Please visit the Club's website https://www.dloc.org.uk/ to join. Visit https://www.dloc.org.uk/adhoc to DONATE towards the cost of the forum.
Please don't post someone's email address to avoid it being harvested by spambots and it's against GDPR regulations.
Always look at "ACTIVE TOPICS" to see all posts in date & time order as they are sometimes moved; or look at "Your Posts".
Please add Reg. nrs. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.
CHANGED YOUR EMAIL ADDRESS since registering?, click your username and check your address in User Control Panel, Profile, Account Settings.
If you want help to register, use "contact us" at page bottom for help.

DB18/2 low compression

Mark Bullen
Posts: 219
Joined: Mon Feb 15, 2016 1:07 pm
Location: Wiltshire

DB18/2 low compression

Post by Mark Bullen »

I have very low compression (25psi vs (100 to 120psi)) on 2 cylinders (3 and 4). Thus its time to take the head off and investigate.
Hopefully, because i don't have any sign of the dreaded mayonnaise and that the low cylinders are next to each other, it might be that i am lucky and have a leak across the bores rather than major ring failure (but who knows until the head is off or a try a wet compression test, either way its a head off job.

My request to the forum
1. do you undo the bolts (gradually) in the reverse of the tightening sequence (as per the manual)?

2. does anyone have a recommendation of someone who could check/repair/rework the head local(ish) to Wiltshire. I am aware that Beales Engineering and or J&E Engineering both have a good reputation for this work but its a long drive and the thought of shipping the head is a bit daunting.

3. the engine hasn't noticeably burnt oil but if the head needs work, then now could be the time for new guides and potentially inlet oil seals, exhaust valve seats for unleaded fuel. any budget quotes people could share for work they have had done.

4. if the head is off and then i flush the block and replace core plugs then it makes sense to clean out the sump etc. can you remove the sump with the block in-place? i tried and failed before but it might be lack of knowledge

5. any other suggestions of what i should look out for?

Thanks in advance

Mark

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: DB18/2 low compression

Post by Brian-H »

In answer to sump removal - in the late 70s I was informed that it's possible to check piston rings with the engine in situ, by removing the head and the sump (and then undoing the conrod bearing and sliding the piston up for inspection at the top) - but that's on a Consort (and in fact I ended up taking the entire engine/gearbox out for other reasons)

Db n j
Wise Man
Wise Man
Posts: 919
Joined: Sun Mar 13, 2016 8:55 am
Location: uk shropshire

Re: DB18/2 low compression

Post by Db n j »

Mark,

No advice on a good machine shop in your area - maybe BigAl can help ?

Wondered if it’s best to see what the head gasket looks like when you remove the head.

For example, if the oil consumption / smoke was very low, maybe a decoke and new head gasket is enough ?

For insurance getting the head checked for flatness might be useful.

Other stuff like valve guides / seats maybe not really needed - as you say not much smoke from the exhaust. Dont forget that the engine was designed for ww2 applications - petrol quality does not appear to cause these engines undue wear problems.

On the other hand, removing the core- plugs and rodding the water jacket from above will be very helpful in reducing overheating.

Not sure I’d recommend removing the sump if it is relatively leak free - I have done this twice on my empress to try to reduce oil escape. Can be done for that model by removing 2 track- rod ends which allows the front of the sump to be manoeuvred out. No need to remove engine mounts or raise the engine.

Only my thoughts, but maybe one step at a time ?

Stan Thomas
Wise Man
Wise Man
Posts: 795
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: DB18/2 low compression

Post by Stan Thomas »

Hi Mark,

Your head gasket has blown between cylinders 3 and 4 - which is not uncommon.

To answer your questions:

1) No need to undo the head nuts gradually.

2) It is probably uneccessary to have the head attended to, as you have a cast iron head which rarely warp.

3) If its not burning oil, just renew the inlet valve stem seals. No need to have hardened seats fitted.

4) You could remove the core plugs to flush the block - but there are good flushing products on the market. Use one before you dismantle to do the head gasket. More importantly, flush the radiator. ('ears agoo, when I werked on Daimlers in Bermingham, if yow ad a new ingin fitted, thayed fit ya a reconditioned radiator as well as it was considered part of the job).

Use a good quality flushing oil - no need to remove the sump (i.e. the base chamber - Daimlers do not have sumps).

With the head off, remove the cylinder head studs and with some 100 grit "wet-and-dry" wrapped round a large flat file and plenty of parrafin clean the block surface. Likewise the cylinder head. If you are refitting with a copper-composite gasket, coat it liberally with oil. If it is a stand-proud shim type, fit it bone dry. But you must be scrupulously clean. While you have the rockers off - check they are not "indented" by wear which gives a false tappet clearance - but they are easily ground back to shape.

Torque the head nuts in correct order to 30lbs/ft and leave for 30 minutes whilst you listen to Frankie Laine records. Then finally torque down in one go - not in small increments. To do the job properly, re-torque the head after about 500 miles, especially if you have used a copper-composite gasket.

If the head does need planning consider removing 0.100" (100 "thou") to increase the compression for modern higher octane fuel - but you will need to make packers of the same thickness to fit inder the rocker pedestals to retain the correct operating angle for the rockers.

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: DB18/2 low compression

Post by Brian-H »

Stan Thomas wrote: Tue Apr 27, 2021 9:14 am ......renew the inlet valve stem seals.

......there are good flushing products on the market.
I'm seriously thinking of (for the sake of simplicity) putting the head back on and getting the (replacement) engine in my grandfather's car Consort going.

How are the valve stem seals renewed ?

Got any examples of good flushing products ?

Stan Thomas
Wise Man
Wise Man
Posts: 795
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: DB18/2 low compression

Post by Stan Thomas »

Ill look up some detail on flushing products when I get a moment - but the inlet valve seals - irrespective of whether or not they were fitted originally are just a plain rubber ring which fits over the valve stem to break the air-stream of the induction stroke sucking oil which has collected in the spring collet down the valve guide.

Any motor factor would sell something adaptable - or you could use a tight-fitting "O" ring. Just push it right down over the valve stem upon assembly, and when the valve opens in operation it will be automatically pushed back up the stem to the correct position.

John Hitchins
Site Admin
Posts: 244
Joined: Mon Feb 08, 2016 10:52 am
Location: Wellington Somerset

Re: DB18/2 low compression

Post by John Hitchins »

I had stuck valves slightly open, presume you have checked yours are closing?
Really annoying as has happened twice now.

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: DB18/2 low compression

Post by Brian-H »

Stan Thomas wrote: Tue Apr 27, 2021 10:28 am Ill look up some detail on flushing products when I get a moment - but the inlet valve seals - irrespective of whether or not they were fitted originally are just a plain rubber ring which fits over the valve stem to break the air-stream of the induction stroke sucking oil which has collected in the spring collet down the valve guide.

Any motor factor would sell something adaptable - or you could use a tight-fitting "O" ring. Just push it right down over the valve stem upon assembly, and when the valve opens in operation it will be automatically pushed back up the stem to the correct position.
I believe that someone non-Daimler may have told me something similar about 30 years ago, and I've totally forgotten :oops: (I think they may have said to use some kind of "orange goo" though, not actual rings)

Db n j
Wise Man
Wise Man
Posts: 919
Joined: Sun Mar 13, 2016 8:55 am
Location: uk shropshire

Re: DB18/2 low compression

Post by Db n j »

Just a couple of points.

I read Kevin Bennett’s website article about block cleaning, and the sediment that collects in the block, especially at the back of the Db18 engine as it slopes down.

For the Barker I removed the core plugs and the drain tap. I fixed a piece of brake pipe with the end shaped like a quill to the end of a hose, and worked the sediment from the top of the block. Took hours to dig (most) of it out, and get clear water running out.

I am happy to recommend this method to you, knowing that you can feel the jacket is clean.

Second point is about sticking valves. Just worth checking the cam followers. They can stick in their bores and give a similar result. It has been known for people to destroy the buckets trying to get them out. Worth a check (especially if you are removing the head anyway.)

JT7196
Extremely Wise Man
Extremely Wise Man
Posts: 1535
Joined: Sat Feb 13, 2016 7:22 am

Re: DB18/2 low compression

Post by JT7196 »

Hi , if you plan to have your engine reconditioned , contact Cox & Turner as I did last year.
They will chemically clean your engine and I can assure you the result has been amazing, with the engine temperature staying almost too low now.
Up until till this time , I had a mechanical fan fitted, and this was also supplemented with and additional electric one,
now it would seem that I probably do not actually need either !!
Cox & Turner,
Huish Farm,
Yeovil Road,
Tintinhull,
Yeovil,BA22-8 QL
Tel :- 01935-826816

Cheers Al 👍👍😊😊

Post Reply