Pistons are now really tight in the cylinder

Simeon · Post by **Simeon** » Tue Jun 16, 2009 11:10 pm

Help
Putting my Rover V8 back together and now the pistons are really tight in the bore causing the crank not to turn

Other than cleaning the cylinders up and re-ringing nothing has changed. I remember when I took it apart the pistons fell out of the bores. Have I got the pistons mixed up? are they in the correct orientation?

Being new to this engine re-assembling mallarky I read that the thrust face of the piston points reaewards on the left bank of cylinders and thee right bank points forwards. My question is as the pistons have no visible marks apart from A which I presume is the piston size how can I tell which is the thrust face? Do the small end caps have a certain orientation?

Excuse my outburst but I'm all flustered as everything was going so well.

ppyvabw · Post by **ppyvabw** » Wed Jun 17, 2009 1:05 am

I'm assuming you have the same pistons, and everything was labeled when it came out so the rods go back in the same place. If you view the engine from the front, the thrust face is on left hand side of each bank. So on the left bank (from the front) the thrust face is towards the outside of the engine, and on the right bank (from the front) the thrust face is towards the middle of the engine. So the left hand side of the cylinders from the front.

Yes, if you have put the bearing caps on the wrong way round, or on the wrong rod that could seize it up too I think. Everything should have been labeled as it came apart so it goes back in the same place.

mgbv8 · Post by **mgbv8** » Wed Jun 17, 2009 8:02 am

Have you fitted the old pistons with new rings?

If so, did they push down the bores ok, or were they really tight to push in?

Did you make sure that you have the dimple marks on the con rods facing each other on each journal?

ChrisJC · Post by **ChrisJC** » Wed Jun 17, 2009 8:12 am

I would think the problem is either the main bearing caps or the big end bearing caps being swapped.

Your only real fix is to remove things one by one until you find out where the problem lies.

Chris.

Pocket rocket · Post by **Pocket rocket** » Wed Jun 17, 2009 9:36 am

For the avoidance of doubt, the pic shows the dimple (sometimes referred to as a "rib" or "boss" in some manuals) on the con-rod.

[/img]

CastleMGBV8 · Post by **CastleMGBV8** » Wed Jun 17, 2009 9:41 am

Just to help clarify things, the conrods are offset to centralise them in the bores, fit them the wrong way round and the con rod small end will be off centre on the gudeon pin and pressing up against the bearing area in the piston and will be trying to bend the conrod.

As Perry states the conrods have dimples on the sides which should face each other, also the rod big ends have one side with a machined flat face which should be the dimpled side.

Use plenty of engine assembly lube when reassembling the engine.

Kevin.

ChrisJC · Post by **ChrisJC** » Wed Jun 17, 2009 11:46 am

Am I right in thinking that the piston / rod combo's are handed, so although all eight pistons are the same way in the block, the rods are different depending on cylinder bank....?

Chris.

Eliot · Post by **Eliot** » Wed Jun 17, 2009 12:40 pm

I would remove the big end cap and see if the piston moves up and down reasonably well. I assume you put plenty of oil around the rings and in the bore when fitting them..

Simeon · Post by **Simeon** » Wed Jun 17, 2009 9:01 pm

Thank for all your input guys!
I possibly think it's a combination of all the things you suggested. The conrods have never been disconnected from the pistons so once I get that right then the pistons will be facing the correct way. Main bearing bolts were binned and ARP studs used but the crank did move freely with no pistons attached. Will get another chance to play on Friday and will let you know what happens

Simeon

ppyvabw · Post by **ppyvabw** » Thu Jun 18, 2009 1:43 am

Simeon wrote:Thank for all your input guys!
I possibly think it's a combination of all the things you suggested. The conrods have never been disconnected from the pistons so once I get that right then the pistons will be facing the correct way. Main bearing bolts were binned and ARP studs used but the crank did move freely with no pistons attached. Will get another chance to play on Friday and will let you know what happens

Simeon

If the rods have been put in the wrong places, or the wrong caps put on the wrong rods then I would suggest re assembling the engine with new shells as I think they may have been damaged if it didn't go together properly.

unstable load · Post by **unstable load** » Thu Jun 18, 2009 3:21 pm

If you are using the old pistons with new rings did you clean the ring grooves in the pistons before fitting the new rings? If ther's crud under the new, bigger rings then it will definitely tighten things up.
I find a broken (old) ring makes a good scraper as it's the right size for the groove. Be careful not to score the grooves though as it will set up possible fracture points.

Simeon · Post by **Simeon** » Sat Jun 20, 2009 12:30 am

Good News Guys and Gals

There all in with the engine turning nicely (Manually that is). The problem was not enough lube and boss marks pointing at every direction on the compass apart from the way they should have.

Once again Thanks for your help. Until the next snag

Simeon