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RedRooster

Holed piston

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Following on from page 76/77 of the what have you done to your car this week.

I broke mine, with a holed piston, whats also bizarre is the exhaust valves have made themselves cut outs on the pistons to a depth of 2mm.

So at the moment looking at new pistons & exhaust valves, plus checking the cam timing.

The bore on no.2 has ali embedded in it, i am hoping that will clean up with a hone.

 

 

 

 

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:huh:That really is most odd.  I now need to try and remember where I recently made the bold (and rather too sweeping) statement that the Triumph small 4 and 6 cylinder engines are non interference engines so I can go back go back and correct it.  Clearly this is NOT true for the domed piston 2L!

Having thought about it some more (but not drawn myself or Alan a picture, sorry Alan) I have decided that your cam timing must be retarded as the piston is getting up there before the exhaust valve has closed far enough to be out of the way.  Stretched chain?  If the chain has been stretching gradually it might mean that you pockets have formed gradually and explain why you haven't just bent the valves.....  Though I can't help thinking they may had suffered a bit!  Or is there a rod-stretching 9,000 rpm missed gear incident you are keeping secret? :tongue:

Nick

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Ah you got there before me, finally realised that it was a picture of a domed piston, I'm just so used to flat pistons I had forgotten they used them on the MK3 GT6 so that they could use the TR6 head casting without machining down.

Couple of idle thoughts, don't suppose the head was machined to up the compression ratio by machining to a thickness for flat top pistons, i.e. someone didn't realise domed pistons were being used, or that a given head thickness was for flat tops.

As to gradual formation of pockets and retardation of cam,  Slipping Vernier Adjustment Sprocket?  or possibly slipping crank shaft sprocket? have see a few threads recently of poor woodruff keys chattering, wearing until the sprocket can slip?

If just badly timed cam then I suspect that the valves survived so long as it was the exhausts closing (not the inlets opening!) as the piston came up so the piston probably just gave them a nudge in the right direction, they weren't fully closed so there was room, I'd suspect that it would have put compression load on the push rods (have they bent a tiny bit?) and load on the closing ramp of the cam lobe which may also be worn, but its in the place where it would have very little effect on cam or engine performance.

Going to be interesting to find the real cause to this one.

Alan

PS. Nick I think your comment about non interference was on one of my threads where I commented I had accidentally time #1 valve not #1 Inlet Valve, or perhaps a similar thread where someone had done the same. As I said its easy to forget about domed pistons when all you usually see is flat. 

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18 minutes ago, oldtuckunder said:

PS. Nick I think your comment about non interference was on one of my threads where I commented I had accidentally time #1 valve not #1 Inlet Valve, or perhaps a similar thread where someone had done the same. As I said its easy to forget about domed pistons when all you usually see is flat. 

More recent I think..... within the last couple of weeks or I would have completely forgotten about it.  As it is I've only forgotten where..... :ermm:

I agree with your thoughts on contributory factors to valve survival.  I have to say that I have never before seen marks like that (in flesh or pictures) where it wasn't a result of the demise... but I think it's largely unrelated.  Mind you, I've not seen a Triumph piston burnt like that either. 

My boss has a complete matching set of X-flow pistons to remind him why a misplaced "40" in a MJL table is a very bad thing.  He's got some aluminium blobs found in the sump too!  It just stopped dead in a cloud of smoke apparently!

Nick

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I found that my valves hit the domes on an engine, fortunately during a dry test assembly.    It's a while ago, but I think it followed a severe, CR raising skim of the head, that lowered the head so much that the push rods were too long.   Memory tells me that then I had the cam shaft reground, reducing the base circle and enabling the OE push rods to be used.    But that shouldn't be the problem here.

You are too severe on yourself, RR.   A holed piston causes massive amounts of white smoke.     know, I've had one.   I think you have  'only' lost all seal on the pistoon with a chip out of the edge, that has disabled the top ring.     Still needs a new one though.    If you can restore the bore wall, then ask me - I have some ddome topped pistons I'll never use!

JOhn

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Thanks for the offer of the pistons, they are +30.

The engine was built up around 15years ago by me & the engine builder so correct CR etc..

Looked at the head gasket again, absolutely perfect?

Took a couple of exhaust valves out & straight as you like & the stems have zero wobble in the guides so looking good there.

I can't remember if i put a vernier cam sprocket on this one, probably did as done it to quite a few engines, if i did & that has slipped then it could explain the problem.

Biggest worry is the bore on no.2 as that has a small groove in it now.

Cheers

Brad

ps

i also turned an engine to no.1 exhaust valve in my youth, something i never have forgotten.

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Well got the sump off in situ, that was interesting...

No.2 piston was very reluctant to come out, when it did i could see why as the rings were welded to the piston. Also one side of the piston looks like it has melted & the other side is missing the cir-clip, so between those two the cylinder was well scored, did a hone, then another, then another to try & tidy it up.

Got the Mercer bore gauge out & set it to a +30 bore then ran it past the damaged sections & the gauge kept going round! so it looks like i need at least 180 thou over sized pistons, which in reality is a new block, BF.

Anyone know of where to get a short engine?

My engine builder of choice is in Doncaster if that makes any difference.

 

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2 hours ago, RedRooster said:

Well got the sump off in situ, that was interesting...

Skinned knuckles and GTX hair conditioner?:huh:

That poor piston.......:pinch: Ouch.......!  Very bad news about the bore damage.  Are the others ok?  I know it's somewhat irrelevant in the context of recovery, but I'm very curious about the root cause and were it purely timing related I'd expect to see some signs on other cylinders with that one being that bad.  Blocked main jet in the carb barrel feeding #2? Also, you mentioned water loss from radiator and increased oil level (water in sump?) but with the head gasket looking (as you said) pretty much pristine, what is going on?  Was the water loss first with #2 being the first to suffer due to local hot spot?

If just one bore damaged then a liner is an option?  Not preferred maybe, but possible.

Don't have a spare block at this point I'm afraid.

Nick

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On the TSSC there is someone selling an engine & box but you have to be a member to get the details, anyone here help with that?

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13 hours ago, Nick Jones said:

 

what is going on?  Was the water loss first with #2 being the first to suffer due to local hot spot?

If just one bore damaged then a liner is an option?  Not preferred maybe, but possible.

 

Possible that if #2 was getting that hot, that there is a crack in cylinder wall that let water into sump?

Re liners, I think I have seen a few threads on TR6 forum about people having complete new liner sets fitted, haven't the faintest idea on cost, and suspect a complete S/H engine may be cheaper.  If crank etc all OK may be worth keeping your eye out for any 6 cylinder block as anything post 68 should be interchangeable, stripped incomplete engines sometimes come up quite cheap.

Alan

Still dying to find out what the cause was, as Nick said that's some horrendous valve/piston interference wear! and a good clue to anyone rebuilding a six pot to go for flat top pistons, and rework the head to suit, as unless you actually drop a valve it should be virtually impossible to get valve/piston interference with them. 

  

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https://www.ebay.co.uk/itm/Triumph-2000-MK-1-Vitesse-GT-6-BLOCK-flat-top-block-secondhand-NOTE-DELIVERY/163038623334?hash=item25f5dbf666:g:sMEAAOSwax5YwHYt

Not a mk1 block - clearly has equal length studs and they look bigger than 3/8"....... Also has rod clearance slots in the bottom of the bores which the earliest blocks don't have.  It is reasonably early as it doesn't have the strengthening rib along the bottom.  Can't tell if it's a flat side or bubble block.  Curiosity is that it's been on the angle-grinder diet with part of the engine mount bosses cut away and the engine number ledge gone.

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2 hours ago, Nick Jones said:

Also has rod clearance slots in the bottom of the bores which the earliest blocks don't have.  

My 68 late MK1 block has the rod clearance slots!  and a number of MK1 blocks have had the the studs enlarged to take the MK2 head.

Someone has put a fair amount of effort into that block, wonder from the engine mount rework if it was destined for a special or something, otherwise no idea why you would reduce the engine mounts to two bolts.  Also interesting that all the casting marks have been ground off as well, looks like someone was trying to save every ounce.

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22 hours ago, oldtuckunder said:

Well that was an absolute bargain!

Sure was.  Probably get double that for the TBs.

 

22 hours ago, oldtuckunder said:

My 68 late MK1 block has the rod clearance slots!

Interesting.  The block I first started with for the Vitesse engine "rebuild"definitely didn't yet appeared to be Mk2....  It was also noticeably lighter that the late one I ended using.

 

12 hours ago, RedRooster said:

Has anyone used Denis Vessey in Barnetby for engine work?

No personal experience.  As ever, online you get mixed reviews but people whose opinion I respect seem to think he's ok!

Nick

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The new block seems to be a goer so getting it round to Dennis's place now.

Decision time soon for the  block colour, the RedRooster has had a signal red block since i restored her, looks fantastic at shows when clean but shows every oily mark, so question is for the garage Queen do i do that again or go black because as the saying goes, once you've gone black theres no turning back.

RR

On 5/14/2018 at 10:23 PM, Nick Jones said:

 

 

No personal experience.  As ever, online you get mixed reviews but people whose opinion I respect seem to think he's ok!

Nick

 

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Did it come with or without Main Bearing Caps?  Even if with, unless clearly marked, I would be tempted to get it line bore honed. Its as cheap to get it honed as it is to get it checked, normally same set up on same machine.

Alan

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From the bay of evil pics main caps were included. 

All the Triumph engines i have worked on have had the caps numbers etched on so shouldn't be a problem.

RR

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