[vishnuharih]

Hello Friends,

I had a piston seizure on my Std 350 '73 model running a 40 oversize bore. There was a loud rattling noise and upon dismantling the cylinder I could see fine lines all along the bore and 3 groups of vertical seizure marks on either sides of the piston. I had the seizure in the middle of a trip and had to cover almost 800 km's to reach back. There were no issues with the compression or fuel consumption after the seizure. It was returning an average of around 40kmpl with a Mikuni 28mm round-slide fitted with a jet of 85. The oil level too did not show much of a depletion, or rather showed normal depletion that happens after a long ride.

The options I am now left with is to either shove a sleeve into the cylinder & go for a std bore or to replace the cylinder and piston. The shops here are now offering a cylinder with a 5 ring piston instead of the 3 ring piston I was using. I cant make the choice as I am left with a few unanswered questions.

1. The difference between the 5 ring and the 3 ring piston, the advantages and disadvantages of the two kits. If I am correct, the 5 ring piston assembly was introduced towards the last years of the std 350 by the company. My mechanic back in my hometown cautions against using this new cylinder on the older models as it causes excess smoke and talks about some seating issues.

2. Shoving a sleeve into the old cylinder and going for a std bore. Is it inviting more trouble or is it a safe practice. Reading through various forums on the internet suggests that shoving a sleeve into the old cylinder causes engine overheating, loss of compression and power. Is there any truth in this assertion.

It would be really nice if someone can help me with the queries or direct me to resources, here on this site or elsewhere.

[B O V]

Originally Posted by vishnuharih

Hello Friends,

I had a piston seizure on my Std 350 '73 model running a 40 oversize bore. There was a loud rattling noise and upon dismantling the cylinder I could see fine lines all along the bore and 3 groups of vertical seizure marks on either sides of the piston.

Looks like we both are in the same situation.

After a long ride a few months back I started hearing mild rattling sounds under load. Got the time to open her up a few weeks back.

My '83 too was running on a size 40 oversize, I've just given the head off to the lathe for new sleeve. I do not know if it will increase the chances of a seizure.

Fear not , I'll confirm all the details and the queries you've asked with my trusted mech.

P.S- Has your bull been worked on in other states? My mech mentioned that the Mechs in Kerala rarely go for a 40 oversize.

Regards,

BOV

[vishnuharih]

Thanks for the response BOV.

The bull hasn't been worked on by outside mechanics. When it came into our hands, it was already running a 20 oversize bore with a lot of smoke. Our mechanic gave us the option for a 40 bore and he is located at Kollam. We even had a 60 bore on another bullet, an '81 model. Though the barrel looked dangerously thin, it is still running good. It has been almost two years since that bore though it would have run just around 10k km's until now.

[Suresh Stephen]

Though it is a standard practice that to change the piston and or cylinder after an engine seizure, If the oil and fuel consumption is not affected, there is no reason why the same assembly cannot be used further. Using a fine file, you slightly file down the seized portion of the piston before assembling it back. It will work. Replace it if only the performance is deteriorated. Having said that, why did the piston seize?. Were you maintaining very high speeds for a long time? Or is there is an oil supply issue? Or was the initial piston was set with lesser clearance than the specified value? Generally mechanics have a tendency to set the piston slightly tight and expect the set to run in to actual clearance during service. Believe me, 99% mechanics do these jobs just by the feel of the assembly. NO measurement of the cylinder/piston is taken while reboring. If the performance is not deteriorated and there is not issue in the oil system, if I am in your place, I will take a chance and assemble the set back after the filing down of the seized area(Personal experience with various old machines)
Suresh

[ArizonaJim]

I tend to agree with Suresh Stephen.

Often after a partial engine seizure, using a very fine grit sandpaper to smooth the piston in the scuffed areas will allow it to be used again.
Using a "wet/dry" silicone carbide sandpaper in a 320 or 400 grit if it is available is recommended.

If the cylinder bore is not deeply scratched, the same sandpaper can be used to remove any material that has been deposited by the piston. When doing this the sanding should be done by twisting the hand while moving it up and down the bore.
The idea is to create a crosshatched pattern on the bore.
This will not only remove the scuff marks but will serve to aid the piston rings in their breaking in process.

This process should be attempted before any thought of reboreing or replacing the cylinder is made. Many times the damage looks much worse than it really is.

Speaking of the piston rings, these should be replaced with new ones.

As Stephen noted it is imperative to determine the cause of the problem.
If it was oil related, that must be fixed before starting the repaired engine.

[vishnuharih]

Thanks Suresh & Jim for your suggestions. I will try this out before I go for a replacement or a re-bore.

As for the reason for the piston seizure, I have nothing to blame except myself. It was not an issue with the oil circulation, but that I maintained high speeds without giving a thought to my engine.

As for the initial piston clearance, it was kept a little tight and my mechanic had told me the same. The bull has done around 20k km's and the running in was properly done for achieving the clearance.

There is no issue with the performance, but the rattling noise is what disturbs me. It's too loud and I feel threatened with it ! That was the reason why I thought of a repair/replacement.

Also, after dismantling the cylinder, I noticed that there is a sideways movement of the piston with the pin in place, and it stroked the sides of the crankcase, probably the cylinder skirt when it is in place, which is what I believe is making the rattling sound. If I am correct, the piston is to make a movement only along the axis of the rotation of the crank, and not perpendicular to it. If that is the case, does it mean that there has been a deformation to the piston where the pin holds it to the connecting rod because of the overheating and seizure?

The cylinder bore is not deeply scratched and the lines are very fine. 320 and 400 grit sandpapers are available and I think I will go with a 400 to make the crosshatched pattern on the bore.

Apart from that, I am very curious about the 5 ring and the 3 ring piston as well as the advantages and disadvantages of the two kits. Any information on that?

[vishnuharih]

The new piston rings are probably 4 instead of 5. And the seating issue is with the combustion chamber and not the crankcase.That's what the shopkeeper told me today. Any more details on these two different kinds of piston & cylinder kit.

[Suresh Stephen]

Dear Vishnu,
Looks like the piston was set very tight and you must have been driving very carefully till now. The company recommended piston to bore clearance is 0.075 to 0.100mm while setting and the service limit is 0.175mm. Check the piston diameter and bore diameter and then replace the piston only if the clearance is more than 0.175mm. It is a good idea to replace the rings if there are scuffing marks on it. The recommended end gap is 0.20 to 0.33mm. Clean the scuffing marks on the piston and do the cross hatch in cylinder bore as Arizona Jim has suggested, You should be fine.
In case you decide to change, Fixing a sleeve and using a std piston is a normal work so long as you take of the recommended clearances. Or else, if budget permits, go for a factory original cylinder/piston kit thereby the clearances are taken care of.
A piston seizes due to uneven expansion due to the non symmetric shape of the piston. That is why it was suggested to file/sandpaper down the affected area.
I thought the 5 ring piston is used in the UCE engine, if so it may not a right part for this engine.

All the best
Suresh

[ArizonaJim]

The so called 5 ring piston rings are used in the UCE engine. I don't know about the AVL or what may be available for the Cast Iron engine.

Actually, the 5 ring set piston only has 3 ring grooves.

The two top piston rings are solid compression rings like one normally thinks of when they think about piston rings.

The oil ring in the bottom piston ring groove is not a solid ring with slots or holes thru it.

Instead, the oil ring consists of three different pieces. The top and bottom parts are very thin solid rings which are separated by a very thin, wavy (corrugated) strip of material.
The waves of the corrugation are in line with the direction the piston travels.

This type of oil ring has been in use in all types of engines for decades so it is nothing new.

[B O V]

Originally Posted by vishnuharih

I will try this out before I go for a replacement or a re-bore

Well, I got my re bored cylinder back.

Reading through various forums on the internet suggests that shoving a sleeve into the old cylinder causes engine overheating, loss of compression and power.

I asked my mech about this, he said that this happens if done by a sloppy workshop, inaccurate measurements et al. He assured me I will not face any issues. According to him it should be running better than ever.

Just gave the head for valve seating. Dumping the old valves and getting new ones. New ones are slightly different in design from the old ones.

Getting the bottom end opened up tomorrow probably.

Costs

Reboring - 2000 Rupees

New Piston (standard)- 535 Rupees (India Pistons limited)

Regards,

BOV

P.S - I'd have taken pictures but I've got a sorry excuse of a camera

[nickoo]

Hi, I have a 2004 Std 500 (cast iron) that needs an engine rebuild and i am looking for the complete cylinder kit + rings for the bike in Delhi/NCR. Can anyone help me here please?

[Randhawa]

If you come down often to Patiala then I can ask for you at the RE spare shop in Chandigarh or the dealer. But few years ago I heard it was going for double the price of MRP from the dealer itself. PM me if you need help from Chandigarh, I can just try.