compression

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el rojo
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compression

#1

Post by el rojo » Sat Apr 04, 2015 4:51 am

I did a top end job and am putting her back together. Intake manifold installed and leak tested, carb and support bracket on and then I decided to do a compression test. I did the back first and got it up to 110 lbs. I then did the front and only got 55 lbs so I went back and re did the back jug and now only getting 65 lbs no matter how long or hard I kick! WTF? I have only had the bike about 2 years and have never done a compression test til now.
I have no clue as to what a standard 62 pan should be running but 55 and 65 lbs to me sounds low? I don't want to go any further putting her back together until I find out weather I need to pull the heads again and jugs and see what the hell is going on. I bought the bike from a guy in California sight unseen except pictures. I called some dealerships around the area and they refured me to a guy who specializes in the older bikes and told him I would pay him to go check it out before I shipped it to Hawaii.
Ride it around the block and check the compression etc. For some unknown reason and it could just be me, he resisted on checking the compression and just said that he would be able to tell by how it started and kicking it. Any feed back on that? I belong to a club on the Big Island and we are sponsering a polker run next weekend and I would really love to take the bike but not if I shouldn't be riding her with the compression I have.
Rojo



58flh
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Re: compression

#2

Post by 58flh » Sat Apr 04, 2015 11:43 am

Elroho---You should of had the carb.-support ON when Pressure testing the intake!-Then when you put ths carb. on BE-CAREFUL not to move it up/down /sideways>>>.You could have made a intake leak when you mounted the carb.!--Try putting some oil in the front cyl.& open the throttle wide & do compression test!-(Also rub a finger /If you got gas in it & makesure the clamps are DRY on the bottom.Another reason could be a valve to tight in front jug.On a fresh motor you should be within 10-15lbs. of eachother!.If it hasent run yet /Then that's good!--I would pressure test the manifold/you may be surprised!.First do the easier part & check your valve adj. If its good & both valves can shut/You have a Manifold leak.As I said before I pressure test once evey month or 6-weeks.As soon as I get a little fuel on my finger ,I know its Tighten clamp time!-How much??Until there are no bubbles.---Respectfully---Richie---Also it is not uncommon to have different compression numbers on a top end that didn't run & have a chance for the rings to seat.--I personaly think if you have no leaks with the intake/Your comp. is right where it should be dry.Again if adding some oil thru the plug hole & it rises some (Do not have to be the same!-You already got over a 100lbs. on the rear.Remember tape the throttle WFO.add a oz. to each jug & kick her over a few times without the plugs in (5/6-times to distribute the oil .Now take your readings.They will come-up.As long as NO -INTAKE LEAKS! Start that bike & if you got brakes & everything is hooked-up/sounds like it is GO for a ride-Remember a fresh top-end will get hot faster.Thats ok!-Just vary your RPMs & don't go over 55mph until you have 300-miles or more!-Your rings will have found a home & the Pistons are getting there.Do 5-6 oil-changes in the first 1200-miles.Now ENJOY the fruits of your labor & put some rubber to the road!--Best of luck---RICHIE

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Re: compression

#3

Post by kitabel » Sat Apr 04, 2015 2:06 pm

It has nothing to do with intake leaks. The carburetor can be completely removed for a compression test.

58flh
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Re: compression

#4

Post by 58flh » Sat Apr 04, 2015 2:55 pm

Ofcourse it can!--But if is already bolted-up--The smart thing is to open the fly,Pour some oil & do your comp. test!---Also the carb. need not be on when nlooking for leaks!--As long as he had the intake lined-up WITH the support-Then what the hell is the carb. needed for?--The man said He did a pressure leak test without the support.I merely said If you move that intake around it will make a leak.--Richie

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Re: compression

#5

Post by Tattoo » Sat Apr 04, 2015 2:57 pm

kitabel wrote:It has nothing to do with intake leaks. The carburetor can be completely removed for a compression test.

Yep that's right..........

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Re: compression

#6

Post by Bigincher » Sat Apr 04, 2015 4:06 pm

58flh wrote:.........The man said He did a pressure leak test without the support.....Richie
At first when I read his post, it looked to me like he was saying he did the leak test with the carb and bracket installed, but when I read it again, maybe not.

Mark44
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Re: compression

#7

Post by Mark44 » Sat Apr 04, 2015 5:40 pm

El rojo,
Did you do the first compression test, then ride the bike a bit, and then do another compression test? After the engine is run for the first few times, you need to go back and retorque the head fasteners and cylinder nuts. Also, until the rings seat, you're not going to get very high compression values. How long they take to seat depends on the kind of rings you used, as well as the kind of oil you're using. Chrome rings take long to seat, and synthetic oil is so slippery, you dont' get the friction needed to let the rings wear enough to make a good seal.

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Re: compression

#8

Post by el rojo » Sat Apr 04, 2015 6:52 pm

Sorry for being confusing but it sounds like I was by the responses I got.
When I said I did the top end, I meant that I had a machine shop check the valve guides, lap the valves, replace one exhaust valve and check the rocker arms and glass bead the heads. I didn't remove the jugs so the rings are seated I would assume from many miles of riding already.
When I went back and went threw all the parts, I noticed that my manifold and carb never had a support bracket to start with so I fabricated one just because it made sense from what I have learned on this forum. The only place I could see to attach the support on the carb was the brass hex headed drain plug on the bottom of the float bowl which has an O ring seal which meant that my support would have to have a hole in it that the brass nut fit threw and if the support was not exactually flush with the bottom of the bowl, I felt that there would be a leak so I opted to do the next best thing and made it so that the carb just bearly rested on the support so that it could never go down if I hit a bump.
As I said, it never did have a bracket before and seemed to work.
As far as the compression test, I can't see why having the intake manifold on or off would make any difference at all because the valves are closed (hopfully) when the piston is comming up so why would the manifold have anything to do with it? I didn't ride the bike between first checking the back jug and got 115 lbs and then checking for front one and getting 55. I am still perplexed as to why I would of gotten 115 at first try and then 65 lbs there after??? Still would like to know what should I expect for an average compression for that year (62) and no modifications??
Rojo

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Re: compression

#9

Post by Bigincher » Sun Apr 05, 2015 1:12 am

I wouldn't even worry about the compression right now. Got to ask what prompted you to do a valve job, though. Was it smoking a lot? Loss of power?
Colony has good repro support brackets (I think). If it was me, I would assure the manifold is leak-free, install the correct support bracket, button it up and ride it. If everything is dialed in and it runs good, then I would check the compression, just out of curiosity. Your first number of 115 psi would seem reasonable. Whatever the readings are, the two cylinders should read within 10% of each other. I have no explanation for the first reading of 115 followed by subsequent readings of 85, unless one of the valves got stuck a little bit.

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Re: compression

#10

Post by el rojo » Sun Apr 05, 2015 6:47 pm

Bigincher wrote:I wouldn't even worry about the compression right now. Got to ask what prompted you to do a valve job, though. Was it smoking a lot? Loss of power?
Colony has good repro support brackets (I think). If it was me, I would assure the manifold is leak-free, install the correct support bracket, button it up and ride it. If everything is dialed in and it runs good, then I would check the compression, just out of curiosity. Your first number of 115 psi would seem reasonable. Whatever the readings are, the two cylinders should read within 10% of each other. I have no explanation for the first reading of 115 followed by subsequent readings of 85, unless one of the valves got stuck a little bit.
This may sound crazy but the only reason I pulled the heads was to replace the rocker arm covers with new chrome ones and have the heads glass beaded. I figured it would also be a good time to have a look at the valves and have them replaced if needed or re seated as anything I can do to raise the compression is a plus since it's not an electric start. I went back since my last post and re checked the compression and got different values every time I did it until I came up with 95 lbs front and back so I quit while I was ahead! Still like to know what the average compression should be expected though.
Rojo

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Re: compression

#11

Post by Panacea » Mon Apr 06, 2015 1:44 am

95 sound real good to me.

el rojo
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Re: compression

#12

Post by el rojo » Mon Apr 06, 2015 3:07 am

Panacea wrote:95 sound real good to me.
I agree, I'd be tickeled pink if it were true but unfortunately almost every time I took it, I got a different reading so I will have it checked later professionally as my gauge may be crap!
Rojo

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Re: compression

#13

Post by Bigincher » Mon Apr 06, 2015 4:01 am

Don't lose any sleep over it, Rojo. Just ride it. If the compression is lousy, you'll pick up on the tell-tale signs. Or maybe you'll be having so much fun, you won't even know it. You can't hurt anything with low compression, no worries.

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Re: compression

#14

Post by Tattoo » Mon Apr 06, 2015 4:22 am

I guess I should ask... What kind of a cam do you have? Does it have a lot of duration?

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Re: compression

#15

Post by 58flh » Mon Apr 06, 2015 1:22 pm

Tattoo wrote:I guess I should ask... What kind of a cam do you have? Does it have a lot of duration?
Tatoo--Sounds like a stock fl cam.-As He said it kicks over easily enuff!--A FLH cam he would notice that he has to put some ass on the pedal to roll-her over./Could be a #1 or J cam to.There easily started by hand if you had to!---At any rate lets see what he says hes got.Because we can guess all day :lol: !-----Respectfully---Richie

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