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Old 18th March 2009, 08:49   #1
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Default CNG Accent, Done 35k - Does it need an overhaul?

Hello mates,

I have a hyundai accent, 2006 converted to CNG done 35K.

On my last trip to Rajasthan one of the sparkplugs broke, i would somehow blame overheating, i did manage to take the broken plug out but some porcelin fell in the cylinder but the car started. after a thousand kilometers or so the car started but did not pickup the throttle easily. it was like it is having an asthma attack. back in noida i opened up the head to see that one of the intake valve seats was damaged by the porcelin. i got the valves changed, but i noticed some play in all the pistons. i don't think it is normal.

Do i need an overhaul? should i use an oversize pistons or get cylinder sleeves and use the original size?

Also, let me mention that before the spark plug thing, the oil filter started leaking. by car was running on about 750ml less oil.
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Old 18th March 2009, 09:08   #2
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If the play in pistons is even reasonable, I think they will damage the block. I suggest you visit the Hyundai Authorized Service center. I know they are very eager to catch big customers ( the customer who come with a big job that will earn them money ), but the fact that pistons have play is not normal from what I have seen.

Before going in for the oversized pistons think twice and figure out what was the real reason for the original pistons getting play.

Best is to take the car to Hyundai Authorized Service Center.

EDIT : I think this thread should be in this section : Technical Stuff - Team-BHP
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Old 18th March 2009, 09:46   #3
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^Thanks, i would prefer going to Arush or Raj Kapoor for the job. Hyundai service centers are a no no, here the clearance that the manual mentions -
Piston - to - cylinder wall clearance :
0.02 ~ 0.04 mm (0.0008 ~ 0.0016 in.)
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Old 18th March 2009, 12:59   #4
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Your title was a shocker. A petrol accent getting an overhaul at 35K kms is unheard of. Dont go for the oversized pistons as it may effect the overall performance of the car. Try the Hyundai A.S.S and get a feel from their suggestions. AFAIK, they really dont fleece their customers.
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Old 18th March 2009, 13:03   #5
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Avi, if you take a look at the circumstances under which this situation arised you would realised that there is no need to be shocked.

This could happen in any petrol engine and no need to single out a particular brand as such.

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Originally Posted by mobike008 View Post
Your title was a shocker. A petrol accent getting an overhaul at 35K kms is unheard of. Dont go for the oversized pistons as it may effect the overall performance of the car. Try the Hyundai A.S.S and get a feel from their suggestions. AFAIK, they really dont fleece their customers.
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Old 18th March 2009, 13:08   #6
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Quote:
Originally Posted by suren181 View Post
Avi, if you take a look at the circumstances under which this situation arised you would realised that there is no need to be shocked.

This could happen in any petrol engine and no need to single out a particular brand as such.
Sure, i noticed that but what could be the reason for overheating in the first place? CNG usage?

@Saintsinner, were you completely on CNG during this highway drive?
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Old 18th March 2009, 14:33   #7
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I would suggest to use the sleeves and stay with the recommended piston size.
If the cylinder is damaged, then you may have to shell out some good amount on labour and parts.

There should be some very good Hyundai service centres in your part of the country. Have the car inspected by them and get the quote.
Also approach good engine mechanics, tuners in your area. Get quotes and recommendations for the job.

Once you get the picture clearer, decide on the job. DON'T HURRY!!
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Old 18th March 2009, 15:41   #8
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well, yes my car primarily operates on CNG. it has done about 20K on CNG of which 2-3K would be on petrol. but i don't agree with CNG doing this damage.

could it be the oil? at 30K hyundai serviced my car, decarbed the engine and put mineral oil(earlier it was synthetic) after a while the oil filter started leaking and i was running on less oil for about 600-700 kms

are pistons supposed to be sealed tight with the cylinder? if i open the head and move the piston sideways with both my thumbs, then i can see some play.

also if it really needs overhaul, shouldn't the engine be burning oil? the spark plugs do not show any sign of oil. but the pickup has decreased, on petrol it jerks sometimes.

should i post pictures of the plugs?

Zak, the hyundai people get the boring work done from outside. the person who does boring, i know him. hyundai will not use sleeves, they put an oversize piston. i'll get some quotations. the car works it is just sluggish.
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Old 18th March 2009, 19:33   #9
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From what I have heard, running CNG reduces engine life. But we are yet to face this and we have done around 30K kms on CNG in our Maruti 800 ( 92 model ).

How much less oil, do you mean very very less oil ? Then yes, lack of lubrication might have caused damage.
If the car is too sluggish even in petrol, take the car to service center.
Dont go for oversized pistons. If the play in pistons is not sorted out and oversized pistons are put in, the block will be further damaged.
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Old 19th March 2009, 16:49   #10
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have you got a compression test done?
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Old 20th March 2009, 00:14   #11
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First thing you should do is already mentioned. Get a compression test done.

another one is easy. Rev the car hard after attaining ideal temperature. If you see white smoke from exhaust, you definitely need an overhaul.
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Old 20th March 2009, 04:05   #12
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^ no smoke at all. still hits 160-170 kmph on road
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Old 23rd March 2009, 13:25   #13
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get a compresion test done it costs a mere 500 bucks from any A.S.S. also ask them to give u wet and dry readings. pistons should not have any play. if you have the head opened. try putting some oil on the top surface of the piston. if it disappears over a couple of hours you need a ring job.
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Old 23rd March 2009, 15:45   #14
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this is a useful vid:

YouTube - 49 Diagnosing Faulty Compression 76 MGB

if you have the head on - check compression in all the cylinders. all cylinders may not have low compression. the ones that do, pour some 10w30 oil in through the spark plug hole. immediately check compression again in those cylinders. if it's the rings, you should see compression increase the 2nd time. if it's not the rings it could possibly be the head gasket.

Last edited by silver_shadow : 23rd March 2009 at 15:49.
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Old 23rd March 2009, 17:50   #15
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The best thing is to take in to an Auth service center. Get it diagnosed and then if it is too high a bill you can also check other outlets.

You can come to Safdarjang Hyundai in Gurgaon. They are very good and professional. Let me know if you need help and I can give you the number of a person there.

Another point is, if you do decide to come, you would need to be there at around 8 in the morning else it can get very crowded after that.
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