Valve Guide Loose in Head - Options?
Discussion
PeterBurgess said:
. Occasionally we find sintered guides which do not need reaming on fitment but very rarely!
Peter
I'd say in general that bronze guides compress more during fitment than iron ones but yes most guides need a ream once they're in. As for valve/guide clearance yes there are specs but I've never know an inlet valve at least to seize as long as it went freely into the guide without any drag. On that basis even a fraction of thou would seem to suffice for inlet valves. Exhaust valves get hotter and expand more but are generally made a thou smaller on the stem than inlets to allow for this. I used to ream guides until an inlet valve went in cleanly and then it would be ample for exhaust valves too. Even though most specs call for a minimum of 1 thou inlet valve clearance I'm sure I did many heads much tighter than that and never had an issue.Peter
Guide reaming was always a tedious pita. Taylor and Jones adjustables did the job well enough as long as the blades were sharp. Fixed reamers were never much fun to use by hand as they only really cut on the front bevel and ideally need a machine to drive them slowly down. I think those tiny hones are probably the easiest way and you can just spin them up with a drill but I never invested in those for cost reasons although I used them at other people's establishments. T&J adjustables only go down to 1/4" though which was fine in the old days of 8mm and bigger valve stems but not much use for modern stuff and motorbike engines with 6mm or smaller stems. I had to buy fixed reamers for those.
As a general engineering principle it's much easier to make the o/d of something to an exact size than the i/d of something. Both machining and measuring i/ds is orders of magnitude more difficult than measuring and machining o/ds. Valve seat insert bores were my nightmare. With my rickety old milling machine and hand made tooling it was never possible to machine a seat insert bore to exactly suit a stock insert. At least not to my exacting standards of interference fit. I used to machine the bores, measure each one and then turn the inserts down to the required fit on the lathe. I could cut out 8 insert bores on a bv head with the same cutter and still find a thou or more difference in size from one to another. Tiny amounts of play between the cutter and its pilot, runout in the milling machine head, differences in the amount of lubricant used would always confound my attempts to get tolerances closer than that. I used to buy inserts 1mm bigger on the o/d than I really needed and then use the excess to turn them down with carbide tooling in the lathe after boring the insert holes in the head. Horribly time consuming but at least it meant I got every fit just as I wanted it.
ukkid35 said:
Thanks again for all your contributions to this thread
It's possible that my description of the valve guide problem wasn't so clear
Hopefully these two pics show how bad the head distortion is
This is the intake rather than exhaust
Has a valve guide come loose? If so which one?It's possible that my description of the valve guide problem wasn't so clear
Hopefully these two pics show how bad the head distortion is
This is the intake rather than exhaust
Yikes. I've never seen anything that bad before. I'm wondering if the head material has been weakened to the point where it's scrap now. If a guide bore is that bad I wouldn't be very sanguine about the valve seat inserts either. There's no easy way to check those either. You can only really machine them out and start from scratch. You might be better off getting another head.
Oh I see, bloody hell! Flicking through those reminds of a bloke on Eurotrash 
Pic of guides here:
https://tvr-parts.com/tvr-parts/part-details/tvr-e...
No sizes sorry.
Pic of guides here:
https://tvr-parts.com/tvr-parts/part-details/tvr-e...
No sizes sorry.
Mignon said:
The chamber doesn't look too badly detonated. That guide play is very strange. It needs an expert examination first to try and determine what has happened. Keep us posted please.
Those pics were taken immediately after the head skim three years ago, it looked worse beforeI imagine the guide was already loose by then, I didn't remove valves to check
227bhp said:
Why have you taken it off again? To clean the swarf out?
I'd like to understand that too - so it will become the subject of a separate threadhttps://www.pistonheads.com/gassing/topic.asp?h=0&...
Edited by ukkid35 on Friday 9th March 14:09
PeterBurgess said:
How do you measure the valve stem clearance? I am intrigued as we spend a small fortune on fixed reamers, adjustable reamers and adjustable hones for correct guide clearance. Our Mira system uses pilots which rotate in the guide so we have pilots to suit each application. Our Peg system and SP Nuway system uses expanding pilots so as long as the valve gores in it seems like clearance is adequate. However, we use the Mira pilots as go no go gauges to ensure correct guide ID. Occasionally we find sintered guides which do not need reaming on fitment but very rarely!
I have seen ensuing overheating caused by det damage to pistons and ring lands and rings cause ex valves and inlet valves to seize in guide and then come loose. We have also seen many guides come loose as they have been made with bu**er all interference fit so the guides didn't have to be reamed after fitting! We use both a press to fit guides and a trusty hammer and drift (especially with horribly angled guides in heads), Keith has been doing this for 22 years since he has been with us though!
Peter
Pic of some of the more interesting valve guide tools below; adjustable diamond hone, TC reamer and the home made doodaa is what I use to press guides into some DOHC heads. The outer sleeve sits into the bucket follower and the inner runs through it like a piston driven by the press, I guess you could hammer it too. It's a very precise fit so the guides press in lovely and straight with practically no distortion, what there is is so slight a brush hone takes it out and leaves a good oil retaining surface finish.I have seen ensuing overheating caused by det damage to pistons and ring lands and rings cause ex valves and inlet valves to seize in guide and then come loose. We have also seen many guides come loose as they have been made with bu**er all interference fit so the guides didn't have to be reamed after fitting! We use both a press to fit guides and a trusty hammer and drift (especially with horribly angled guides in heads), Keith has been doing this for 22 years since he has been with us though!
Peter
Not much to say about the hone, good piece of kit, precise, pricey, but long lasting due to the diamond. The insert covers 1mm, so one will do say 5 and 6mm valve stems.
TC reamer is just the longest I could find for sensible money, you can get very long ones for a very precise job, but the price was obscene - something like £200 so I figured getting guides in without distortion was the way forward. I have my own made from Trojan for the top end jobs. Maybe because I work with more modern European and Japanese stuff it's more accurate? I dunno, but 99% of the time they fit fine. I can only remember one in the last two years when I was putting guides in and one practically fell out the other side, I reckon it had been done like that in the factory (Italy, 1980s) and I had to find a bigger guide and turn it down to fit.
A lot of stuff is done by feel, you know when a guide is too loose or too tight, but if I need to measure I use either a pin gauge or telescopic ball hole gauge.
I use a Peg grinder too, it's slow, but the seats are perfect. I made up a tool which goes into the follower hole again and takes a dial gauge so I can get all the seat depths the same.
We have the same make diamond hone we use ours for around 7.94 mm for TR guides, they have a varying requirement 7.92/3/4 mm depending on valve. We also bought carbide reamers at 7.92, 7.93 and 7.94 mm from the following company, exceptionally good prices for carbide we feel and available in 0.01 mm increments!
http://totoolsupplies.co.uk/straight-shank-carbide...
Peter
http://totoolsupplies.co.uk/straight-shank-carbide...
Peter
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