a pretty vigorous workout, so the added cooling can only be good.

 

[OLD CT]

I actually did the opposite of you. I put a 88 kit I purchased on e bay cheap. 65 bucks was the winning bid I recall, and left the head all stock, no hot cam or head porting with the stock carb. It has a free flow pipe.
I did have to replace a bent intake valve and probably why the bike was parked DOA. It runs pretty good but don't want to bring it to full speed yet. I figure low 40's maybe 45 after a mile.

Almost forgot. No hi vol pump on it, there is a big oil cooler on the side of the head to keep break in temps lower. 16-35 sprockets.

 

[kawahonda]

Hmm, good info. I'm really considering the 88cc kit, but I feel that I would have to open a new door into the "unknown" of just buying more stuff and making my CT70 look not as-stock as I would be trying to "chase the dragon".

I figure if I ever find a cheap ass CT70 for sale that didn't have good original parts that I would use that as a hopped-up 88cc beast and would have no problem sticking as much aftermarket stuff on it as possible. But my K3, I try to respect it's originality as much as possible...try to do as much "hidden under the hood" type things as possible.

That's why I think I'm a big fan of just doing the cam swap to begin with. One could keep a semi-straight face with the mini monster cam and say that it has the Honda "European" grind cam without many frowns. For someone who is wanting a little more street oompf without "going down the rabbit hole", it seems like a good idea to start that route first.

If 50 MPH is what you're after, then fire up an excel spreadsheet and get planning because you'll be doing the whole "shibang"

But I'm only after a little bit more. 40-45 MPH is really all I ask for based on my use of the bike, which is driving it a mile to work on a 35 MPH road.

But that's how it always starts, right?

Right now, as is, my CT70 cruises confidently at 35MPH. Anything more requires me to lay down on the bike, ignore my mirrors, and soon I would get up to 38.5MPH (which on my CT70's speedo is an indicated 35) tested on a .7 mile stretch. But again, I will be trying Racerx's point trick this weekend to maximize this further. I have YET to see my speedo hit a "40". I will take several shots of whiskey when it happens. I also will be replacing the rear wheel and sprocket/chain with a new stuff this weekend as well. For now, I feel confident in ignoring the 16T sprocket that I purchased and decided to stick with the 15T.

I've came a long ways. The bike couldn't start when I got it. Then it would hit 20 MPH, tops. Then after months of tuning/fixing, it did 27MPH. Then 33MPH. Then 38.5 in .7 miles recorded by my father in a new Ford Escape. I've came from zero to hero!

And I ain't done yet!

Racerx....one more calculation if you can...for a .7 mile stretch, a stock CT70 should do_____MPH @ WOT.

 

[kawahonda]

Cam ordered. Plug and play. If you have a good pictorial guide on a cam swap, please let me know.

I won't be doing a cam swap for a few more weeks. I want to try to maximize the speed as much as possible BONE STOCK before doing alterations of any type.

"one thing at a time", right?

 

[fatcaaat]

These engines, are for sure, bulletproof. But I'm thinking about what you are asking it to do. You are looking to run it on a 35mph road, 40+ or so mph. Essentially, you are looking to run this bike, max speed (not cruising speed) for a period of time on this road. Other way to think about this, you are going to run this engine flat out in the redline. I would have to think that would be very abusive, even to this engine, to run it at like 9000+rpm for extended periods of time. I'd say that if you wanted to get maximum life from a stocker (or even with your cam) that your cruising speed would be no more than 35mph and I might even say its closer to 30. Running it ragged the fastest it will go will absolutely shorten the life of everything inside that motor (except maybe the transmission gears and non-moving parts)

I had a kid purchase a chinese 70 pitbike from me...one that was in excellent shape and the motor was basically new. He was going to use this bike to run up and down a 6 mile stretch of a paved path to and from his girlfriends house. I dialed it all in perfectly and fit it with a quiet exhaust and jetted it so it was excellent. We put a bicycle speedometer on it so he could see how fast he was going.

About 2 days later, he brought it back to me telling me it won't run. I asked him what happened and he told me it quit on the 3rd trip. I asked him about how he was riding it and he told me he had it pinned...for pretty much the entire trip in both directions. ON the third trip back, it floated the exhaust valve and kissed the piston. I took it apart and replaced the valve for him free of charge (it took less than an hour) and I told him that the bike's cruising speed was about 30mph and if he went any faster than that it would happen again and I would charge him to fix it. He texted me about 6 months later telling me the bike was still running perfect, making about 3 trips a day...that's 48 miles a day on it. He also told me that he never runs it faster than 30mph (this one is even a 4-speed).

The point is, that anything you run above 70% of max speed for extended periods of time will dramatically increase wear/tear and reduce longevity of an engine.

 

[kawahonda]

Interesting info Fatcaat.

I know that running the Honda Twins and Fours high RPMs for expended periods of times (but not in the red zone) is A-OK! I wouldn't suspect the CT70 to be any different, unless you are going into the red zone, of course.

My full speed stretches are going to be .7 miles at the most, and back, and only maybe once a week at the most. That's a bit less than 6 miles daily. Maybe having HD valve springs is a good idea, regardless. Lots of variables here, though.

Based on my limited use, I'm not too worried about stressing that CT70 motor.

 

[69ST]

I tend to agree with Jarred on the somewhat arbitrary "redline" of 8000rpm, for sustained cruising. 7/10 of a mile doesn't constitute sustained cruising, imho. There are a number of variables, valve spring fatigue isn't among them. Aside from the fact that a stock CT70 motor reaches peak output at ~8000rpm, the most critical factor is heat. Pushing an engine beyond it's power peak over a sustained distance, IMV, means the bike is under geared and wasting revs per mile. Break out the calculator...an extra 500rpm, at 30mph, means an additional 1000 crankshaft rotations per mile, 100,000 per 100 miles. That's a lot of wasted motion.

Keeping oil & combustion chamber temps under control is what matters most. I doubt that you'd float a valve below 10,000rpm and a stocker isn't going to make power up to that rpm. Thus, you'd do better to install a H.V. oil pump, instead of H.D. valve springs. The increased oil flow aids cooling. Honda upsized oil pumps with the newer motors. The Wave 100 & Nice 110 oil pump is ~4x the size of a Z50/CT70 pump. I've run my 110 Nice-powered bike wide-open for 20-30 miles at a stretch, no problems, oil temp never exceeded 102C. I also prefer to keep the main fuel circuit a little on the rich side; this is why.

 

[kawahonda]

Oil pumps replacements do require the engine to be removed, correct?

OLDCT, I kinda like that cooler you have...is that still available?

EDIT: took a look at Tbolt's site and they had a nice pictorial guide for HV oil pump replacements. It's definitely involved and looks like the cylinder needs to be pulled. Good idea for down the road.

 

[OLD CT]

The G-Craft oil cooler is available but it will not fit your head. The engine it's on is a 1982 CT, the first year for the head design change...
The price is $150. It was purchased for another CT70 er 124cc with a race head. I am only running it on this bike temporarily, for break in purposes...
This engine is the lowest budget engine to date. It ran me under $100 in parts total to bring it back from the dead. And looking forward to letting you know just how fast it will run, after some miles. $65 dollar shipped 88kit, 9 dollar shipped 16T, 1 intake valve ''free'' in the parts from the previous owner and 14 dollar clutch fibers is all she wrote. I think 45MPH is doable!

Almost forgot, I didn't even have to take the flywheel off yet! The bike had spark but would not turn over properly due to the bent valve.