B16 compression test

[arcturus]

Did a comp' test yesterday and the results showed 1-2 &3 cylinder about 9 bar. Number four showed 4 bar! I want to do oil test to determine valve or ring. Can someone please clarify this test for me. My understanding is that you put a small amount of oil down plug hole and re do test. If pressure jumps up then it's a ring.

Weird, I retested this morning before doing oil test and all pressures were equal! 9 bar. Perhaps I hadn't screwed the gauge in properly. Will retest again later just to be sure.

[Derek UK]

Carbs at full throttle during test? Nothing to stop you putting a little oil down the plug holes and doing the tests again. The difference in numbers between the dry and wet tests might prove enlightening.
My first Amazon back in 1966 had a B16. It went well but burnt oil. Pulling the pistons found broken rings on 3 of the 4 pistons. Rebored etc and that cured the oil burning but didn't noticeably improve the performance. 80 cruise, no OD, was easy! Things were different back then...……..

[arcturus]

Re tested. Before oil number 4 - 3 - 2 - 1 cylinders
9.5- 8 - 10 - 10 bar
with oil 11 - 9 - 10 - 10 bar

Would I be correct in suspecting valves?

[Derek UK]

Certainly #4 is a bit suspicious. It did improve after the oil was added so that would indicate a ring problem. Broken rings can scratch the bore and that can also reduce compression. Oil doesn't normally improve leakage from a burnt or chipped valve. Have you checked the valve clearances? Have you ever had the head off the engine?

[arcturus]

Valve clearance good. I intend now to lift head and at the same time have hardened seats fitted and probably any other work done.Had head off just after I bought car five years ago. Will check bores at same time. Hope it's not a ring and engine out again. Only just completed that job (gearbox)in July. At least it' the right time of year, no more rallies etc till next Spring

[mocambique-amazone]

Hello George.
Do a pressure lost test.
This will show clearly where the ( a) problem is/will be.
If the pistons and rings are good:
Cam lift
Bad ports
Sticked carb/ pistons inside carbs maybe a problem too.
A compression test is good enough to present the condition of the engine. Does explain nothing for bad luck.
I only trust one result: all cylinders even in bar/psi

You will find the tool at the bay, maybe one of your friends in Portugal will own and share one.
Good luck, Kay

[arcturus]

I have the tool but don't have necessary compressor!

[mocambique-amazone]

Cheapest version:
Find a used pressure tank from a truck, play with some adapters and get the tank filled at a fuel station.
Or ask a diver, the have 10l bottleso filled with 100 bar of air.
A pressure reducer like for a welding machine: done!
Good luck, Kay

[arcturus]

Will probably lift the engine next week. Also have a ticking noise,similar to that which I had on my 144 B20 before the fiber timing gear lost some teeth. Need to check that. Hope it's not gear as undoing the nut really needs an impact gun which I don't have.

[Derek UK]

The fibre gear in the B16 has the fibre attached to the steel centre just by a knurled pattern on the steel. It doesn't have the star pattern steel centre like the B18/20 gear. That means that the B16 gear just parts company with the centre with no warning, One second the engine is running, the next second it isn't. I don't think it's an interference engine. The crank will continue to turn if you are in gear but the cam won't drive the valves or the distributor. I have had this failure. A quick check showed that the distributor wasn't turning when the engine was turned by hand. My failure happened "safely" in town. New gear kit fitted and all was well. Just saying that as there wouldn't be any ticking that would indicate a pending gear failure.