Small crack in Combustion Chamber

[xebec]

Hi,

I have recently taken the head off my 1971 Gt6 in order to lap in the valves due to compression problems and have come across this problem. Please see photo.

What are my options here or is this terminal and requires a new head?

Thanks & Regards,

Ken

[JohnD]

Xebec,

That's typical, not common , but I regret terminal fault. 

Repair could be tried, but welding cast iron is a skilled job (=expensive), needs the work to be heated very hot, and a lot of work to restore the normal shape afterwards. In such a highly stressed part of the head, unlikely to be successful.

Sorry!

John

[Pete Lewis]

a specialist welder  may take this on but i agree with John , best get a replacement  head 

many many years ago i found this on a nice 2000 mk1 we got it in the factory and it was welded up it lasted for many miles until sold 

but that was a freebie,  you may pay more for a repair (risky) than a replacement head 

PETE

[xebec]

Hi,

Thanks for your replies, can you advise on best place I can get hold of one. I have the early type GT6 Mk3 with flat pistons.

I would more than likely have to make a trip to the UK to get it but that is not really a problem. I live in the Netherlands by the way.

Regards,

[Pete Lewis]

Try TRGB for a used unit   in  Somersham     or any used supplier,  add costs of the  need a bit of refurb.

costs example  exchange recon  from Canley  heads mk1 and mk2  £385  plus surcharge  mk1£45  mk2   £101

pete

 

[Pete Lewis]

https://www.canleyclassics.com/triumph-gt6-mkiii-cylinder-head

to get the correct head its engine number controlled , click on the part numbers  down  below the details 

where all the changes are listed  they will ship it out to you .

have a feeling the surchage wont get refunded on a cracked unit

Pete

 

[Nick Jones]

Dependent on the depth of the crack it might possibly be resolved with valve seat inserts though made difficult by the closeness of the valves and a bit of a desperation measure!  Another head is the best option.

Suitable heads can come from a range of cars; this useful list on the New Zealand Triumph Club site shows the various possibilities

http://www.triumphclub.co.nz/?page_id=653

It is possible (usually) to skim down the heads from 2.5 and domed-piston 2L engines though best avoided if you can as quite a bit has to come off and there is some risk of break-though into water ways.  These are more common these days.

You could try Chris Witor.

Nick

[xebec]

Thanks all for your inputs, very much appreciate it. Cheers.

[xebec]

Hi,

Still looking at possibilities for a head for my early Mk3 GT6.

Canleys look the best bet at the moment however awaiting a reply from them on availability etc.

I have in the meantime another contact here close by who has various 2500/2000 heads but not the serial number 517528 that I am after but he has the followiing numbers:

516816, 219016, 218225

Could someone please advise if any of these would be suitable for my engine as I am a bit out of my depth when it comes to what would be the best solution here.

My cars Engine Nr KE254.HE. 1971 RHD GT6 MK3 flat top pistons.

Appreciate any help, Regards, Ken

[dave.vitesse]

Ken -

Numbers ---  516816 = TR6 IP head. 219016 = 2500S Saloon head. 218225 = Late GT6 (domed piston) head. All would produce a low compression.  

As you say the 517528 is the correct one.

Dave

[Nick Jones]

You could use any of those but all will need a huge skim.  Usually they will take this without "finding water", but not always.  I have a 219016 on my Vitesse engine. It has a different port profile behind the inlet valve and gives the best flows as standard, but is also the thickest so needing the biggest skim.

The thinner heads are getting harder to find now.

Nick

[Ian Foster]

I thought Mr Jones would be along soon !

I had an almost identical crack on my Mk2 head (No. 1 cylinder  by any chance?......) and it was considered terminal, although I have retained the head in case someone invents super glue for cast iron at some time in the (distant) future.

We used a 219015 TR6 head, with unleaded seats and reworked ports etc. and ultimately a skim that took it 0.020" under the original GT6 depth which gives a compression ration of 9.9:1. Also opened up some of the water jacket holes to match the GT6 head/block as these were not all present on the TR6 head.

I have information on chamber volumes etc available but not currently to hand.

(photo of new head attached)

Hope this helps.

Ian

[xebec]

Hi Dave, Nick, Ian,

Thanks very much for your advice. The crack by the way on my head is in cylinder 6, so it is now one mighty big doorstop.

I am leaning towards a recon head from Canleys at the moment with an advised lead time of approx 6 to 8 weeks. 

I have one final chance and that is Chris Witor as have just emailed him to see whether he might be able to help. (thanks for the idea Nick).

I have even toyed with the idea of a different engine but I think that is going a bit too far at the mo....I will have to see how it pans out.

Thanks again, Regards, Ken

[Nick Jones]

Yep, usually seem to crack on 1 or 6.  Guess they must run a bit hotter.  Something to be aware of is that both the 219015 and 219016 heads have smaller exhaust valves as standard.  This doesn't make much practical difference if intending to have unleaded seats fitted as they can easily be opened out to take the larger valves in that process (or you can keep them smaller if wanted) - it does mean they are less likely to be cracked - which I presume is the reason why these later heads had the smaller valves.

Nick

[NonMember]

The smaller valves also improve air velocity and thus fuel mixing at low speeds, which gives better economy on a low-revving engine like the 2500S at the cost of marginally less top-end power.

[xebec]

Hi,

No joy with Chris Witor as he has none at all however, he suggested skimming down a 3.400 head. I tried to find out from him which of the heads I could get hold of locally (516816, 219016, 218225) would be more suitable but I think he is now on Holiday.

He sent me a link to the head app chart: https://www.chriswitor.com/cw_technical/head_applications_chart.pdf

I have seen on the chart that the 516816 has the same raised number of 308351 as my head and also a rear water slot. I have also been doing a lot of searching and reading and have found this: http://sideways-technologies.co.uk/forums/index.php?/topic/702-compression-ratios/  which states: " I have a TR6 cylinder head casting number 308351 stamped 516816, this head is 3.41" thick, to machine this down to a CR of 9.5 for a 2lt GT6 you would need to remove 120thou. This is assuming that the chamber is standard and the pistons are flush with the top of the block"

I would  be very grateful for opinions on this and also what is the situation if I would use the 219016 head without the rear water slot?

Thanks very much. Rgds, Ken

 

[Nick Jones]

As I mentioned above I have a 219016 head on my Vitesse engine.  It's been on since 2008, fitted to two different bottom ends, having been used on both the original Mk2 Vitesse block and now on a late block originally from a 2.5 saloon, without any problems.  Not convinced that slot or holes makes any difference.  Cleaning the water jacket out at the back of the block around #6 cylinder is probably more important.

My head has had a massive skim and is very thin under the spark plugs, but this is partly because I was unwise enough to remove some material from the combustion chambers and partly because I wanted higher than standard CR.  I forget what the current thickness is, but could possibly measure it.  I

The chambers are the same shape on all the heads so simply reducing the thickness to 3.300 inches should get you close.  Only sure way is to burette the chambers as valve heights have a significant effect.  The 219016 is supposed to give the best inlet flow in unmodified form.

https://www.chriswitor.com/cw_technical/inlet_port_2.pdf

Nick

[xebec]

Thanks Nick,

I will go for the 219016 head and get it skimmed to 3.300 inches. I assume that I can use the standard pushrods and the non recessed payen head gasket which I bought ready to put the 517528 head back on.

Rgds, Ken

[Nick Jones]

38 minutes ago, xebec said:

Thanks Nick,

I will go for the 219016 head and get it skimmed to 3.300 inches. I assume that I can use the standard pushrods and the non recessed payen head gasket which I bought ready to put the 517528 head back on.

Rgds, Ken

It works for me!  With the current engine I even have had the block decked so there is 0.005" piston "pop-up".

Nick

[Unkel Kunkel]

Firstly, a disclaimer : This is certainly not  a technical answer to the problem -    a historical diversion at most .

The pictures brought back a  memory of the very hot summer if ‘76  when my work found me working in Norwich. 

Sweating and very  despondent, I was staring at   something very similar  on the head of my ‘71 GT6.

I was short of money.My outgoings were out of balance from my income which was very poor   even  then - and quite unbelievable  to  most  people now .The only option was to put the  head back on and keep my fingers crossed.

Long after uncrossing my fingers, 2 years on and a few thousand further ,it was still running really well - brilliantly in fact.

I sold it - to the person who had sold it to me.

We remain good friends.

[xebec]

Hi,

I have now collected the head that I am going to use 219016. It looks as though it has hardly been used

and looks new however, it did not come with valves, springs, collars etc.

i know which valves I need (ex 159872) (Inlet 146128) but have no idea whether it should have single or double springs and what collars to use.

Please could someone point me in the right direction so I can move forward in getting this head completed? Thanks very much.

Regards, Ken

[Pete Lewis]

Whats wrong with the springs you took off the failed head, WSM gives some load lengths and free lengths if they are ok  use them

Cant see manuals as on hol in sunny IOW

Pete

[xebec]

Hi Pete,

I don't think that I can use the springs off the cracked GT6 head as according to rimmers the springs have different part numbers whether double or single.

The single ones that I have on the GT6 head do not match with the numbers on the 2500S head parts list (according to rimmers) and therefore it leaves me with trying to figure out which ones to use. I have a WSM for the GT6 but not for the 2500S and have tried to search for one online without success.

Thanks for your input and have a good holiday.

Regards, Ken

[NonMember]

The springs should be compatible. The choice of double vs. single springs depends whether the engine is likely to get revved a lot (GT6) or only ever lugged up to 3000 RPM (2500S). So by the time you've skimmed that head to the right compression, it's a GT6 head, not a 2500 one, and should take the GT6 springs.

[xebec]

1 hour ago, NonMember said:

he springs should be compatible. The choice of double vs. single springs depends whether the engine is likely to get revved a lot (GT6) or only ever lugged up to 3000 RPM (2500S). So by the time you've skimmed that head to the right compression, it's a GT6 head, not a 2500 one, and should take the GT6 springs.

Hi, Thanks for your input as really appreciate it. This will of course save me some money so very pleased I can use them.

Cheers, Ken