Head Rebuild or time for New Engine?

da1nonlysteven

da1nonlysteven

Member
Hello,

I have a 1973 CT70 K2 and it is come to the time when the engine needs a whole bunch of work after a couple years of hard riding.
After spending 100$ last year on a dumb valve adjustment,:102: I am looking to end all problems for years to come.

It needs:
-Kickshaft Replacement
-New Piston/Rings/ all top end hardware

The main reason for the rebuild is that the bike is hard to start and is very unreliable. These problems have come around because I have rode it hard. I am also looking for increased power in the engine as 70CC is not quite powerful enough for me.


My question is this do I rebuild the head, and put on a larger CC cover? And if so do i use the same carb?

OR:

Send into shop/ moto enzo?

OR:

Buy another third party engine?

I do have a mechanical knowledge and all the special tools and manuals, the part i dont want to mess with it the throttle, but taking apart the piston does not scare me, but getting to the kickstarter shaft, I know I have to crack the cases.

In the end I want a bike that is a little more powerful (110CC?) and a bike that is reliable and is the cheapest (Hopefully under 800$ CAD)

Thanks,

Steven Gill
Oshawa, Ontario, Canada
 
Under $800 probably just took enzo off the list.

Contact Racerx or Mark Pearson about a rebuild and have them put the 88cc kit in.
 
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Hi kamcrab,
saw your response on contacting racerx I'm new to your site and it looks like i need an engine rebuild oil coming out of spark plug.
 
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Are you having trouble with fouling the spark plug with oil? if so its uselly the rings are worn, can be valve seals, but if your having a lot of fouled plugs it's most likely time for piston and rings and boring the cyl. to fit the new piston. or up grade to a 88cc kit. Good luck with it,

Steven, you might contact fatcat on this site, he has engines for sale from time to time, seems not to long ago he had 88cc or 110cc at a good price.
 
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Hard riding should have less effect on service life than neglect & abuse. Dirty oil and dirt inhaled due to lack of proper air filtration take the top 2 spots for prematurely worn-out engines. With engines that have spent years, or decades, sitting unused, rusty cylinder walls are fairly common, too. Back in the day, virtually no one changed oil as often as should have been done; even fewer ever cleaned the oil spinner. Once the oil spinner is filled with clutch debris & metal particulates, the circulating oil becomes something closer to lapping compound - making quick work of cylinder walls & piston rings. The original air filter elements don't last forever, either. Doesn't take much sand to scar a cylinder. The only upper end part that seems wear-prone is the intake valve itself. The valve seat is typically unharmed, thus a new valve & quick lapping are oftentimes all that's needed to effect repairs. If your intake port is black, odds are the intake valve has been leaking for quite some time. Oil control issues almost always result from poor ring seal; bad valve seal(s) can be the cause, too. However, oil getting past the valve stem is mostly a secondary problem to scored cylinder walls. Sounds like your motor needs fresh cylinder wall finish (bore & hone), new rings, and a valve job. That will restore compression, cure the oil burning and bring the lump back to full stock power.

After a decent rebuild, there's no reason why one of these engines shouldn't be capable of mileage well into five-figures before needing another rebuild, with proper maintenance. The carb should probably be rebuilt and adjusted afterward. Although these engines usually won't run very well if the air:fuel mixture is way off, running pig-rich can dilute the oil with gasoline and cause heavy carbon deposits. Similarly, overly lean mixtures typically will result in weak running, however, if the mixture is right on the edge and the motor will rev-out completely, it'll run hot. That can burn valves.

As for the stripped kickstarter assembly, odds are both the shaft & arm splines are buggered. Starting technique can cause this. I've even seen kickstart pinion gears with teeth missing, the result of "slap kicking". That's just plain old numbnuts abuse. More typically, the splines strip out when the kickstart arm clamping bolt comes loose and remains that way. After the kickstart arm & shaft are replaced, just keeping the clamping bolt tight and applying a little basic common sense with your starting technique should make this a one-time-only repair.
 
Did some research and some e-mails here is my finding for all others.
ALL PARTS FROM MY TRAIL BUDDY ZEELEAND MI

Refit
Labour 400.00
Gaskets 20.00
Piston/Rings/Clips 80.00
Carb Rebuild 50.00
Clutch 50.00
Kickstarter 100.00

TOTAL 700.00

New Engine

Labour 440.00
Engine 325.00 ( 125 Cc Zongshen 4 spd man. elec start. 12V)
Wiring Harness 30.00
Footpegs 60.00
Conversion Adaptor 35.00
Electric Start Button 12.95
12V Battery 40$

Total W/Labour 942.95

Total w/o Labour 502.95

Resell old parts on ebay to gain cash back

I would also add shipping to my research because I live in Ontario. Another expense for me will probably be 50$ in chain + new rear sprocket.

I have done alot of research and I think this clearly outlines that for a daily rider, it is much more efficient to replace the engine and to do the work yourself. I am looking forward to tackling this project this spring and to have a good running engine for the summer.

Any cost that I have seemed to overlook?

Let me know,

Steven
 
Just me, but why on earth would you have them re-build your motor? Have RacerX, or Mark Pearson on this board do it for you, much more experience and knowledge of these bikes/motors. Stick with Honda base if at all possible. Just my .02
 
Well the reason why I priced a rebuild is because I wanted to compare that to a new engine. A new and more powerful engine has been on the to do list for a while, and since my bike stopped being reliable in the fall, I wanted to know what was I going to tide it over for the next season, until I am out of college.
I think I will put in a new engine and then hopefully the bike will be good for many years to come provided it is broken in properly.

Does anybody have experience with Zongshens Engines?

Steven
 
I think what Hymie meant was, why would you have My TB rebuild your bike instead of Racer or Mark who both are nationally known builders. Racer especially contributes a lot to this board and both have excellent reputations in the CT world.

As far as the Chinese engine, read the Chinese engine thread's here...Some people have good luck and some don't. A lot of times parts are extremely hard to find and I think most agree finding someone to work on them is very difficult. One thing that I have noticed is that the majority of the Chinese engine owners say if you are not mechanical to stay away from them...If you do have mechanical knowledge it is better, but you still might not be able to find parts very easy.

I have heard that the Zongchein? and Lifan are the two largest and have the most longevity...I have a Lifan in a clone bike I just aquired...I haven't had it long enough to really comment on it except it has 130 miles on it and no issues to this point....BUT, the valve adjustment nut on the intake side was missing. Luckily the bike had been babied and rarely used or it would have been a bad deal right from the start. If you do get a China motor, check everything on it before you fire it up and also change the oil that came in the bike before starting. I would also want to know exectly what the warranty covered and for how long.

FaatCaat and a_smereck would be good posts to read, both are very knowledgeable about the China bikes and have shared their expeiences. FaatCaat is a builder of the China hi performance motors. Personally, if I was you, I would have Racer or Mark rebuild your motor and keep your piece of mind.
 
I am not looking to keep it in stock or in showroom condition, I ride it alot, and I do alot of hard trail riding (Its hard keeping up with actual dirtbikes and ATV's ). There is a few of us who go riding quite often and I would like to be able to keep up. So that is why I am highly considering putting in a newer, more powerful engine. I may not sell all the old parts right away until I am completley satisfied with the new engine and sure that that is what I want.

Has anyone else got work done by those to? How much and what did you have them do?

Steven
 
Steven,

Let us know if you go with that Zongshen engine from My trailbuddy. I'm considering that same engine myself. I talked to someone at my trailbuddy about that very engine, and they claimed them to be of excellent quality. Of course, this needs to be taken with a grain of salt, since they're wanting to sell them.

Also take note, somewhere on MTB's site, they are doing a restore/mod with the zongshen engine, it it states that with this engine, you must remove and re-locate the side mounting bracket for the tail-light brake switch. You will also need either their aftermarket foot pegs, or slightly modify your stock ones.
 
Okay, now I know more about what you're trying to do and sounds like on a budget. If you just want more power to stay up with your buddies, go with the Lifan 140 or 150. Very powerful and cheap, so when it breaks, you can just chunk it and buy another. I'd suggest the 140 since I hear 150 parts are difficult to source. FWIW.
 
da1nonlysteven said:
Will do, but the funny part is he told me that it did not have to be relocated, because that applies to the 155 cc version.

Steven
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Take a look at this page. They are showing a Zongshen build that they are working on. About 1/3 of the way down, they mention it.

Trail Buddy, Honda CT70, Trail 70 bikes & CT70 parts


Although, that page has been on their site for a while now, and the zongshen engines they have now, are relatively new, so maybe it changed? I dunno. This is what I hate about these Chinese engines. They're tempting, but it's next to impossible to get decent information on them.
 
Haas said:
... and the zongshen engines they have now, are relatively new, so maybe it changed? I dunno. This is what I hate about these Chinese engines. They're tempting, but it's next to impossible to get decent information on them.
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There are some good questions and some good points in this thread. But, as frequently happens when discussing this topic, it's turned into blurred comparison with more gaps than head-to-head data.

PRC motors are going into season #10. The only constants with these is that there are no constants. They are cheaper than ever and, to date, none has remained on the market, unchanged, for very long. The old Z108 was the best built Chinese lump we've seen but it's long gone. No idea how it stacks-up next to the newer Zongers and until the 2012 season it will remain a mystery for most. How can one make a informed decision without a field service record? Odds are overwhelming that these "latest & greatest" engines will be orhpans by then. FWIW, the Z108s sold circa 2001, came in 2 very different versions and even the better of the two left a lot to be desired, especially if you're expecting OEM Honda-like operation, durability and parts support. Dealer wholesale was more than double the retail price of the newer units and that's been the real story since at least since the `04 season, when the race to the bottom began in earnest. If you want the cheapest horsepower available, made-in-PRC has the crown. If anything else is important to you, then Honda-based is the better way to go. Question: how many Honda engines came with rubber clutch springs?

Put it this way, Honda engines have been available, with parts support, for many years now, plus a 40+ year field service record. If they were trouble-prone, you'd know about it by now. Mileage is a dividing line. If you don't plan to ride more than a couple thousand miles, total, then a cheap motor could be the way to go. On the other hand, if you plan on keeping the bike for more than a couple of seasons and riding 2000+ miles annually, then investing in quality parts will pay you back. It may even work out cheaper on a per-mile basis. Pretty well everyone understands that higher-than-stock output is an engine stressor. That said, hardly anyone stops to consider that total mileage and extended running are stressors, too. Building an engine that runs smoothly & reliably for thousands of miles is every bit as important to a serious road rider as building for big HP is to a racer. It's just not a glamor subject that comes with bragging rights...like mph. Of course, waiting by the side of the road for "captain hook", then sitting out weeks of riding season working out the details & cost of repairs for a broken engine doesn't' exactly come with glamor & bragging rights either. Figure out what your top priorities are, then build toward realizing them.

A typical engine rebuild, done right, takes ~$300-350 in parts and machining. That includes new valves & valvetrain wear items, cylinder overbore & piston kit, oil pump, clutch discs, valve job, points, condensor, gaskets & seals. That number can move a bit in either direction, depending on the motor. Once the cases are split, replacing a kickstarter shaft assembly is a $50 proposition, including new C-clips. If one is capable of doing the teardown & reassembly, then installing a stroker crank & big-bore upper end are no more difficult than reinstalling the stock parts, making 110cc - 120cc a long weekend's project. Hondatrailbikes' 110 & 117cc kits are some of the better values out there and have been around for some years now. Add one of their HD billet clutches and an aftermarket 12v CDI conversion (search the old threads for the ebay seller, or ebay directly) and you'd have a 55-60mph cruiser, that even appears mostly stock. Top speed potentials are higher. A 3-speed tranny might not be your first choice, but they're strong and shift well, as Honda trannies do. The rest of the 12v conversion involves little more than a 12v battery & bulbs.
 
racerx said:
A typical engine rebuild, done right, takes ~$300-350 in parts and machining. That includes new valves & valvetrain wear items, cylinder overbore & piston kit, oil pump, clutch discs, valve job, points, condensor, gaskets & seals. That number can move a bit in either direction, depending on the motor. Once the cases are split, replacing a kickstarter shaft assembly is a $50 proposition, including new C-clips. If one is capable of doing the teardown & reassembly, then installing a stroker crank & big-bore upper end are no more difficult than reinstalling the stock parts, making 110cc - 120cc a long weekend's project. Hondatrailbikes' 110 & 117cc kits are some of the better values out there and have been around for some years now. Add one of their HD billet clutches and an aftermarket 12v CDI conversion (search the old threads for the ebay seller, or ebay directly) and you'd have a 55-60mph cruiser, that even appears mostly stock. Top speed potentials are higher. A 3-speed tranny might not be your first choice, but they're strong and shift well, as Honda trannies do. The rest of the 12v conversion involves little more than a 12v battery & bulbs.
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I would be more than willing to do these conversions myself, it would be my father (Mechanical Engineer) and me, and it would probably take a little longer than you pros :4:
I looked on their site racerX and could not find the kits you were talking about. I looked under the CT70 section. If you could show specifically I will probably use that as my option.

However if someone was willing to do all the work for me and upgrade it for 110-120 cc I would be quite pleased to put it into the hands of a pro for a few weeks. I just need to know costs. Also converting to 12V would probably be a good idea. I would even be willing to pay for you to buy parts and I would reimburse the fixer. I guess my only goal is to have it up and running by mid april.

Thanks,

Steven Gill
 
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