'95 R100GS. To be done with a warm engine and carbs off?
What sort of reading should I expect?
Its done 65k miles and no overhaul.
TIA
What sort of reading should I expect?
Its done 65k miles and no overhaul.
TIA
Compression testing.
- Thread starter Redboots
- Start date
8.5-10.0 Bar apparently.
Info is from my Haynes manual. Over 10 good, 8.5-10 normal, below 8.5 poor.
And of course should both be the same
And of course should both be the same
Did you try it again with a squirt of oil in the bores?
No. Wont that give a false reading?
It will indicate if it's the valves or bores that are leaking.
This place is a mine of information 
By remaining the same if its the valves and increasing if its the rings?
yes. the oil will seal the rings/bore to some extent.
i would have explained better, but i was on my phone
B Murr
Registered user
If putting oil in the bores, as they are lying on their side I'd guess that it will just seal the lower parts of the bores. I guess that if you squirt it in using an aerosol can it will be a bit more widely spread and more likely to seal most of the circumference of the rings.
Result is 9 bar on both sides. Looks like winter job.
Can you hone these bores? Scotchbright pads or sumat
Can you hone these bores? Scotchbright pads or sumat
solidstate100
Registered user
Result is 9 bar on both sides. Looks like winter job.
Can you hone these bores? Scotchbright pads or sumat
With that result I wouldn't be so sure its the bores that need re honing. As there has been only a small increase in the compression pressure (even a very good ring/bore seal will improve a small amount with an oil "sealant") it may actually indicate that its the valves that are actually leaking. A better additional diagnostic solution would be to carry out a cylinder leak down test (i.e. in a nutshell charge the cylinder with compressed air and monitor any decrease in pressure whilst listing at the inlet/exhaust port).
As pet of the diagnostic procedure I would also be paying attention to oil consumption, and what evidence of smoke there is - all the time, on overrun only, only after starting the engine from cold etc.
What sore of mileage has the engine done? -the Nikasil coated bore of the Boxer engine can potentially rack huuuge mileages with virtually no signs of wear whereas the valves not so much.
my guess is that at 65K, the heads need an overhaul. so considering the not unknown phenomena of exhaust valves falling apart in those engines at that sort of mileage, it might be worthwhile whipping the heads off at a convenient time ("Winter is coming") and have a look.
Err, I'd expect them to be Nicasil plated so honing etc is a no no.
If the Nicasil is worn out our damaged, you'll need to get it properly re-plated.
If the plating isn't damaged (you should be able to visually inspect them with the heads off) then simply replacing the rings might improve things, but as the compression is comfortably in the normal range, I'd be tempted to leave well alone.
If the Nicasil is worn out our damaged, you'll need to get it properly re-plated.
If the plating isn't damaged (you should be able to visually inspect them with the heads off) then simply replacing the rings might improve things, but as the compression is comfortably in the normal range, I'd be tempted to leave well alone.
That is my plan
Poor choice of word ref the honing. More a de-glazing is what I had in mind.
I've had this bike for 7 years now and I think I'm going to move it on.
I may not though and a bit of fettling wont go amiss either way.
It also needs a good clean of all things aluminium. Where I lived before, salted roads are unheard of. Alas, oop north the Frenchies and the Germans use lots of it
Beemerboff
Registered user
And when the heads are off you may as well do the rings as well--------.
Brown Aluminium Oxide Scotchbrite, from a painters store, will clean up the bores a little and help the rings to bed in.
Brown Aluminium Oxide Scotchbrite, from a painters store, will clean up the bores a little and help the rings to bed in.
Is that really a good idea on Nicasil plated bores?
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