27 replies to this topic

[.998TANGO.]

hello

i recently bought a 1275 "reconditioned" enigne off someone on here. soon as the engine was started there was plooms of blue smoke coming out the back. i left the engine in used it everyday for a week and the smoke continued and had to top up the oil everyday. now taken it out. i think it was the valve guides causing the issues as the two inlet ports were very oily. Now i have the head off is there anyway of testing that the rings are sealing without a strip down and rebuild? (i have very limited student funds) so i can confirm its the guides and get a new head sorted so i can have the 1275 power back

thanks elliot.

[Cooperman]

Before stripping the head off you should do a compression test and a cylinder leak-down test.
This will help with the diagnosis, although badly seated valves can give a lack of compression just as well as worn bores/rings.
If the engine is still in the car and running, run it at low revs with the oil filler cap off. If it puffs smoke out of the filler hole, then it's rings and/or bores.

[bmcecosse]

It's 'never' the valve guides! This is a straw grasped by many - worn guides have only a tiny effect on smoke/oil consumption. You need to pop the pistons out and inspect the bores and the state of the pistons/rings and bores.

[Guess-Works.com]

It's 'never' the valve guides! This is a straw grasped by many - worn guides have only a tiny effect on smoke/oil consumption. You need to pop the pistons out and inspect the bores and the state of the pistons/rings and bores.

I would not say never...

An engine I had the pleasure of having to rebuild ( less the head ) new bottom end, crank pistons rebore etc.. blew smoke like a goodun, was only when I pulled the head apart that it was obvious that the valve guides were hopelessly worn, you could actually waggle the valve around in them... that added £200 to the bill for new valves, guides and the reseating of the valves.

However, back to the question, the only way to be 100% sure about a piston ring fit is to take one off the piston and stick it down the bore and measure the gap, and to do that it's an engine strip down.

[minispud]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block, also have a look at the bores for cross hatching, if there are not visable then it could be that the rings are not sealing against the bores, thus allowing the engine to burn oil.

[Sprocket]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

Edited by Sprocket, 06 January 2010 - 07:03 PM.

[minispud]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

What you are checking for is "Piston-to Bore" clearance. The top of the skirt should be between 0.0026 to 0.0036 inch's or in mm's 0.066 to 0.081 any more then this then it's a strip down job.

[R1minimagic]

Well, there can be wear in a number of areas, not just the circumference of the piston ring, so to check properly you need to measure a number of things, such as

bore wear profile and appearance (e.g. scoring and polishing)
ring sticking
ring breakages
ring thickness
ring scoring and polishing
ring weight
piston skirt condition
top land, 2nd land, 3rd land dimensions and condition
top groove, 2nd groove, 3rd groove dimensions and condition
deposit rating in all the areas above

so to do a proper job you need to strip it all down!

There could be very little wear but if the rings are stuck or broken you will still burn oil!

[minispud]

hello

i recently bought a 1275 "reconditioned" enigne off someone on here. soon as the engine was started there was plooms of blue smoke coming out the back. i left the engine in used it everyday for a week and the smoke continued and had to top up the oil everyday. now taken it out. i think it was the valve guides causing the issues as the two inlet ports were very oily. Now i have the head off is there anyway of testing that the rings are sealing without a strip down and rebuild? (i have very limited student funds) so i can confirm its the guides and get a new head sorted so i can have the 1275 power back

thanks elliot.

Do you know if the engine had any mileage on it between the time it was Recon'ed and you buying it, and when it was recon'ed was the block rebored or did the bores get honed, the reason being if you put new rings in old bores they will not seal and you will get blue oil smoke.

[.998TANGO.]

hello

i recently bought a 1275 "reconditioned" enigne off someone on here. soon as the engine was started there was plooms of blue smoke coming out the back. i left the engine in used it everyday for a week and the smoke continued and had to top up the oil everyday. now taken it out. i think it was the valve guides causing the issues as the two inlet ports were very oily. Now i have the head off is there anyway of testing that the rings are sealing without a strip down and rebuild? (i have very limited student funds) so i can confirm its the guides and get a new head sorted so i can have the 1275 power back

thanks elliot.

Do you know if the engine had any mileage on it between the time it was Recon'ed and you buying it, and when it was recon'ed was the block rebored or did the bores get honed, the reason being if you put new rings in old bores they will not seal and you will get blue oil smoke.

he said he used it for 400miles and was perfect..

thanks for all responses looks like im going to be stripping it down and rebuilding.

[Sprocket]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

What you are checking for is "Piston-to Bore" clearance. The top of the skirt should be between 0.0026 to 0.0036 inch's or in mm's 0.066 to 0.081 any more then this then it's a strip down job.

Yes but you are not understanding, or you do not realise that the measurement you are talking about is bellow the oil scraper ring, which means you have to get a 3 thou feeler gauge down past three piston rings, and if you can do that, the engine is useless. the 'crown' of the piston is always a smaller diameter than the 'skirt' of a piston.

Also piston clearance is measured at the bottom of the skirt on thrust sides of the piston. Pistons are not round

Edited by Sprocket, 06 January 2010 - 08:26 PM.

[minispud]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

What you are checking for is "Piston-to Bore" clearance. The top of the skirt should be between 0.0026 to 0.0036 inch's or in mm's 0.066 to 0.081 any more then this then it's a strip down job.

Yes but you are not understanding, or you do not realise that the measurement you are talking about is bellow the oil scraper ring, which means you have to get a 3 thou feeler gauge down past three piston rings, and if you can do that, the engine is useless. the 'crown' of the piston is always a smaller diameter than the 'skirt' of a piston.

Also piston clearance is measured at the bottom of the skirt on thrust sides of the piston. Pistons are not round

The skirt is the side of the piston and the crown is the top, the clearance is at the top of the skirt and the bottom skirt clearance is different, it's between 0.0006" to 0.0008". These clearances are for a 850 cc 85H engine, the others have difference clearnces

Edited by minispud, 06 January 2010 - 08:46 PM.

[Sprocket]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

What you are checking for is "Piston-to Bore" clearance. The top of the skirt should be between 0.0026 to 0.0036 inch's or in mm's 0.066 to 0.081 any more then this then it's a strip down job.

Yes but you are not understanding, or you do not realise that the measurement you are talking about is bellow the oil scraper ring, which means you have to get a 3 thou feeler gauge down past three piston rings, and if you can do that, the engine is useless. the 'crown' of the piston is always a smaller diameter than the 'skirt' of a piston.

Also piston clearance is measured at the bottom of the skirt on thrust sides of the piston. Pistons are not round

The skirt is the side of the piston and the crown is the top, the clearance is at the top of the skirt and the bottom skirt clearance is different, it's between 0.0006" to 0.0008". These clearances are for a 850 cc 85H engine, the others have difference clearnces

Still dont see how you will measure the top of the skirt when its below three piston rings?

[minispud]

If you got the head off of the block, what you can do, is check with some feeler gauges how much gap is between the piston and the block,

This does not work when the rings are still on the pistons. The crown of the piston is much narrower than the reast of the piston, where the piston clearance really matters. You cannot get a 3 thou feeler gauge past the rings and if you could, the engine is shot!

What you are checking for is "Piston-to Bore" clearance. The top of the skirt should be between 0.0026 to 0.0036 inch's or in mm's 0.066 to 0.081 any more then this then it's a strip down job.

Yes but you are not understanding, or you do not realise that the measurement you are talking about is bellow the oil scraper ring, which means you have to get a 3 thou feeler gauge down past three piston rings, and if you can do that, the engine is useless. the 'crown' of the piston is always a smaller diameter than the 'skirt' of a piston.

Also piston clearance is measured at the bottom of the skirt on thrust sides of the piston. Pistons are not round

The skirt is the side of the piston and the crown is the top, the clearance is at the top of the skirt and the bottom skirt clearance is different, it's between 0.0006" to 0.0008". These clearances are for a 850 cc 85H engine, the others have difference clearnces

Still dont see how you will measure the top of the skirt when its below three piston rings?

The skirt starts at the point where the crown finishes, so the top of the skirt is the bit above the top ring and not below the bottom ring, a piston only has a crown and a skirt, there is no other bits

[Sprocket]

Ok I understand now, thanks for explaining that.

In the nicest possible way, I think you need to revise on your piston technologies

Edited by Sprocket, 06 January 2010 - 10:25 PM.