Dear All,
After sort distance test (when to office around 70 mil for several days) I continue to test with long distance around 100 mil for 6 hours with 1 hours break time (twice) my M20 got lost compression a lot (estimated remaining pressure 10%). I suspected on tapped setting was change then I tried to re set the clearance inlet and out let tapped gap. I changed several times till got the problem on tapped lock nut (broken to two pieces). Now I have to get the lock nut and find out the problem. I have removed the boring and there is the small scratch at boring surface. It looks I have to do oversize the boring and change the piston ring. The next is check the clearance of the valve inlet and out let. Questions are:
Is my thought correct ? Any other things need to be check ?
During the test oil level was too low (not at the middle of the level oil tank). Is this condition the root cause ? Because scratch shown at the boring surface. Or because the oil pump performance is low. When I checked the oil flow from the oil tank cap, oil flowing slow during stationer and oil sprayed when I increase the throttle.
Please help. Appreciate for all of you comment and advise.
Regards
Rofiq
email (option): rofiqmgl@yahoo.com
Hello Rofiq,
If you have a tappet that is not correctly adjusted it will give you trouble! Replacing that broken nut would be the first thing to do. Make sure you have plenty of oil. And if the scratch on the bore is small (as you say) perhaps it doesn't require a rebore.
Rather than do everything at once try fixing the obvious thing first -- that would be the tappet nut. Then check the valve seats for wear. A prime source of decompression is worn valves and seats, followed by a blown head gasket.
I hope this helps.
Allan
email (option): allanmatchless@yahoo.com
Also check your exhaust valve lifter is not fouling the tappet and when everything gets hot and expands it stops the valve from closing fully. I also had a problem on a previous m20, back in my youth, with a manufacturing fault on the exhaust tappet. The hole on the tappet had not been cut deep enough or possibly not threaded to the full depth, but the end result was the tappet bottomed on the follower before you could achieve the correct gap - you could not get any clearance! This caused the top of the follower to shear off. It was only then that I discovered the problem! Back in those days it was easy enough to get a new follower over the counter locally, and my 'fix' was to file some of the end off so that the tappet could come lower. No, I would not do that these days :-) Reading your issue I wonder if you may have experienced something similar? Dunc
Hi Allan and Dunc
Many thanks for your advise.
Agreed to solve the tapped nut problem first. Now the tapped nut is on the way to my house (has to wait for some time from UK). Next time I have to maintain the oil level at normal level. Hope the scratch is not affect on compression.
I will check the valve, seat and may replace the gasket.
Confirm that the valve lifter is not touch the top of exhaust tapped.
Hi Dunc
Could you please explain more detail for "follower" ? At my tapped surface inlet and out let are not flat. I got difficulty to measure the tapped clearance. Is your problem same with me ?
Regards
Rofiq
email (option): rofiqmgl@yahoo.com
Rofiq
Email sent as that is easier than posting photos on here. :-) Duncan
Hi Rofiq
if you adjust your valve clearance, make sure you do that exactly by the book. Thats the only right way to do it.
Last year my M20 was losing compression because the ignition timing had changed over the years (they sometimes do). I had only 6 mm pre ignition left.
After re-adjusting tot 11 mm pre ignition the problem was over.
Hi Duncan
Many thanks for your help. I your explanation is very clear and I am very happy knowing that case.
Hi Michael
Sure I am follow the instruction manual to set the tapped gap. Regarding the ignition timing now I set at 5.5 mm but it is not a problem at my bike because before I got this problem the compression was very good. I have to release the compression with valve lifter before I kick start but now a almost no need the power to kick it. Let me try to set at 11 mm as well once install new tapped nut (still waiting that nut).
Regards
Rofiq
email (option): rofiqmgl@yahoo.com
Hi Rofig
I just completely burned a gap through a composite head gasket. I lost so much compression that I thought I had burnt out a valve or burnt through a piston.
I could hear a head gasket problem, but the bike just didn't get me home before compression completely gave out. I had to push it 1/2 a mile along a green lane.
One to check too!
Regards
Pat
email (option): sacombsashtrees@hotmail.com
Hi Pat
Many thanks for your reminder. I have checked the gasket and it is very tight and not possible to get leak there. Now the bolt is next problem for me. Very difficult to loose the bolt. Still thinking how to do.
Regards
Rofiq
email (option): rofiqmgl@yahoo.com