[XolieX]

hey guys,

my dad who is a mechanic and i tried to guess what's wrong with my car. and he said it could be a burned valve.

my dad said to test that you put a piece of paper at the tail pipe and see if it sucks it in. well, both o my tail pipes do that.

can it still be a burnt valve even if it doesn't do that in.

 

[XolieX]

oh yea, my dad only said that is a cheap easy way to do it. but to compression check it to make sure.


is doing the sucking in paper thng accurate?

 

[393Clevor]

Does he work on bikes?

 

[XolieX]

no he doesn't work on bikes. i hope that wasn't a sarcastic remark.



olie

 

[Wildcat]

A guy I know who was a mechanic in the late 60's does the same tailpipe test. Athough he just feels with his hand instead of paper. Personally, I think there must be something to it, if a valve is burned, there should be a "suck-back" of air. But I think you really have to develop a feel for what is normal "suck-back". My 302 with dual exhaust "sucks-back" a little, as does every other one I've felt. I think you have to look for excessive "suck-back", but you need experience to do that. I'd go with the compression test, it's easy and more reliable to the less trained hand. Good luck.

 

[393Clevor]

On 2002-02-23 18:55, XolieX wrote:
no he doesn't work on bikes. i hope that wasn't a sarcastic remark.



olie

No, it wasn't. I only asked that because I have only heard of this being done to bikes. The tail pipes are shorter and there is only 1 to 4 cylinders. This test is more accurate on bikes then a car.

Do a compression test wet and dry.

 

[Peltor]

I would recommend a cylinder leak test. Then you don't only know if it's leaking or not, but where it's leaking and how much.

 

[Wildcat]

Do a compression test wet and dry.

What's the difference between a wet and dry compression test?

 

[393Clevor]

I have done wet and dry test on lots of cars more older VW's than anything. What a dry test will give you is the actual cylinder pressure. The results of a dry test will give you a good idea of the engine condition but not only the valves will alter the results but the piston ring condition will have an affect on the results as well. The wet test will tighten up the piston ring wear and will not let it leak by. So you can tell if it's rings or valves. After a dry test you got a difference of 50 PSI on one cylinder. Then you did a wet test and it was 3 PSI then the rings are the reason for the difference in that cylinder.

You still have to tear it down

Use the same amount of oil in each cylinder and crank it over 3 or 4 times before using the gauge. This will let the oil get all over the rings and out of the cylinder before you close it up. Don't use to much oil I use like 2 squirts from an old oil can 5W 30 is ok.

If I'm not straight about this please correct me.