SNG Tappet Hold Down Kit

gmunro · Post by **gmunro** » Mon May 30, 2016 11:52 am

Hi Gents and Ladies. I have just bought a XK 4.2 tappet hold down kit from SNG. I note that they do not lie flush on the head casting and when fitted, will sit a few mm above the casting. Is this correct or are my tappet guides too high?

Also, if anybody else has done this conversion, can you advise what drill size and tap should be used? Any other tips would be gratefully received.

Many thanks,

George

jagwheels · Post by **jagwheels** » Mon May 30, 2016 6:17 pm

I to just got the SNG hold down kit and I have emailed barratts asking what size tap to use. They say not to use a tap and just a 3.9 drill bit. But I have not fitted them yet,
Regards John

gmunro · Post by **gmunro** » Mon May 30, 2016 6:39 pm

HI John,

Many thanks for your reply. Does your hold down kit also not lie flush with the casting?

jagwheels · Post by **jagwheels** » Mon May 30, 2016 7:08 pm

Yes I think so

rswift · Post by **rswift** » Mon May 30, 2016 7:56 pm

I had this done to my car earlier in the year....I was going to do it myself but wimped out !

I used the services of an experience XK engine builder, who luckily happens to be local to me.

I believe the guide does sit a little proud of the head, and also that he drilled straight into the head.

My kit was from David Manners, but assume it's same/similar part. I had a guide which was already loose, it's worked a treat, and given me peace of mind.

gmunro · Post by **gmunro** » Mon May 30, 2016 8:28 pm

Brilliant guys and many thanks. I have just had my head done and am looking for "belt and braces" reassurance going forward. Seems that this kit is the way to go.

abowie · Post by **abowie** » Mon May 30, 2016 9:17 pm

What is important is that the milled out section sits flat and evenly against the edge of the tappet guide.

I would strongly advise tapping the holes despite the advice you have been given to the contrary. If you don't the fastener will deform the head material and in turn compress the tappet guide. The clearance of newly machined guides is under .001" and they can jam.

I base this on experience; I have fitted these to at least 6 heads in the last 2 years. The first couple of kits I used had self tapping screws. I found that with the hold down plates fitted I was unable to remove and replace the buckets while shimming the valves. The kits we use now come with threaded Allen headed setscrews.

Otherwise this is not a difficult job although drilling a hole in the head for the first time is a little stressful.

jagwheels · Post by **jagwheels** » Mon May 30, 2016 9:47 pm

I'm just saying what Barratts told me I have not done the job yet.
Simon Cottrill from Barretts said the screws are Taptite Screws.

64etype · Post by **64etype** » Tue May 31, 2016 12:58 am

I had to grind the hell out of them (particularly the ones on the ends) to get them to fit parallel to the guide. Used the screws in the kit.

Vegard · Post by **Vegard** » Tue May 31, 2016 6:46 am

What is this kit?

Post by **mgcjag** » Tue May 31, 2016 8:11 am

Have a look here http://www.sngbarratt.com/ProductDetail ... dea2f&b=US

gmunro · Post by **gmunro** » Tue May 31, 2016 10:03 am

Once again guys, many thanks for your input. First of all abowie, your advice sounds great. Can you give me any further details of the allen screws. drill and tap to use and so forth? Are the allen screws hardened? Look forward to hearinf from you.

Vegard : When new tappet guides are fitted, they can sometimes work themselves loose. A "hold down kit" has been developed to literally hold the tappet guides in place so that should the new guides become loose, they will not come out of position and cause untold damage! The fitting of the kit is a safety net - not essential - but a good idea. Hope this helps.

abowie · Post by **abowie** » Wed Jun 01, 2016 1:56 am

I think the last couple of kits I used came from XKs in the US.

From memory the screws were probably 3/16" UNC with an Allen head. I would have to check and see if we have any kits in stock at the moment. I will be at the workshop tomorrow; I will see if we have them.

The size really isn't critical as long as it fits the hole in the hold down plate and you have the right tap for whatever you choose to use.

ralphr1780 · Post by **ralphr1780** » Wed Jun 01, 2016 8:01 am

Here is how its done on my S2 (was this way when I bought it):

And before anyone asks about the second photo: yes shim has been changed!

Vegard · Post by **Vegard** » Wed Jun 01, 2016 9:17 am

gmunro wrote:
Vegard : When new tappet guides are fitted, they can sometimes work themselves loose. A "hold down kit" has been developed to literally hold the tappet guides in place so that should the new guides become loose, they will not come out of position and cause untold damage! The fitting of the kit is a safety net - not essential - but a good idea. Hope this helps.

Excellent, thanks. Makes perfect sense.

gmunro · Post by **gmunro** » Mon Jun 06, 2016 6:38 pm

I know it is advisable to fit the hold-down kit to the exhaust side of the head but is it necessary/advisable to also fit a kit to the inlet side? Perhaps overkill?

Gfhug · Post by **Gfhug** » Mon Jun 06, 2016 8:14 pm

My loose guide is on the inlet side, so for little extra effort do both.

Andrew (abowie) are you saying that if the milled out section is only touching at one point due to not having the screws perfectly perpendicular to the plate that the guide can still rattle?

I have fitted the SNGB kits, have long skirt cam followers, later 12-14 thou cams yet still haven't cured the problem. Now my hold down kits aren't perfectly touching all along the milled section, could this be my problem?

Ralphr1780, fyi your hold down screws are different to the SNGB, XKs etc. which have a flat plate held down with two screws against two adjacent guides.

Thanks
Geoff

abowie · Post by **abowie** » Wed Jun 08, 2016 2:57 am

Gfhug wrote: Andrew (abowie) are you saying that if the milled out section is only touching at one point due to not having the screws perfectly perpendicular to the plate that the guide can still rattle?

I have fitted the SNGB kits, have long skirt cam followers, later 12-14 thou cams yet still haven't cured the problem.
Thanks
Geoff

The guides are a firm press fit with the head heated in an oven. In the 1961 Jaguar factory video it shows them being installed using a mandrel and a large hammer.

If you think that a guide is able to move so much that it is actually causing noise it needs replacing. If a guide can move it could touch the camshaft and at worse cause the bucket to jam inside it with subsequent damage to the engine.

The hold downs are only an extra line of security for guides that having been inspected are still firm in the head. Fitted properly the milled out section should be in contact with the guide all along its lenght. As mentioned above you sometimes need to relieve the hold down with a grinder to get it to fit flat. As long as the holes are reasonably straight the screws will hold it in place adequately. I tend to Loctite them as well.

WRT noise, did you have the guides machined or did you just fit new buckets? The correct clearances between bucket and guide are under one thou. While long skirt buckets are less able to rock when worn, causing noise they won't fix the problem if there is still excessive clearance. The solution is to have the guides machined to fit new oversize buckets.

We currently don't have a set in stock so I haven't been able to check the thread, but I don't think it's critical as long as they fit the holes.

Gfhug · Post by **Gfhug** » Wed Jun 08, 2016 7:18 am

Thanks Andrew

There were indications that inlet 3 guide had been loose judging by witness marks on it, but all guides are all very firm in the head and seem to be the same height above the head. When rotating the cam to check tappet clearances there is good clearance between the lobes and guides. The buckets all seem to be a snug fit, sliding in smoothly, a couple even needing easing out with a pair of grips as a magnet won't pull them fully out.

I really had thought all had been sorted by fitting the hold down kit, but will refit them making sure the milled section fits snugly and re-check the fit of the suspect buckets.

Otherwise it'll be the head off for a new set of guides, etc.

Many thanks

Geoff

Post by **mgcjag** » Wed Jun 08, 2016 7:50 am

Hi Geoff.....a friend has had a rallting in his engine...originally diagnosed as tappets...new longer ones fitted......still rattling....head off and re machined new guides and holddowns fitted...guess what...still rattling.....latest diagnosiss as small ends....so engine comming out

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