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A65 low compression #738004
06/07/18 11:05 pm
06/07/18 11:05 pm
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
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GeauxTwins  Offline OP
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G

Joined: May 2018
Posts: 17
Louisiana
Bikes is getting more difficult to start. Used to go 1st kick.
Now, I have to kick prime 2 to 3 times when cold.
Absolutely no problem bump starting.

Checked electrical, charging, coils, battery, new spark plugs (B7ES), voltage regulator, timing strobe.........but the Boyer
Opened / cleaned carb

So compression test dry and with an oil squirt:

Engine hot and new pressure gauge tool

Right dry = 105 psig
Right oil = 115 psig
Delta Right = 10 psig (10%)

Left dry = 190 psig (pretty high but no clue what kind of piston / ratio I have)
Left oil = 210 psig
Delta Left = 20 psig (10%)

Obviously, I have an issue with the R cylinder

With only 10% difference between dry and oil psig reading, can I conclude this is not a piston ring issue?

Thanks


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72
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Re: A65 low compression [Re: GeauxTwins] #738008
06/07/18 11:19 pm
06/07/18 11:19 pm
Joined: Nov 2011
Posts: 189
Nova Scotia, Canada
K
koncretekid Offline
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koncretekid  Offline
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K

Joined: Nov 2011
Posts: 189
Nova Scotia, Canada
Buy or borrow a "leak down" tester which screws into your respective spark plug hole and pressurizes the combustion chamber at top dead center (actually just past TDC) on the compression stroke (requires an air compressor). Restrict the crank from rotating by a breaker bar on the crank nut or even by putting the bike in 1st gear and havlng someone hold the rear brake on. The leakage will be apparent from the exhaust pipe, the intake, or the crankcase breather, indicating which is the culprit. It won't solve the problem, but will eliminate rings if no leakage thru the breather, and will point out if one or the other, or both valves are defective.
Tom


Life's uncertain - go fast now!
Re: A65 low compression [Re: GeauxTwins] #738012
06/07/18 11:59 pm
06/07/18 11:59 pm
Joined: Aug 2005
Posts: 1,500
melbourne florida
B
bodine031 Online content
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bodine031  Online Content
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Joined: Aug 2005
Posts: 1,500
melbourne florida
As koncretekid says. A leakdown tester to get a real result, otherwise you are guessing and wasting time.

Re: A65 low compression [Re: bodine031] #738015
06/08/18 12:51 am
06/08/18 12:51 am
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
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GeauxTwins  Offline OP
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Joined: May 2018
Posts: 17
Louisiana
Thanks guys,
I'll get a leak tester from my local garage,
Yes, better spending all the time needed on a diagnostic to get to the root cause than dismantling everything like going fishing
I'll follow up with my findings


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72
Re: A65 low compression [Re: GeauxTwins] #738049
06/08/18 1:07 pm
06/08/18 1:07 pm
Joined: May 2004
Posts: 3,862
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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B

Joined: May 2004
Posts: 3,862
Sydney Australia
And because you can never have too many toys, get your hands on a bore-a-scope.
You can get quite good ones that are USB powered off your laptop.
Stick it in the plughole and have a look.
Shine a strong light down the carb throat and look for light inside the cylinder.
You can do the same with the exhaust if the pipes are off .


Bike Beesa
Trevor
Re: A65 low compression [Re: GeauxTwins] #738052
06/08/18 1:22 pm
06/08/18 1:22 pm
Joined: Dec 2013
Posts: 4,429
ohio, usa
kevin roberts Online content

DOPE
kevin roberts  Online Content

DOPE

Joined: Dec 2013
Posts: 4,429
ohio, usa
damn.

walmart sells boroscopes for ten bucks that connect to your telephone.


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: A65 low compression [Re: GeauxTwins] #738104
06/09/18 12:24 am
06/09/18 12:24 am
Joined: Mar 2006
Posts: 1,358
Magnolia, TX
htown Offline
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htown  Offline
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Joined: Mar 2006
Posts: 1,358
Magnolia, TX
My poor boy method. Pull the head. Whether it is rings or valves you are going to have to do this anyway to fix it. Dump some gas in each of the combustion chambers on the head. Look for leakage. If there is no leakage it is almost certain the rings are the problem.
I have a leakdown tester but I hardly ever use it. It's very hard to lock the crankshaft. If you lock the rear wheel the slack in the primary and drive chain still allow too much movement. Only way is to get a wrench on crank nut but then you have to pull the primary cover off and have a buddy hold the wrench and hope you don't loosen the nut in process.

Last edited by htown; 06/09/18 12:39 am.

1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
Re: A65 low compression [Re: kevin roberts] #738302
06/10/18 10:40 pm
06/10/18 10:40 pm
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
BritBike Forum member
GeauxTwins  Offline OP
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G

Joined: May 2018
Posts: 17
Louisiana
Yes, looking at a cheap borescope too,

The Walmart and other cheaper ones have a small camera diameter (7mm or less) but the hard tip looks like 2" long so okay for viewing the pistons but I doubt it is short enough to be orientated toward the valves.


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72
Re: A65 low compression [Re: GeauxTwins] #738320
06/11/18 3:15 am
06/11/18 3:15 am
Joined: Mar 2006
Posts: 1,358
Magnolia, TX
htown Offline
BritBike Forum member
htown  Offline
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Joined: Mar 2006
Posts: 1,358
Magnolia, TX
Checked valve clearances?
You have proved you have low compression in one cylinder. Maybe the leak down would tell you whether it is valves or rings. But there are other ways to do that. What do you hope to see with a borescope or leakdown tester where the next step is not taking the head off?
Bore or piston damage or worn bores
valve damage
blown head gasket
everything looks okay but the compression on one side is still low



Last edited by htown; 06/11/18 3:19 am.

1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
Re: A65 low compression [Re: kevin roberts] #738322
06/11/18 4:40 am
06/11/18 4:40 am
Joined: May 2004
Posts: 3,862
Sydney Australia
B
BSA_WM20 Offline
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BSA_WM20  Offline
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B

Joined: May 2004
Posts: 3,862
Sydney Australia
Originally Posted by kevin roberts
damn.

walmart sells boroscopes for ten bucks that connect to your telephone.


That would be for hipsters to take selfies of their tonsils wouldn't it.


Bike Beesa
Trevor
Re: A65 low compression [Re: GeauxTwins] #738332
06/11/18 6:24 am
06/11/18 6:24 am
Joined: Aug 2001
Posts: 134
Anchorage Alaska USA
M
Mitch Offline
BritBike Forum member
Mitch  Offline
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M

Joined: Aug 2001
Posts: 134
Anchorage Alaska USA
ha ha... either that or the no man's land below yer scrotum patch. anyway, I don't think its compression

Re: A65 low compression [Re: GeauxTwins] #739077
06/18/18 12:51 pm
06/18/18 12:51 pm
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
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GeauxTwins  Offline OP
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G

Joined: May 2018
Posts: 17
Louisiana
Well, I found the problem,

Bike has been hard to kick-start since I replaced the 4 tappet adjusters but I didn't connect the two since I knew my valve gaps were set correctly.

The rocker head cover was on when I did the compression tests,

After replacing the exhaust pushrods (see other post), I did a cold compression test with not head cover on and got over 170 psig for both cylinder,
I was puzzled! Put a new gasket, bolted the head cover on then another cold compression test. Left a 170 psig and right at 100 psig! Dang it!

Took cover out, checked it inside and noticed two marks by the inlet side with a deeper groove for the right side. Conclusion: tappet adjusters were hitting the cover so inlet valves couldn't close properly so low compression.....

Took out the 2 new inlet adjusters and compared to the old ones: longer by 2 mm (27 mm versus 25 mm for the old ones)!!
Put back the old adjusters for the inlet valves, bolted head cover then compression test: both cylinders > 170 psig!

New adjusters are Allen type head and sold as replacement part 68-0155

My questions to the experts:
1 - Can I polish the old adjuster tips and re-use?
2 - Can I shorten the new ones by 2 mm?

There is definitely too much kinetic meat over the securing nuts (6 to 8 mm of free threads!)


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72
Re: A65 low compression [Re: GeauxTwins] #739112
06/18/18 5:32 pm
06/18/18 5:32 pm
Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
gavin eisler Online content
BritBike Forum member
gavin eisler  Online Content
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Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
yes to both, I would grind 2 mm off the top of the new ones, as long as the allen key still engages that would be for the best i reckon. Check how deep the allen key socket is first. no point in wrecking them completely, are the new type the mushroom head sort?


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A65 low compression [Re: gavin eisler] #739120
06/18/18 6:15 pm
06/18/18 6:15 pm
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
BritBike Forum member
GeauxTwins  Offline OP
BritBike Forum member
G

Joined: May 2018
Posts: 17
Louisiana
Thanks Gavin,

Allen key goes 1/4" in so I can cut at least 2 mm
Could cut more and shave the upper end so to fit a 1/4 spanner for adjusting as original ones

Not mushroom heads


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72
Re: A65 low compression [Re: GeauxTwins] #739163
06/19/18 11:22 am
06/19/18 11:22 am
Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
gavin eisler Online content
BritBike Forum member
gavin eisler  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 4,114
argyll. scotland, uk
If the new ones are longer than the originals, trim to equal, then square or slot the end if you need to , you dont want extra weight out there. If the old ones also have a lot of thread spare at the top, it suggests the valves are too long ( unlikely) or that the seats are pocketed ( quite likely). Nothing short of valve seat replacement will change that.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: A65 low compression [Re: GeauxTwins] #739171
06/19/18 1:49 pm
06/19/18 1:49 pm
Joined: Feb 2007
Posts: 645
Ewing. NJ
E
edunham Offline
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edunham  Offline
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E

Joined: Feb 2007
Posts: 645
Ewing. NJ
My Trident had a similar issue. The tops of the valve adjusters were hitting the valve covers. The cause was pocketed valves. I used oversize valves to get the geometry back where it ought to be. Worked fine for a few years. I then replaced the head for unrelated reasons.

Ed from NJ

Re: A65 low compression [Re: GeauxTwins] #739261
06/20/18 11:38 am
06/20/18 11:38 am
Joined: May 2018
Posts: 17
Louisiana
G
GeauxTwins Offline OP
BritBike Forum member
GeauxTwins  Offline OP
BritBike Forum member
G

Joined: May 2018
Posts: 17
Louisiana
Old adjusters protrude by 6 to 7 mm over the securing nut. Can take 2 mm out.
New ones by 8 to 9 mm
Will trim the latest by 2 to 4 mm

Will check for valve pocketing when taking head out for replacing my slightly leaking cylinder bottom gasket

Thanks


Trophy 67, A65T 70, T100C 70, TR6R 71, Daytona 72

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