Twin cam Valve Guides.

[Grizzly]

Bit of an update, Well i have not fitted the guides (well sort of)

Before i stripped the head i tried the new Guides with the valves and found the Exhaust where spot on but the Inlets where a touch tight, so i reamed them in the Lathe before fitting so they where a nice fit, so next came the removal, i got the head warmed up to 150deg and the inlets where quite easy to knock out but when i got to the exhausts they where a bit of a mare. they where very tight even warm and as i hammered the drift they kept shattering and jamming the Drift in the guide but after a few attempts i got them out ok. (didn't like hammering the head with a lump hammer )

So i rewarmed the head back to 150deg and knocked the new guides in (no loose ones all took a bit to fit which was good) but after fitting i found out why there supposed to be reamed after fitting, non of my valves are even close to going in. I did think maybe i had disformed the end with knocking them in? but whats odd is they don't fit at either end? ts like they have been compressed by the head..... So i'm at the point where i'm thinking about how to put the reamer down the guides (do i set the Pillar drill up or do it by hand??) but first i think i'll have a go at measuring how much they have changed but how the valves won't even start i'd say a fair bit.

O and for anyone reading this about to fit there own, don't make the fitting drift too tight, i didn't think there would be much movement so i didn't pay much attention to sizes just as long at it was smaller then the od of the guide and the locating pin was smaller then the id, problem was it was a little to tight as when i knocked the new guide in i couldn't get my drift out i think with the guide id shrinking a bit it had gripped the drift quite well. Easy fix but i wasn't expecting them to close up quite as they did. (if any of they makes sense)

[elansprint71]

It never crossed my mind that anyone would ream the guides before fitting them, or I might have given advice to that effect.
I used an adjustable reamer, that's got to be better than a variety of fixed sizes because you can feel when the bore is getting to the correct size. With "solid" reamers it is easy to find that too much metal has been removed.

[rgh0]

Bit of an update, Well i have not fitted the guides (well sort of)

its like they have been compressed by the head.....

Yes that is exacly what happens the interference fit in the head compresses the guides a fraction and given the tight clearances required on the valve stems you need to ream after fitting.

cheers
Rohan

[Grizzly]

It never crossed my mind that anyone would ream the guides before fitting them, or I might have given advice to that effect.
I used an adjustable reamer, that's got to be better than a variety of fixed sizes because you can feel when the bore is getting to the correct size. With "solid" reamers it is easy to find that too much metal has been removed.

I do agree but i thought about this quite a lot, i reamed them out first for the simple reason i could do it very accurately on the lathe (i mean the valve stems are .3095" and my guides where .3100", felt very nice in the guide) also i have had run ins with Adjustable reamers in the past making tapered or off round holes. The way i look at it, if i want to get a very tight tolerance and 100% sure the hole is round and no taper to it etc it has to be done by machine and with the correct reamer.

But all that said i am not in a situation where i may have to cut them by hand, i have a .3090 reamer that was to tight but if its done by hand may fit. I may be getting too involved in this but i will be gutted if this thing smokes still when it all goes back, so i'm getting every thing as good as i possibly can.

[Grizzly]

Bit of an update, Well i have not fitted the guides (well sort of)

its like they have been compressed by the head.....

Yes that is exacly what happens the interference fit in the head compresses the guides a fraction and given the tight clearances required on the valve stems you need to ream after fitting.

cheers
Rohan

Yes but thats unfortunate, thing is i'm shocked at how much they have closed up. the original plan was to ream them on the lathe to the perfect fit then chase the guide after fitting but they have really moved allot and now there in of course i have a problem accurately measuring them (don't have a small enough internal micrometer )..... O well was worth a go.

[rgh0]

You can get a set of bore gauges to measure the guides ID for a reasonable price from many suppliers, a normal set will cover from around 5 mm to up to 100mm so you can measure every important bore on an engine accurately. You select the one that covers the range you want to measure and insert then expand fit then remove and measure with a conventional micrometer. This is the only way to properly check the guide bore clearance with the valve stems along its length, both new as you ream and for worn guides to decide if need replacing.

cheers
Rohan

[Grizzly]

I do have a set but mine start at 10mm which is typical, i have a small one on order with long handle so i think its all going on hold until it arrives.

[Grizzly]

Bit of an update, Well i have not fitted the guides (well sort of)

its like they have been compressed by the head.....

Yes that is exacly what happens the interference fit in the head compresses the guides a fraction and given the tight clearances required on the valve stems you need to ream after fitting.

cheers
Rohan

Out of interest, does this only happen with bronze guides? i only say that because i removed the Iron ones and they didn't appear to get more loose on the valve stems?

[elansprint71]

[quote="GrizzlyOut of interest, does this only happen with bronze guides? i only say that because i removed the Iron ones and they didn't appear to get more loose on the valve stems?[/quote]

I would be very surprised if the ally head could exert enough force on iron guides to make any difference to the bore size.

Of course, when your engine gets hot, the clearance between valve-stem and guide changes again! This way lies madness.

[Grizzly]

I would be very surprised if the ally head could exert enough force on iron guides to make any difference to the bore size.

Of course, when your engine gets hot, the clearance between valve-stem and guide changes again! This way lies madness.

I was surprised how much the Bronze guide closed up to be honest, i was expecting maybe a bit of disformation where i had knocked it in but shocked at how much it had actually moved.

Heat.... yeh i have enough problems getting my head round all this when its cold i will be happy if i can just stop it smoking....... Belive it or not it had crossed my mind to cut some grooves in the new guides so i could fit valve stem oil seals (can't see any reason why they wouldn't work??) but after doing much reading i was put off the idea, seems tight guides and no oil doesn't mix.

[rgh0]

To allow for hot versus cold as best I can I run the inlets at the bottom end of the Lotus clearance spec range. My logic is that the inlet valve stem stays cool and expand not much while the guide expands with the head heating up so the clearances open up and you want it as tight as possible while cold.

For the exhaust I set it to mid range on the Lotus spec as the stem gets much hotter and may expand more than the guide and you dont want it siezing and clearance is not so crtical with oil leaks as it is for the inlet whee you have a large vacuum pulling oil down the stems.

People have fitted stem seals in the past but not really needed if you get the clearnces right in the first place.

cheers
Rohan

[Grizzly]

Well i have now done the guides,reamed them and Ground in/fitted the valves but i have come across another issue, i measured the valve clearances before i stripped the engine (was still bolted to the block) and they where on the large end of the tolerance, the thing is i was expecting the clearances to tighten up slightly which me regrinding the valve seats but i have just test fitted the cams and the clearances have become much bigger 14-16 thou. So does having the head fitted to the block cause the valve clearance to change?? I was planning on building the head up as much as possible before fitting it but it looks like i need to get it on and bolted?

Does that make sense? I think i need to do some more reading.....

[elansprint71]

Well i have now done the guides,reamed them and Ground in/fitted the valves but i have come across another issue, i measured the valve clearances before i stripped the engine (was still bolted to the block) and they where on the large end of the tolerance, the thing is i was expecting the clearances to tighten up slightly which me regrinding the valve seats but i have just test fitted the cams and the clearances have become much bigger 14-16 thou. So does having the head fitted to the block cause the valve clearance to change?? I was planning on building the head up as much as possible before fitting it but it looks like i need to get it on and bolted?

Does that make sense? I think i need to do some more reading.....

I'll leave the answers to those more qualified than I.
My recent experience was that only two of the valves still required the same thickness of shim, the rest were all over the place. Also I had to piddle about a bit and take the cams off again a couple of times to re-do the clearances, after bolting down the cams and re-checking. I had the benefit of a tobacco tin full of all sizes of shims, which makes things much easier.

[rgh0]

If you fitted new valves then different stem lengths from valve seat face compared to the old valves could increase the clearance.

regards
Rohan

[Lotus fan]

Pete.......................
Nice to know you've got a tin full of shims for me

Ian F.