Compression tests on cylinders

[jamestnewsonr65]

So after a few problems starting my bike (Recent posts) it turned out to be a combination of spark plugs, battery power and needing a general tune up.

The timing was slightly off, but all is working well now and the bike fires up nicely.

I did a compression test to see if this was part of the overall problem and I got results of 55psi on the left and 80psi on the right.

Should I be looking to check the piston rings and tube seals?

I checked this by removing the 3 pin lead under the front cover, removing the spark plugs and then fitting a compression tester to each cylinder whilst cranking the bike for 2/3 times.

From memory the PSI should be over 120psi at least, so this is a little concerning.

Any advice appreciated.

[wilcom]

Did you hold the throttle wide open?

[Bob_Roller]

You need to get at least 10 compression cycles to get a proper compression test .

You can stop when the pressure on the gauge doesn't go any higher .

As wilcom has said the throttle needs to be held full open during the test .

[Tony Smith]

The timing was slightly off, but all is working well now and the bike fires up nicely.

I did a compression test to see if this was part of the overall problem and I got results of 55psi on the left and 80psi on the right.


I checked this by removing the 3 pin lead under the front cover, removing the spark plugs and then fitting a compression tester to each cylinder whilst cranking the bike for 2/3 times.

From memory the PSI should be over 120psi at least, so this is a little concerning.

Firstly I'd be buying a new compression tester. Whilst an R65 engine might run with 50~60 psi compression, you would need ether to get it started.

Whilst I applaud the thought that went into disconnecting the beancan, that didn't really stop the coils from being charged up - next time simply disconnect the positive lead to the coil - which as an added bonus, does not require the removal of the front cover :-)

In respect to checking over rings etc, my question is "how well known is this bike to you?". If it is an unknown that you have just restored to life then I would have checked valve guide clearance, had a look at valve sealing and, give the relatively low cost, probably thrown new rings (and if an iron bore a de-glazing hone) at it because then I could restart the "counter" to when I next needed to look.

On the other hand, if the bike is known to you and the distance  since last top end refresh is around 50,000km (30,000m) then I'd do the top end refresh irregardless of inspected condition. OR, if it is more than 5 or 6 years since the heads were last off irregardless of mileage.

It may be because the wife's original R65 engine was destroyed by dropping a valve (at 60,000km and 9 years since new) or that my own R65 came to me as a result of dropping a valve (at 52,000km and 10 years) but if I take the heads off an airhead these days I replace at least the exhaust valves - they are cheap compared to new head/piston/cylinder and although I have no "proof" I reckon combustion tempos are a bit higher on unleaded fuel.

[jamestnewsonr65]

Not sure I had the throttle wide open to be honest. I'll try it again and make sure I do.

I've had the bike for 3 years and restored it apart from the engine. It had been regularly serviced and I have every receipt since new. Covered 18000miles and runs fine. No smoke, oil or anything burning/ leaking.

[jamestnewsonr65]

Here's a pic for the hell of it.

[Bob_Roller]

Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

[Tony Smith]

Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - 44 years? Which parallel dimension is yours in?

[Tony Smith]

Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - that may be the case in your dimension, but in mine I think you will find that mandatory unleaded fuel didn't commence until the 80/90s.

[Tony Smith]

Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - 44 years? Which parallel dimension is yours in?

bod, sorry for the multiple messages - the forum is going crazy here and i thought my original post went directly to cyber cemetery.

[Matt Chapter]

mandatory unleaded fuel didn't commence until the 80/90s.

40 years, 30 years, it's all the same once you get up there.

[Justin B.]

The first new car I bought was in 1973 and it had to run unleaded - right at 44 years.  Remember, young'uns, there are some of us around that actually had to put up with that kind of crap...

[Bob_Roller]

Starting with the 1973 model year vehicles made in the US, unleaded fuel has been mandated, the fuel filler, had a reduced diameter hole, so regular leaded fuel could not be used .

Adapters were sold, that you could put on the fuel filler nozzle, to reduce it to the correct size for use with leaded fuel, but people found out that the lead contaminated the catalytic converter to rendered it useless and it had to be replaced, when you had to go mandated exhaust emissions testing that started shortly afterwards, as part of the yearly vehicle registration progress .

Up until 3 years ago, we were required to have motorcycles exhaust emission tests every year, that was removed from the requirements after tests shown , that motorcycles contributed about .001 % of the emissions in Maricopa county the county that the Phoenix metro is located in .

CARB ( California Air Resources Board ), the state entity in California that has the say in environmental issues didn't mandate that motorcycles be emission tested .   
They were the strictest in the US for vehicle emissions .

I believe that after around late 1974, early 1975 leaded fuel was not available to most people in the US, only rural farming areas still has access to leaded fuel for farm equipment .

[DeeG]

I believe that after around late 1974, early 1975 leaded fuel was not available to most people in the US, only rural farming areas still has access to leaded fuel for farm equipment .

I wonder if the 100LL I put in my plane would make my airheads run better. I know the Jet A sumped from the Lears made my VW Rabbit feel special. 

What irritates me is many years ago, we spent a small fortune doing an auto gas STC on our Stinson. Except that with all the ethanol in car gas in the last few years, we can't use it. Have to find non ethanol fuel. Its cheaper than avgas, but a PITA to find.   :-/

[Tony Smith]

Starting with the 1973 model year vehicles made in the US, unleaded fuel has been mandated, the fuel filler, had a reduced diameter hole, so regular leaded fuel could not be used .

Bob - I apologize.

In Australia unleaded fuel did not become mandatory until 1 Jul 1985. Leaded fuel remained available until the late 90s and new vehicles had a smaller fuel filler that prevented leaded fuel being used.

I assumed that for once Australia was not ten years behind - I was wrong.