stiff engine

[cadetchris]

yes i know the engine is suffering from a serious problem and i am working on that to fix it.

as for the rings, what should the end gap be then???

the duplex chain i fitted because the the single chain on the engine was very worn as where the teeth on the cogs. i did remove the two bolts behind the lower cog, countersunk the holes and replaced them with the correct countersunk screws.

the pistons are the originals to the engine (except number 3, which i replaced with a piston of the same size)

the bores are standard bores, the pistons are standard. the are standard (esm said so), the bearings are standard and have been replaced. the conrod are the right way around, as are the pistons. the fly wheel isnt snagged on anything behind. the clutch works beautifully and disengages on command of the peddle.

having had my head under the engine this morning, without the sump on, everything is tight, in the correct place, torqued down properly.

i have checked everything i can possibly imagine and more. i am now going to take off the head, take out each piston, remove the rings carefully and inspect the bores. i am also going to measure the pistons themselves to see it they are the same on the head and skirt. if they are not (which i am suspecting) then that's where we have our problem. as to why they could be different, i am not sure. no doubt some body will know why, but i am out of ideas

[bmcecosse]

Ok - I wondered if the bolt heads could be snagging the gear - which would make the engine 'tight' to say the least. So - it 'must' be down to rings - since you are re-using the same pistons - except one - so take that one out first.

[cadetchris]

just checked the pistons,

the crank moves very well without them attached, and they where a dog to get out. the skirt of 3 pistons has a bulge to one side, which could explain why they didn't move freely within the bore, haven't the foggiest how this has happened, they where a bit tight going into the bore to begin with, but i thought that was just due to the lack of normal lubrication (i did use lots of oil to slide them in)

i also thought i could use the pistons from the other engine, but upon removing them, 2 of the are severely scoured down one side, which explains why that engine was u/s.

so, do i get (if i can) two pistons and use the 2 good ones from the other engine or do i just take a big breath, open the wallet and fork out £100 or so for a new set of pistons?

[aupickup]

check ebay for pistons normally a few on there

[katy]

Quote: "presuming that i have standard pistons, standard bores and standard rings (which i do) measuring the end gaps of the piston rings would merely academic and serve no use."

No, it wouldn't, it would be common sense and good engineering practice. When installing new rings they should ALWAYS be checked for proper end gap, whether it's new pistons or used, rebored or not.

You asked what the ring end gap should be, IIRC you are working with a 1098 engine.
IF so, according to the manual, the ring gaps should be:
Compression rings: .007"-.012"
Oil rings the same if they are scraper rings.
If they are Dualflex rings the gap is: .012"-.028" for the side rails
and .100"-.150" for the side spring.
HTH

[bmcecosse]

So - how could the pistons have become 'bulged' ? Did you clamp them in a vice to fit rings - anything like that ? Are you sure you put the pistons in the correct bores ? It would be a shame to buy new pistons -and not do a rebore. Try for a cheap set on ebay - or from the forum - but I think you need to KNOW why they bulged like that - so it doesn't happen again!

[kennatt]

[quote="bmcecosse"]So - how could the pistons have become 'bulged' ? been bugging me that,never seen it before

[Ratbag]

*just read all the thread* comment removed by me!

[Bradmoneypit]

Not sure if this helps, but when I rebuilt an old seized engine I assumed the old con rods would be OK and didn't bother checking them before fitting. When I tried to turn the engine over it was extremely tight. I removed all the big end bearings and one at a time replaced each turning the engine over when each was fitted. If it gets difficult to rotate the crank after one or more of the con rods being fitted, it is likely that when the engine seized the con rod over heated and distorted. They may have distorted in the past even if the engine wasn't seized as well ( lack of oil, poor oil or water circulation in the past etc)

Might be worth doing this check, if the problem is found, you can either get the con rod reprofiled, or better still get another set of con rods.

Another thing to check is that the con rods in the right order, if not they may be catching on the inside of the crank case.

Finally are the crankshaft shims in place, if not they may be dragging against the side of the bearing, this is unlikely but worth a quick check.

[Kevin]

just checked the pistons,

the crank moves very well without them attached, and they where a dog to get out. the skirt of 3 pistons has a bulge to one side, which could explain why they didn't move freely within the bore, haven't the foggiest how this has happened, they where a bit tight going into the bore to begin with, but i thought that was just due to the lack of normal lubrication (i did use lots of oil to slide them in)

Any chance of posting up a picture of the bulging pistons so we can see them..
As a matter of interest they should be able to move in the bores without lubrication and not be tight.
As regards the replacement rings I assume you used the stepped ones and not the standard ones to take into accound the wear lip in the bores.

[cadetchris]

strangely, and against all logic, it appears i was wrong about the bulged pistons. i did break the skirt on one piston whilst undoing the timing chain nut and i assumed that owing to the pistons being very tight in their bores, i "thought" that they too had been pulled out to one side with the over zealous nature of putting the engine back together.

I took out the pistons to day and thankfully the bores are all shinny and unmarked, so no re-bore there then. I then removed the piston rings and gingerly pushed each piston into each pot, to my utter amazement, they moved in them freely and with ease, therefore using scout logic, it cannot be the pistons binding on the sides of the bores. i also gave the crank a couple of terms and it was beautifully smooth (as one would expect), so now that means my attention must turn to the offending pistons rings.

i bought these ones from a well know company

http://morrisminorspares.co.uk/shop/pro ... 89681950b9

i assumed that standard pistons, standard bores = standard rings, apparently i am wrong at this. having read back through the thread i does mention a few times that one should measure the gaps at the end of said rings. how does one do this? i tried, but owing to evolution (shakes fist) i am unable to hold piston, compress rings with fingers and measure the rings with a wee feeler gauge at the same time. any ideas?

i have ordered a new set of pistons and rings from the very nice spares bloke, as my pistons where a little tatty to begin with and i should of replaced them when i did the engine in the first place. would these new pistons and rings solve my problem or will i have made yet another expensive mistake?

answers on a postcard please to the usual address

[Jefftav]

Hi, I'm no expert but it might be worth checking the bores are standard so that you know the pistons with rings will fit. If you can't manage yourself there might be a local engineering workshop who could check for you - just to give peace of mind when building it all back up.

[katy]

To check ring gap on worn cylinders. (Simple)

1) Put ring in it's cylinder, make sure that it's right side up.
2) Use a piston to push the ring down. (Using a piston squares the ring w/the cylinder.)
3) Push the ring down to the unworn part of the cylinder.
4) Measure the gap w/feeler gauge.

If not enough gap, put the ring in a vise w/the gap just above and parallel to the top of the vise, file a bit off the end of the ring to increase the gap, GENTLY file the 4 edges of the end you just filed to remove any burrs.

Recheck the gap. Repeat as necessary.

Do this with ALL the rings for their respective cylinders any time you are putting NEW rings in, whether the cylinders have been rebored or not.
If you check all the rings and only one out of the whole bunch needs to have it's gap increased, that one makes the whole process worthwhile.

[cadetchris]

right,

job for when i get the pistons tomorrow, then hopefully hopefully the car will go, unless i have burnt out the starter by trying to turn the very still engine over, one step forwards, 3 furlongs back.

[bmcecosse]

I have checked rings in the past - and NEVER had to do any remedial filing! Be sure to put one piston in at a time - connect it all up - with lashings of clean oil, and check the engine turns over EASILY before moving on to the next piston.

[cadetchris]

ok, two camps here. to check and file and not to file. which is best then?

[bmcecosse]

Oh yes - check! Only file if you need to - I have never needed to, the gaps have always been fine.

[Kevin]

I took out the pistons to day and thankfully the bores are all shinny and unmarked, so no re-bore there then. I then removed the piston rings and gingerly pushed each piston into each pot, to my utter amazement, they moved in them freely and with ease, therefore using scout logic, it cannot be the pistons binding on the sides of the bores. i also gave the crank a couple of terms and it was beautifully smooth (as one would expect), so now that means my attention must turn to the offending pistons rings.

i assumed that standard pistons, standard bores = standard rings, apparently i am wrong at this.

answers on a postcard please to the usual address

Right first thing you should have done is see what was stamped into the top of the pistons, for example
STD = standard, .020 = 20 thou oversize, .40 = 40 thou oversize & so on
As you say the bores look smooth have you confirmed that there is not a wear ridge near the top of the bore on all sides the best thing to check with is a finger nail as its very sensitive to any imperfections.

[billlobban]

I just fitted a new set pistons and rings to my newly rebored block the rings were perfectly gapped and didnt need adjustment although I'm sure I was just lucky. As the engine builders bible says if it takes you all day to check and gap the rings then take all day - it'll be worth in the end

[bmcecosse]

No - you weren't lucky - if you buy new pistons with rings they are invariably correct!