Hard to start 1970 trail 70

[Steven E Vale]

I installed new fuel
Lines, cleaned the carb (looks like repro from Dr. ATV, cleaned points, set timing, valves. Good spark. Compression is low at 85 ish. It does not smoke.

your thought on the hard starting? Usually about 8 kicks.

 

[69ST]

Wow...that's really low cranking compression. I'm a little surprised that it fires, tbh. If compression is really this low, not just a false reading (very hard to avoid with small displacement) then power will be way down, too. If the engine has a tough time pulling you along at 30-35mph, that's a good indication that it's time for a valve job. A healthy engine should have no trouble reaching 35-40mph on the flat. The intake port is a good diagnostic tool, too; if the intake port is blackened, there's confirmation of a leaking valve.

 

[Steven E Vale]

If I pull the head to look at the valves, should I go ahead and install new rings? I’m assuming the cylinder and piston look ok?

Should I order just new valves or a new head with the valves and from whom? I don’t have a valve compression tool or lapping tool and materials like I Used to.

my old Honda book says 153-187 PSI.
Thanks, Steven

 

[lukelaw1]

Is the intake port clean aluminum? As racer was saying if the intake port is black then your intake valve isn't sealing properly and your loosing compression through the intake. You can also set the head on the bench with combustion chamber facing up and fill the combustion chamber with a light weight oil or etc. let sit for a minute or two and check the exhaust and intake ports for fluid. No fluid=valves are seating properly and time to move on the something else.

 

[Steven E Vale]

If I pull the head to look at the valves, should I go ahead and install new rings? I’m assuming the cylinder and piston look ok?

Should I order just new valves or a new head with the valves and from whom? I don’t have a valve compression tool or lapping tool and materials like I Used to.

my old Honda book says 153-187 PSI.
Thanks, Steven

 

[Steven E Vale]

I assume it would be either valves and or the rings. I’ll start with valve leak test. I thought if rings it would be smoking as oil getting by.

 

[hrc200x]

Does the cylinder and head look original or recently replaced? If look newer the cheap China complete top end kits on ebay when installed on the old bikes usually have compression around 80psi.

 

[Steven E Vale]

No it looks original.

have you used Dr. ATV for parts? I’ve bought a number of things from them, just not engine components before. Thanks!

 

[hrc200x]

Dr. ATV as in beatrice cycle in the midwest, Nebraska possibly, is a good vendor, there is a ebay member thats user name is something like DR_atv_411, that sells new cheap ct70 parts that seems to be one to stay away from

 

[Steven E Vale]

Yes, that’s the business in Nebraska that i have purchased parts from.

 

[69ST]

If you remove the head, inspection is easy. Set the cam so that both rockers are one the base circle, or pull the cam. That way, both valves are fully closed. Shoot brakleen into one port, enough to create a small pool around the valve. If there's any leakage, you'll see the solvent coming through, creating wet spots inside the combustion chamber, around the valve. The solvent has extremely low surface tension and it'll "find" minuscule leaks.

The fact that you're not seeing oil smoke, suggests that the cylinder walls & rings are still okay. A proper valve job consisting of new valves, seat cutting & lapping, plus a new stem seal, might be all that's needed to make the top end assembly right...and restore full compression.

 

[Steven E Vale]

I was a Honda motorcycle tech back in the mid to late 70's. I went to the Southern training center in Atlanta. I worked for several Honda motorcycle dealers in Tampa while going to college. They had all the special tools. Any suggestions on how to tackle? I vaughly remeber the steps, just don't have the tools to perform the work. YouTube has helped stimulate my memory.

Thanks for all the great advice.

 

[69ST]

I was a Honda motorcycle tech back in the mid to late 70's. I went to the Southern training center in Atlanta. I worked for several Honda motorcycle dealers in Tampa while going to college. They had all the special tools. Any suggestions on how to tackle? I vaughly remeber the steps, just don't have the tools to perform the work. YouTube has helped stimulate my memory.

Thanks for all the great advice.

The "brakleen" leak test is just a refined shadetree mechanic process that is very reliable. Re-cutting valve seats is more art than science, especially with these cylinder heads... because there's not much working room. It takes a long time to accumulate sufficient experience to do the job quickly & efficiently. Cylinder boring is far more science than art; mastering that takes even more years of experience and a 5-figure investment in equipment. As for everything else, there are a few quirks with these engines and a few specialty tools needed. You probably have way more than enough basic knowledge to learn you way through the <slightly> tricky stuff. The only specialty tool needed to tear-down & assemble a cylinder head is valve spring compressor.

It's the lower end that requires the bulk of the specialized tools: clutch socket, impact driver + JIS bits, flywheel puller, snapring pliers. And the only process that will have to be farmed-out is a crank rebuild, which usually isn't needed.

 

[Steven E Vale]

I’ll try the brakleen test first. I have some of those tools. I found a flywheel puller in my tool box from Honda and used it the other day to pull the points and set the timing.

I assume I could buy a head for it from Beatrice cycle that would work?

great info!

 

[Steven E Vale]

 

[Gary]

Steve these valve springs are not all that strong- you can make a tool using a piece of the proper size electrical conduit with notches cut out to get to the keepers and a large C clamp. There used to be a site that showed you how to make these tools but it's unfortunately long gone. Old Honda shop manuals used to show how to test valve sealing with fluid in the chamber and air pressure in a port but I cannot remember what fluid they used. If anyone likes reading and learning pick up an oem copy of an S65 shop manual. Since those were the first use of that style Honda engine they are really detailed.