Stiff pistons! not sure what i've done wrong.
Turbo Mini Forums

Hi guys, I'm very new to building engines and learning all of this as i go along. Still i'm determined to build my engine myself. I seem to have run into a problem in putting the pistons back in and not sure where i've gone wrong.

I'm currently rebuilding a metro turbo block. When i stripped it down the pistons and the crank all turned freely before i took then out. I've run one of those three legged deglazing tools down the bores and bought what i beleive to be standard size piston rings. ( These http://www.minispares.com/Product.aspx?pid=34929) I put new bearings on the crank a put that in. This turns freely, but then i put the new rings on and went to put the pistons back into the bores. They were very hard to drive into the bores it took a lot of effort and when attached to the crank were still quite hard to move. Now i'm led to believe that they should move fairly freely. Sorry for the long winded post wanted to give as much info as possible. Anyone help with this matter is very much appreciated! Thanks

New rings on a fresh honed block do give a considerable resistance.

You did 'Gap' the rings first before you installed them on the pistons??

If not then id be taking the pistons out, removing the rings and checking the end gap to see if its correct.

I'll admit i didn't gap them. Like i said complete beginner. Bit of a silly mistake i guess. So is there a method to measuring the gap? How do i adjust it if its wrong? File the rings?

im sure there is a specicific torque you can set a torque wrench to, put it on the end of the crank if it turns before 'clicking' its a good indicaton thats nothings too tight. I couldn't quote the figure though, maye someone else knows?

Its definately worth gapping the rings first though!

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1/4mile in 13.2sec @ 111 terminal on 15psi

Well i've just gone out and removed all the pistons and placed the rings into the bores on there own and measured the gap. Is this the correct method? If it is then the gaps i had were within the tolarences in the manual. Yes the bores were all oiled before i put the pistons in. I did expect a bit of stiffness due to the honed bores but i can't even turn the crank by hand and thats with only one piston in the block! With all four in it would be impossible to turn judging by the first one.

fit the piston and rings, see if you can move it up and down the bore by hand, if so is shouldn't stop the engine turning.

ohh the rods have a corect way round, the big end is ofset to one side, if ou put it the wrong way the rod will bind on the crank.

guess how i know

could be a main or big end beaing making it tight to turn if your sure the pistons are all ok.

no longer a series, but still 1.3 turbo.

Yea i got the offsets the right way round on the pistons. I can't move the pistons up and down the bores by hand, even without them connected to the crank. I'm beggining to wonder if maybe i should have just payed someone to do this for me. I've clearly done something wrong somewhere. I really wish i was more of a patient person lol.

i wouldnt stress too much, just pop the pistons out and gap them

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Have you definately put the right rod caps on the corresponding rod?

When minispeed did my machining they mixed mine up even though i numbered them when i took the engine in!

As they are all line bored a slight mix up WILL bind the crank and make it really hard to turn!

I swopped mine around one by one, testing the friction by turning the crank each time, and mine spins perfectly now.

All end caps were put back on the correct pistons and all pistons will be in the correct bores. They are stiff when they are not connected to the crank. I've checked the gaps in the rings with the rings placed into the bores on there own. Is there another clearance i should be checking other than the one at the gap in the ring. Could the finish of the bores be the problem? i used one of the hones you attach to a battery drill and ran that up and down the bore, but just enough to remove the glaze.

When you ran the hone up and down the bores, did you make sure that you kept it moving so that the grinding marks were at a reasonable angle?

It could be stiff if you let the hone just run in the bore.

Ideally the hone marks should be at 45 degrees although I found this very difficult to do. I managed about 20 degrees and my engine was quite stiff.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Where abouts are you?

If your local I'd be happy to come give you a hand....

Alex

AlexF

AlexF

I oiled my rings and bores!

And used graphogen on all the bearings purely because if i used graphogen on the rings it would have been tricky to get lube amongst all the rings and look really messy!

Edited by richminiturbo. on 22nd Sep, 2006.

Of coures you grease rings, skirts and bores. If not, the pistons and bores would be ruined before you even start the engine.

Didn't "my fist turbo" have a similar problem the other week. He could not get his oil control rings in at all!

I'd put a piston in with just the oil control ring and see if that's causing the problem.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Hi thanks for all the replies. I live in Essex so not sure just how local i am. Probably not. Yeah when i put the pistons and rings in everything was literally soaked in oil. The oil control ring sounds hopeful as it was different to the origonal metro ones. Instead of two rings and a spring it has the spring inside a larger ring kinda combines the other two that would be in the origonal, if that makes sense? I'll have to make another attempt later with just the oil control ring. Will report back later with my findings.

where in essex? PM me if you like.

Edited by Sprocket on 22nd Sep, 2006.

The oil on rings and piston skirts will be gone in a flash once the engine fires up. Then everything will be back to "normal". You don't think pistons run dry in an engine do you? Well, they don't!

As much as it pains me to admit it, I am with Vegard on this subject.