Had the same problem on my last rebuild. It was not a valve hitting it was the piston hitting the head gasket. I had a lot of s65 gasket kits (same except for the head gasket) from past rebuilds thought I would save buying a c70 kit. The head gasket looks like it will work BUT it is just small enough to stop the piston at top dead center. Did you replace the piston when you tore it down? was it the correct dome top? with the cover off on the top of the head you can see if the cam is on the bottom of the stroke (lowest part of the cam lobes)the valves should be closed if not you have a valve hanging up. If you got it to cycle and fire before the teardown the problem should not be a valve hitting. A valve lap may help raise the compression.
--- In Honda-C70@yahoogroups.com, Ken Teng <k.teng@...> wrote:
>
> Thanks Baby Huey for responding, my Passport is a 1981, I did the compression test before I decided to remove the head. The bike would fire up a bit chug chug backfire when I put some gas in the spark plug hole. The compression is supposed to be about 175 psi. I only got max 125 psi so I decided that it would be good to remove the head & take a look. Following the manuel for engine tear down I lined up the 0 on cam sprocket to 9 oclock position (V-grove on head) & Tdc mark on ignition advancer (on crankshaft) to arrow at 11 oclock on stator. It appeared that the timing was not correct so I mucked with it but was alittle unsure that this was the problem. Turned over by hand & valves were hitting pistom now. Have removed the head now cylinder bore looks good but I think that I will probably lap the valves.I did not no that there is a mark on the timing chain as well the manuel didnt say anything about that or maybe I misread. Thanks for youre
> help, Ken
>
>
> From: myron andrews <mvandrews13@...>
> To: honda-c70@yahoogroups.com
> Sent: Wednesday, June 15, 2011 9:13:13 PM
> Subject: RE: [Honda-C70] Engine timing issue.
>
>
> Ken : You mentioned the cam sprocket mark but not the 0 on the cam chain. The 0 on the chain & the 0 on the cam sprocket both should be together at the tdc on the head [that is 9 o'clock position on the bike ] & both valve tappets should be off [valves closed] the valves ends . Other than the cam chain on the wrong tooth at the crank shaft I can`t think of a way for the piston to hit the valves. I take that back down shift from 25 mph in 2nd gear to 1st gear by mistake made my piston & valve hit. But then I had 0 compression. I think we need more info on your bike , year, c70 or clone motor with timing in the head rather than on the crank. How did you get a compression check if the piston hits the valves? Good Luck !
> Baby Huey
>
>
>
> To: Honda-C70@yahoogroups.com
> From: k.teng@...
> Date: Thu, 16 Jun 2011 02:42:46 +0000
> Subject: [Honda-C70] Engine timing issue.
>
>
>
>
>
>
> Hi I was wondering if anyone out there could give me some help with a mechanical timing issue.I allighn cam sprocket mark with mark on head advancer tdc mark with arrow mark on stator.I am following the mannuel but my piston now hits the valves.I have never had this bike running so I am wondering if someone has replaced the advancer with the wroing one.I was also womdering if 115 lbs. compression when cold would be enough compression to make this baby fire.I would really appreciate any help. Thanks Ken
>
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> [Non-text portions of this message have been removed]
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> ------------------------------------
>
> C70 Passport Not Running Right?
> 1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
> 1970-73 C70 Troubleshooting Guide:
> http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
> 1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
> 1980-81 C70 Troubleshooting Guide:
> http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
> 1982-83 C70 Troubleshooting Guide:
> http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
>
> 1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
> 1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
>
> More resources for C70 Passports and Cubs:
> http://www.shlaes.com/Vehicles/Scooter.htm
> http://www.velodrome.com/HondaC70/HondaC70.htmlYahoo! Groups Links
>
>
>
> [Non-text portions of this message have been removed]
>
1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
1970-73 C70 Troubleshooting Guide:
http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
1980-81 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
1982-83 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
More resources for C70 Passports and Cubs:
http://www.shlaes.com/Vehicles/Scooter.htm
http://www.velodrome.com/HondaC70/HondaC70.html
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