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Author Topic: Minimum compression on a R65 head  (Read 6251 times)

Adamastor

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Minimum compression on a R65 head
« on: October 04, 2009, 04:50:02 PM »
Hi there!

A friend of mine just gave me a compressor tester and I tried it on my R65. Results (with throttle fully open):

LS = 145 psi
RS = 115 psi

That's quite a difference.. i searched the internet but did not find what is the factory standard and what is the minimum acceptable for a R65 head.

Is 115 too low? Is it bad for so much difference between the two cylinders? If I want to get the right side better should I look for new valves or new piston rings?

Cheerio!

Sergio
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Offline Lucky_Lou

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Re: Minimum compression on a R65 head
« Reply #1 on: October 04, 2009, 04:59:57 PM »
115 seems low check the valve clearances on that side before you wade into stripping it, mine is 145 on both sides checked after rebuild including piston rings 600 miles back.
Lou
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Offline Bob_Roller

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Re: Minimum compression on a R65 head
« Reply #2 on: October 04, 2009, 05:15:58 PM »
Straight from the BMW shop manual :  above 142 psi good, 121-142 psi normal, below 121 psi poor .

The right cylinder needs some work .

First off, have you done a valve clearance check/adjustment, if you haven't done that yet, I would check it, you may have too close of a clearance on a valve, and it may not be closing all the way .

If the compression tester has a separate part that threads into the spark plug hole,  has a 'quick disconnect' on it, you can connect a compressed air source to it, and with the valves closed,  put some pressure in the cylinder .

If the piston rings are worn, you should feel air coming out of the oil dipstick hole .

If a valve is the problem, you may need to take the intake tube off, and listen/feel for air coming out of the intake .

The exhaust valve is a bit more involved, you may be able to feel air coming out of the muffler .

But the only real way to know for sure, is to remove the exhaust from the problem cylinder, and check for air leakage then .
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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Adamastor

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Re: Minimum compression on a R65 head
« Reply #3 on: October 04, 2009, 05:35:50 PM »
I actually had just re-checked the valve clearances because I had changed the rocker arm adjuster bolt...

Tommorow I will do the oil and intake checks to try to see If I figure out where's the problem...

This cylinder plug was usually more oily/dark than the other one and the carb mixture screw didn't do much difference. That's consistent with low compression, right?
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Offline Bob_Roller

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Re: Minimum compression on a R65 head
« Reply #4 on: October 04, 2009, 05:45:03 PM »
What year is the bike ?
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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Adamastor

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Re: Minimum compression on a R65 head
« Reply #5 on: October 04, 2009, 06:20:18 PM »
1985
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Adamastor

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Re: Minimum compression on a R65 head
« Reply #6 on: October 05, 2009, 10:52:18 AM »
Ok, I have been working on the bike and done the tests you gave me...

Pressure goes no more than 118 psi without carb. I left the pressure tester some time on the sparkplug hole and there is no slow leak. Pressure was stable.
I opened the oil filler hole and while cranking I felt air being sucked in and sucked out as the cylinder goes in and out, but that should be normal, right?
I managed to take out the exhaust nut, but the down tubes are really hard to disconnect from the muffler and the horizontal tubing...

Should I play a little with the valves clearance in order to see if compression alters? I had done the valve job yesterday with .10 inlet / 0.2 outlet.

Should I buy new rings for this piston? Taking the cylinder out should be not that hard after I manage to remove the exhaust tubes... Messing with new valves should be harder for a non-experienced home mechanic like me...

Meanwhile not everything is bad, I discovered that I still have splines and have cleaned/lubbed them :) (they were clean but very dry)

Sergio
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Offline Bob_Roller

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Re: Minimum compression on a R65 head
« Reply #7 on: October 05, 2009, 10:59:44 AM »
When checking the cylinder for leakage, using compressed air, you don't turn the engine with the starter, you just put air in the cylinder, and then feel, or listen for air coming out of the dipstick hole .

You need both valves in that cylinder closed, so pressure can build up .
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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Adamastor

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Re: Minimum compression on a R65 head
« Reply #8 on: October 05, 2009, 02:08:12 PM »
Hmmm back from the garage once again... I have no chance to put compressed air on the cylinder...

Anyway, before thinking of buying rings and valves I went to the garagem and re-done the valve job:

Now I have 125 psi on the worst cylinder!

I assume since this is acceptable (even thou the other cylinder has more compression) isn't it?

(meanwhile also lubed the rear splines... )
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Offline Bob_Roller

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Re: Minimum compression on a R65 head
« Reply #9 on: October 05, 2009, 02:28:08 PM »
If the engine is running good to you, keep riding it, I would keep a close eye on the oil level to see if you have higher than normal oil consumption .

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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Adamastor

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Re: Minimum compression on a R65 head
« Reply #10 on: October 05, 2009, 02:48:56 PM »
I have only ridden about 1500 km on this bike, and yes there is some oil consumption. I am not sure how much, but a bit more than I thought it would be normal..
I will keep on checking and maybe later this year buy some new rings for this cylinder.
Right now I am waiting for the front disc and the dyna coil for taking her out to the road again...

Apart from the 3 rings I would also need the cylinder to engine gasket and maybe the rocker arm rubbers, right?

Regards and thanks for walking me on this :) This forum rocks! :)

Sergio
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Offline Bob_Roller

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Re: Minimum compression on a R65 head
« Reply #11 on: October 05, 2009, 02:53:13 PM »
There's also an o-ring on the cylinder base, and two small o-rings that go on the cylinder hold down studs .

Oil supply for the rocker arms come up around the studs into the cylinder head .

Also be sure to use a head gasket sealant of some sort in the area of the studs, if you don't, most likely you'll develop a leak here .
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'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Offline Lucky_Lou

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Re: Minimum compression on a R65 head
« Reply #12 on: October 06, 2009, 04:46:18 PM »
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bruce_launceston

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Re: Minimum compression on a R65 head
« Reply #13 on: October 06, 2009, 05:50:49 PM »
The other way to see if it is the rings leaking or the valves leaking is to put a small amount of engine oil down the sparkplug hole before doing the compression test.
If it is the rings that are worn, this should raise the compression, if it is a valve problem the compression will read the same as it was without the oil.
I'm not sure how well this works on a horizontally opposed engine, maybe you will have to lay the bike over to get the oil to run around and seal the rings before standing it up for the compression test?

If it was my bike I would budget on replacing the rings on both sides, even though you have good compression on one side. Just doesn't seem right to only do one side.

Cheers
« Last Edit: October 06, 2009, 08:50:22 PM by bruce_launceston »
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Offline nhmaf

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Re: Minimum compression on a R65 head
« Reply #14 on: October 06, 2009, 07:52:25 PM »
125 is within acceptable range, though I would think that if one cylinder has 20 PSI better compression readings it is still going to be doing a bit more work, and the engine won't be quite as smooth as it could be.

So what did you set the valve lash clearance to be on the low cylinder to bring up the number?

I'd ride it as others have suggested, and keep an eye out for oil consumption.   Over the winter when we cannot ride over here, I'd plan to do the rings, and check over the valve seats on both sides, too - if the heads are coming off, may as well get the valves done IF they are in need of it.
« Last Edit: October 06, 2009, 07:53:25 PM by nhmaf »
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