Loss of compression

[mkj]

I have been having trouble starting my r80/7, nor will it idle on the right side. I eliminated the carbs by swapping right to left, turns out the tappets had closed up on the right side causing a loss of compression, the left side is good 150 psi with a flat zero on the right. I am naturally concerned about this, loosening of the valve adjusters has restored the compression . Should I now run it and keep an eye on the tappets or should I take the head off ?

[Kurt in S.A.]

If it were me, I'd recheck my procedure for valve clearance setting just to be sure. Pretty unusual for one side to be fine and the other side be way off. Recall that valves are set at TDC on the compression stroke. Once you do one side, the engine must be rotated 360 degrees to set the other side. Set the valves right and ride the bike 50-100 miles and recheck.

Kurt

[Rob Frankham]

Be very aware of Valve seat recession (VSR). There have been an awful lot of things said about this and it isn't worth going into them all but from my reading...

1) VSR exists... there are far to many established cases to say that it is a myth

2) It is almost completely unpredictable. The occurence appears to depend on the components involved, the previous use of the machine, the way the engine is used and a number of other considerations. It isn't inconceivable that it would affect one cylinder more than the other.

3) While it generally affects exhaust valves more than inlet valves but can affect both.

4) The general initial signs are valve clearances closing up in use. If they have closed so much that compression is affected, then it is possible that the recession is very rapid and needs to be addressed quickly... this, of course, depends on how long it has been since the clearances were last checked and how many miles the bike has done.

I don't know whether VSR is the (or a) problem in this case but, if the symptom is not associated with any work done to the machine... which is to say that it has occured in general use and the bike has been running well before that... then it seems clear that something has happened to cause a large change in the clearances.

I would be inclined to lift the head, remove the valves and check the valve seats as a matter of course before running the bike. At least keep a very strict check on valve clearances for a while.

Finally, ot would be a good idea to check the tightness of the cylinder studs. If they have loosened off, it will cause the valve clearances to close up.

Rob

[Kurt in S.A.]

How many miles on the engine?

Kurt

[melville]

Yeah, I'm with Kurt--if both valves were tight and the other side was good, it could have been a maladjustment.

My /6 had both exhaust valves receding at about the same rate a few years ago, to the point that they'd both lose the .008" clearance in a few hundred miles.

[jackonz]

VSR, this has been an issue with older ICE engines since the removal of lead in petrol, back in the late 1970s it was removed from petrol here in NZ and the result was high wear in valves (exhaust) and valve seats if the head was cast iron it kept us real busy re machining heads and installing Duraloy valve seat inserts and Stellite valves.
Engines from Japan did not suffer in general from this problem apart from the odd very early models that were a copy of the old BMC engines, what did were all the pure cast iron heads from USA and Australia.
There was a kit you could purchase that would add an upper cylinder lubricant to the intake and was claimed to cure the problem.
VSR was also bad on engines that were converted to LPG.

The lead in the petrol had a 2 benefits, first it reduced the detonation issue on high compression engines and second helped lubricate the valve seats and guides.

I would do what Rob suggested and remove the head and check the valves.

[mkj]

Thanks you all for your concern and informative response, I have suffered VSR in the past when decide to run my 1200 VW beetle on lead free fuel, it lasted 20,000 miles but then it dropped a valve on the motorway, the valve head went through the piston crown and wrecked the inside of the engine. I last retorqued the cylinders heads around 5,000 miles ago absolutely certain I checked the clearances then. I also switched from E5 fuel to E10 mostly bought at supermarket filling stations around the same time, I have noticed a gradual increase in fuel consumption over the same period which is worrying. I intend to use a tank of fuel and then check the clearances and just hope it was my cackhandedness .
Manged 40 miles today seemed to go really well but at only 3 c and a bit wet that was enough. Bought some haddock and went home, they had whole mackerel today as well .

[Rob Frankham]

I've seen no suggestion that the quantity of ethanol in fuel has any relevance for VSR. Other problems but not that one. The issue revolves around the lack of tetraethyl lead in petrol and this has been the case for over 20 years (in the UK). There are various ways to tackle it, which I'm sure you're aware of given your experiences, but the thing about this occurence is that appears to have happened very quickly (whether it be VSR or anything else) and I would suggest that you need to get to the bottom of it without delay or risk... well you know the risks...

Rob

[jackonz]

Thanks you all for your concern and informative response, I have suffered VSR in the past when decide to run my 1200 VW beetle on lead free fuel, it lasted 20,000 miles but then it dropped a valve on the motorway, the valve head went through the piston crown and wrecked the inside of the engine. I last retorqued the cylinders heads around 5,000 miles ago absolutely certain I checked the clearances then. I also switched from E5 fuel to E10 mostly bought at supermarket filling stations around the same time, I have noticed a gradual increase in fuel consumption over the same period which is worrying. I intend to use a tank of fuel and then check the clearances and just hope it was my cackhandedness .
Manged 40 miles today seemed to go really well but at only 3 c and a bit wet that was enough. Bought some haddock and went home, they had whole mackerel today as well .

Oh they were a known issue on the old VW beatle motors, when we stripped them down if you took an exhaust valve and held it by the stem and tapped the valve head on a vice 90% of the time it would break at the neck, so we always replaced all of the valves.

[mkj]

So far I have covered 100 miles despite the cold weather, checked the clearances today and no change also checked heads bolts which are also good. Will keep an eye on ( ear really ), a change in engine note will give it away. If the valves are rattling the engine is running.