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oversize bores


Wimbledon37

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I am having problems with a P4 201 cubic engine. it is +30 over bored. i have replaced valve guides and have fitted new valves but when warm the engine is pumping oil out of the rear breather tube. I have removed the head and the bores seem quite oily. the rings were new when I rebuilt the engine (it came as two disassembled engines). Does anyone know if this engine can be rebored to +40 and if there are (or were) piston sets available. I am in the UK and cannot find any here!¬

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Sounds like something is wrong with the ring wall seal.

 

Someone may not have properly gaped the rings. I would pull all the pistons. Hone the walls to a proper cross hatch pattern. Place new rings in the bores. Gap them properly. Then place them on the pistons and put it all back together and see what you get.

 

Just FOLLOW the ring makers recommendation for breaking in new rings. Fire the engine off and IMMEDIATELY bring it up to 1000 to 1500 RPM. Do not let it idle.  Run it for at least 15 minutes or whatever the ring maker recommends.

 

James

 

 

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Throwing out ideas .... Several years ago I had a 4cyl 1991 Dodge shadow engine rebuilt. I took it to a garage who R&R the engine & delivered it to the machine shop.

It was a few days before Christmas, the machine shop was extremely busy .... They managed to get the car back before they shut down til the 1rst of the year.

I know TMI, just explaining the machine shop was highly recommended .... They made a mistake in their hustle & installed the rings upside down.

 

I drove it about 200 miles & it was using too much oil, I had to bring it back & they tore it apart, found their mistake & had the car back running perfect in 2 days.

 

I do not know if it is possible to install our rings upside down?

Seems that engine it was ... I could imagine possibly someone installing the oil rings & compression rings in the wrong order?

 

I'm going with the others here, some reason the rings are not sealing. I can see only 1 way to diagnose then choose a proper cure   :(

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I would do a compression and leak down test before tearing into it.   But since the head is off, take a look at that road draft tube.   A missing filter could cause an abnormal ‘drippage

 

 

if not that pull some pistons and check them out. Ring gap etc

Edited by kencombs
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19 hours ago, Wimbledon37 said:

when warm the engine is pumping oil out of the rear breather tube

A breather tube that is spewing smoke out of it, seems a indication that oil is getting past the rings and being burned & blown out the tube.

 

If oil is being dripped out of the tube, makes me wonder if so much oil is getting past the rings, no chance for it to burn & turn to smoke.

 

I would want to know, how much oil is the engine going through? ..... In my example above, was 2 quarts in 200 miles with rings upside down.

 

I wonder what rings are installed? .... I understand that Chrome Molly rings take longer to wear in & seal while modern rings seal almost instantly.

This could be normal if breaking in Molly rings?

 

It probably will be needed to know how much oil is being used ... I suspect that pulling the head & seeing oily cylinders it is a fair amount used.

So we are all jumping to conclusions on ring error ....  Depends how much oil is actually used.  .... Maybe it is normal?

 

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To answer your  original question  this block can be bored all the way to 3 1/4  (+ .125)

 

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I would take the block along with the pistons to a Machine shop and have it honed and have the pistons fitted to the bore and they be able to tell which rings to use. I can tell this that your rings are seating if you have oil on the top of pistons. Find a Machine in your area and call them and see what they suggest.

Happy Motoring

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I had a friend that had the standard piston in his 39 Desoto.  Egge was able to get him the standard sized pistons. But eggie uses a different set of rings for their pistons and not the chrysler ring sets.

 

His mechanis did a bottom end and installed the rings and the pistons. He ran the engine to break it it and di approx 200 miles on the car. When acceralting he noticed blue smoke out the tail pipe and hen taking his foot off the gas pedal also blue smoke out the tail pipe.

 

We think it might be the issue of the pressure and the oil getting to the exhust vales under more pressure becsue of the rebuild.  They are going to take the eninge apart to determine what the cause is for his issue.  He is also running  Castrol GTX 20/50 weight oil.  He ran with me to the Nat desoto convention and was  driving the engine at 60 MPH which I thought might have also been the issue. He had the bluw smoke prior to going on the tour.  Told him to keep the car at 50 mph and not put stress on the pistons

 

On his way home continued to run at 60mph and when he got home he noticed that he was down 3 qts of oil. Major issue with engine.

 

Will keep posted.

 

I ran my 39 Desoto at 50-53 mph and the engine has about 20 k on the rebuilt engine, did not burn any oil and got 16-18 mpg on my car.

 

Rich Hartungi 

 

.

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On 8/29/2022 at 4:15 AM, Wimbledon37 said:

Thanks to everyone for your answers. Much appreciated. i will start by pulling out the pistons and checking all the rings are the right way up!

 

thanks again

I think a proper procedure to install rings would include. .... Before ever installed.

You put them in the cylinder one at a time, use a piston to push them into the cylinder .... just squares it up. Then you measure the gap.

Just like setting points, there is a proper gap for your rings. ....... If the gap is to tight you then can file the ends to get the proper gap .... if the gap is too wide they may never seal.

 

Because of the force of the piston rods, the cylinders can wear into a egg shape. So if you check the ring gap at the top, then middle, then bottom of the cylinder .... will give you a good idea of how true your cylinders are.

We expect others to have already done these things during the rebuild ..... for whatever reason someone dropped the ball during the process & it is up to you to figure it out  :(

 

Just something else you can check at home without a machine shop.

Years ago it was common to bore a cylinder ten thousands over, then use std pistons with rings made ten thousands bigger.

Is it possible your rings are not correct size for your cylinders? .... same was done for pistons 30 over then add oversize rings .... you need too check this.

 

For some reason I thought it might be a good idea when you get the pistons out & start a new thread just for checking the rings & cylinders.

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Also check that the rings are 90 degrees to each other as well as the right way up......I have heard of 80thou over rings being available and I actually have 2 sets of 60 thou over rings still in their box.........lol... ..andyd

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Wimbledon37......just replied to your pm......I'll recheck the piston sets as I haven't looked at them for a while but from memory they are fine, piston rings are still in their individual paper packets..........I'll get back with the full specs etc........will take a couple of pics also, tho' will be a day or so getting the pics loaded into the computer as the computer expert(wife) is away till wednesday.......lol.......the ring sets were going to be used on the 230/3.25" bore engine I was building for the 41 Plymouth I had  but ended up selling and for whatever reason that escapes me now the ring sets got left behind.........anyway, will get back with details asap.........regards, Andy Douglas.  

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Wimbledon.......heres some details of both sets of rings..........I have made a slight mistake.......one set is 40 thou over.........the other is 60 thou over....anyway the details are as follows.......

 

The 40 thou over are McQuay-Norris Altinized Factory Type Set Piston Rings, 12 x3 &1/4 x3/32 COMP and 12 x 3 &1/4x 5/32 OIL, copyright 1938 McQuay-Norris

Part # 639 .040. packed in the original McQuay-Norris circular cardboard container with metal end caps, the rings are packed with a paper wrap with a basic instruction sheet.

 

The 60 thou over are McQuay-Norris Rebore Rebuild Expander Piston Rings, set # 4339, .060, Chr-Dod-Ply 42-47, .060 O.S., 12-3&1/4 x 3/32 COMP & 12-3 & 1/4 x 5/32 OIL.....the 60 thou over set are individually wrapped in waxxed paper with "Top,2nd,3rd & 4th" indicated on each set of 6 rings, the 2nd & 3rd rings each have what looks like a spring steel inner expander ring, packed in the Mcquay-Norris square cardboard box with each of the 24 rings in individual packets 

 

I have taken pics of both sets, however I am not smart enough to load the pics onto the computer, that will have to wait till my wife gets home, Wednesday........lol.........all rings appear to be in good condition, are not rusty or discoloured to my eyes and as mentioned I had intentions of using them in the engine build I was going to do........I trust this helps..........I had figure of $40 each set on them when I had them at a local swap meet..........anyway will get back with pics soon......lol.....BTW......my email is scaleautomobilia@yahoo.com which might be easier to contact me thru........andyd       

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Email again is   scaleautomobilia@yahoo.com  ...........retyped it holding my left leg crossed over the right & typing with my right middle finger.........lol.........who knows what makes this computer tick.....lol........anyway if you decide to bore out your block let me know....lol.......all good...andyd  

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