Peugeot 103 LVS-U3 Low compression.

rob res /

Oct 10, 2020 03:59PM

Hi all,

I have a 77 Peugeot 103 and i am having a problem with the compression.

I bought the tecnix stock cylinder kit from treat and installed it and the compression did not improve i am only getting 60 psi same psi i was getting with my old cylinder set up. Currently i have the motor on my work bench that is when i did the compression test after installing the new cylinder, piston and rings

I tested the decompressor valve and it is ok, no leaks i also remove the intake reed valve and inspected it and it is also in good shape.

What should the compression be on a new cyl kit? 60psi seems kinda low?

Any help is appreciated.

Thank you

Re: Peugeot 103 LVS-U3 Low compression.

pat splat /

ggspeed

Oct 10, 2020 08:57PM

lap your old head n new cylinder so its flat or maybe your compression tester is no good.

Re: Peugeot 103 LVS-U3 Low compression.

rob res /

sdsailor8 OP

Oct 10, 2020 10:31PM

@ggspeed,

The compression tester is good, i got the same results on my old cylinder.

I have read that when you use a compression tester it affects the results due to the extra hose that is atached to the head adding more CC's but don't know for sure if that is correct. I had a head gasket that i received with the kit and i installed it and then found out it was the wrong one it was 2mm in thickness so i used the one i had bought before when i bought a piston and rings for my old cylinder that one is 0.40mm but it did not improve the readings.

I will go ahead and check the head for flatness and see how it is.

Shouldn't the new cylinder be perfectly flat? or what they sell at treat is junk?

Re: Peugeot 103 LVS-U3 Low compression.

P D /

pdcomm

Oct 10, 2020 10:40PM

> rob res Wrote:

> -------------------------------------------------------

> @ggspeed,

>

> The compression tester is good, i got the same results on my old

> cylinder.

>

Gee , you think maybe your old cylinder was still good ?

Test the tester against a known good tester .

And , the little bit of hose making any kind of big difference is bunk .

It's a simple gauge to see approximately how much compression is present .

It doesn't matter if it a few pounds one way or the other .

Why do you think factory manuals state a given amount for optimum/desired compression , plus or minus as much as 10% ?

Re: Peugeot 103 LVS-U3 Low compression.

rob res /

sdsailor8 OP

Oct 11, 2020 03:39PM

@ PD,

Yes i maybe it was but it did have some scoring so i was thinking that it was one of the reasons for the low compression.

If i had another compression tester that i could use to compare that would be good but i don't. The compression tested could be defective even though is new i have hardly used it but i have had it for a long time. i will do "O" ring replacement on the adaptors and see if that makes a difference.

As far as the extra hose adding to the cylinder volume that is what i read so i am trying to find out the cause of the low cyl pressure.

The only thing i have not replaced is the decomp valve but i tested it when i removed the head and poured a little bit of water in the cavity where the valve was sitting and it held same when i did the compression test i sprayed some soapy water on top of it and not bubbles so that tells me that it is holding a seal.

Thank you for the input and suggestions

Re: Peugeot 103 LVS-U3 Low compression.

P D /

pdcomm

Oct 11, 2020 04:13PM

The soapy water is great for the bubble test , but , when testing the chamber seal from inside , remember that water is thicker ( about 30% more dense ) than gasoline and will hold where gas may not . Best to use rubbing or iso propyl alcohol which is much closer . (edited)

Re: Peugeot 103 LVS-U3 Low compression.

rob res /

sdsailor8 OP

Oct 11, 2020 11:43PM

@pd,

The way i tested the decompression valve was when i had the head removed from the cylinder and i inverted the head and poured a little water on the seating area of the valve and no water came out on the other end then when i had the head installed i did the soap bubbles test on the exposed area of the valve.

Today i removed the head again and checked to see if it was warped and it was a little so i sanded it to remove the uneven areas until it was straight(flat) then i installed it and did the compression test again and same results 60psi. The cylinder was fine and straight.

I am going to go to my local auto parts store and borrow a compression tester just to verify that mine is good.

I will update then.

Re: Peugeot 103 LVS-U3 Low compression.

rob res /

sdsailor8 OP

Oct 12, 2020 07:47PM

Update,

I borrowed a compression tester from my local auto parts store hooked it up and i got 90 psi but it started to loose compression so maybe that compressor tester is also defective or it is somehow loosing compression. I did not have that problem with my compression tested because it would hold the 60 psi so now what? install it or keep troubleshooting i should say that i only replaced the seal on the clutch side not on the ignition side (if it has a seal on that side i don't know) i am going to investigate.

Let me know if you have any comments or suggestions.

Re: Peugeot 103 LVS-U3 Low compression.

P D /

pdcomm

Oct 12, 2020 10:40PM

Compression testers use the same type core valve as are used in motor vehicle tire stems . If you have a core a core tool , try tightening the core of the tester and see if it holds better .

Re: Peugeot 103 LVS-U3 Low compression.

pat splat /

ggspeed

Oct 13, 2020 09:33AM

If its showing 90 then it should be able to start. Pull flywheel, service points, set timing, then squirt some premix in the hole and try to drill start.

MOPED ARMY

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