Did you run it out of oil?
If just low, you might just have a loose cam chain. You need to drain the oil and measure how much caame out,
run a magnet in a plastic sack thru the drained oil to check for metal particals.
Then when you add oil, check and double check how much goes in when the dip stick says full. Then run the engine
and recheck the oil level ( you only need to idle it for a few minutes) then recheck the level, if it droped
by much (you are checking with the bike held vertical and only setting the dip stick into the hole ,not screwing it in, right???)
I would think the oil passages are plugged in the crankcase thst allow the oil to free flow between case halfs.
From: Jean Luc Picard <firstname.lastname@example.org>
Sent: Sunday, October 16, 2011 7:08 PM
Subject: [Honda-C70] engine rattling
I was riding my bike at around 45mph when it started overheating. I bought a quart of oil at a nearby gas station & got it going again but now there's a rattling when I rev the throttle. What happened?
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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: