Hi everyone

Something that I thought I'd share with you that I seem to find a bit on heads (not just mini ones). This is a head that I had just started work on, and one of the exhaust inserts popped out of it. I was boring out the internal diameter to suit larger valves. When I do this on correctly installed seats, there is not issue. But ones that are dodgy installations sometimes move or pop out like this one. Obviously, machining an insert is never a good idea if you're going to be taking either huge cuts or reducing its thickness too much... if that’s what you need to do, then really, start from scratch and put a bigger insert in.

3 things that I think tend to be the issue are.....

1:- not enough interference

2:- people trying to install them with loctite

3:- people either chamfering the back or not putting a big enough radius on.




The correct interference for installing seats in cast iron heads is 0.004" per 1" of O.D ... or 0.1mm per 25.4mm So on the seats I tend to use which are 33.89mm in diameter, I use 0.13mm of interference.

How do we release loctite? We heat it up with a blow torch to break the bond. What happens to exhaust valve seats? They get bloody hot so if you loctite them in, chances are, after the engine has been run for a bit, the loctite will release.

When you're pressing in an insert, or any part with interference, the part is going to need a "lead in" or a "leading edge" so that it will go in. Otherwise it either simply won't go in, or it will broach the hole as it goes in, increasing the diameter of the hole and decreasing the interference.



What I am pointing to in this photo is a 45 degree chamfered edge that was put there as a lead in. It will work, it will provide a lead in.. BUT.. it still has an edge on it where the 45 degree angle meets the large outside diameter. That edge can still broach the hole. The best option is a smooth radius. Below are photo's of two inserts, a genuine one with a TAM part number and an oversize one right, if you look carefully, both have a radius.




Another strange one that I have seen is people peening loose inserts in. Or peening them to make them hold more... or something....



Again, not a great idea... you're creating uneven tension around the insert. You can peen holes to decrease their size, but you can't really do it here successfully or accurately. Usually the best way is by placing a large ball bearing (at least 3 times the diameter of the hole) over the hole and striking it, making it shrink around the top edge. This is fine in applications where you "Just need interference and it doesn't matter how much"... however, on a head, you would neither be able to fit a ball bearing that size over the valve seat due to the small size of the combustion chamber nor would it be advised due to the potentially catastrophic consequences of it not having enough bite. Best way to do it is the right way.... make sure you machine the shoulder to the right size for the insert.


Alex

thanks for the info .... shonky business

as an aside but related matter, do you know what glue is being used in some of the resleeved bores - i take it the idea that good glue doesn't risk deforming bore walls

this was a result of a seat falling out....

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did I tell you that I won a trophy?

Tops PK. Thanks for taking the time again. Of course you won't find me trying to do fine tolerance machine work.

I have your painting how-to printed out in the shed and I followed the instructions line by line on the weekend. Your contribution has been fantastic. Even a ham fisted desk jockey like me can get good results with your clear and thorough text.

Would it be bad to hope the other forum stays broken so the knowledgeable guys over there come back here?

M

On a similar topic, any cases where the cut out for the inset has broken into the cooling jacket, which may lead to combustion leaks past the seat and into the cooling system and thus overheating in a similar fashion to a cracked head?
I suspect I have a head like this. It was reconditioned with unleaded inserts, car started overheating, changed the head with a stock second hand one and all good. The “reconditioned” head is on the shelf.

Hey FNQ

I've got to be honest mate, this is the first I've really heard of it. To my knowledge the correct practice for sleeve fitment is dry with interferance as per manufactures specs. That said, sleeves don't get nearly as hot as exhaust valve seats so there may well be a product on the market that does the job. I won't lie, it makes it a hell of a lot easier putting together something thats interference if there is some sort of glue or something in there, because while its still wet, it helps lubricate the fit.




Is that one of your motors Simon? That would have sucked!






No worries M, how did it come up? As for the other guys coming back,, well,,, you'd have to talk to them about that You've still got plenty of great minds kicking around on here.. GR's been about a bit lately, and the Doc is usually on line, I think I saw 850man make a post the other day... And what about Matt Reed, come on, you've still got Matt Reed




Hey Indigo, yeah I guess that is possible.... however, there is a lot of meat under the seat and around it. The standard seat inserts are about 6mm deep with about a 4mm wall thickness. I can't say I've ever had one break into the water jacket, even when using oversize seats.. not saying its not possible but it would be bloody unlucky.... did you contact the machine shop that did the head? I've had one case where a valve let go and destroyed the valve seats and I had to weld the seat back up to restore it because I wasn't sure how much meat was left before I hit water, so I just welded it and machined it back to be sure..... I would hope that other professionals would do the same, you really want nothing but metal touching the insert, if its half hanging in the water jacket or something you can't be sure its going to stay put. I would have taken it back to the engine shop, that sounds a bit strange

Hi Phat,
Always got something good to show.
I think I have a head in the shed or had one that has been centre punched
around the seat. A lot of old timers and bush mechanics did that sort of thing
when they had no access to presses or machine shops and they just had to get the job done.

Centre punching or hammer peening for retention can work on steel, but it's a recipe for disaster on cast iron. It is so brittle it will break before the metal bends or flows at all.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

yep, my motor... bit of a pain...

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did I tell you that I won a trophy?

Hi Alex
When i have to sleeve cylinders 2/3 in a mini i glue them in this way it does not distort the bore next to it, i give them a thou .001 clearance press them in to step in the bottom and all's well.
The loctite that i use is 620 used for holding diesel sleeves in, and in saying that my race car engine has 4 sleeves in it which is better castiron than the original bores and gives a better seal for the rings.
Graham Russell

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"It's better to be not informed than ill-informed"

Ah, there you go. I didn't think it was out of the question on sleeves, just wasn't sure what the go was. Cheers.



Hi MG

Yeah, like the doc said, you can do it with Steel and it works.. but cast iron is a bit hit and miss. It will still work a bit... but its not really ductile enough, I wouldn't rely on it working

[/quote]not really ductile enough[/quote]
now there is a term I haven't heard since my 1st year apprentice days.............I love it oh the memories

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"Re-living my Surfing Past in a Woody"

not really ductile enough[/quote]
now there is a term I haven't heard since my 1st year apprentice days.............I love it oh the memories [/quote]

ductility, malleability

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"Show me the Mini!"

now there is a term I haven't heard since my 1st year apprentice days.............I love it oh the memories [/quote]

ductility, malleability [/quote]
Yep we are all getting old Mick, nobody worries now, they just hit everything with a BFH and put metric screws into UNF holes...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

ductility, malleability [/quote]
Yep we are all getting old Mick, nobody worries now, they just hit everything with a BFH and put metric screws into UNF holes... [/quote]


Speaking of metric/imperial stuff ups, I was feeling like a royal ass 10minutes ago measuring up a hole for a valve guide going "I need to buy a 11.906mm reamer.... 11.906mm reamer.. Damn it the closest one listed is 11.98 ".... And then I realised it was 15/32"