2.4T Engine rebuild advice

[914Chap]

Hi,

I am looking for advice on how far I should go with the engine rebuild of my 2.4T. I have removed the engine from my RHD 914 as it was not running correctly along with the common signs of smoking. The engine had stood for some years while I completed the conversion of my 914 to RHD and 6 cylinder etc. and was bought as an unknown quantity. However, I chose to install it and see how it went as I needed to prove that everything else worked, and indeed it did drive under it's own power for the first time in years!! The engine started almost first time and appears to make the expected oil pressure with no untoward noises.
The problems with the engine became apparent while I was setting up the Weber carbs and I found that I was not getting any response while adjusting number 6. Cylinders 1 to 5 responded as expected, but number 6 refused to respond to adjustment, with some spitting back through the choke. Also, the plug on number 6 showed no signs of firing. Swapping the plug which was sparking, made no difference. After numerous attempt I finally gave up and conducted a compression test. Cylinders 1 to 5 gave readings of approx 75 psi and were fairly consistent. However, as suspected number 6 gave 0 psi, absolutely nothing! So no surprise really that it was not responding to adjustment. I had already adjusted the valve clearances and adjusted the timing prior to rebuilding the carbs with the correct jets chokes, emulsions etc.
Thus far I have removed the top end cylinders and barrels. None of the head gaskets appeared to be damaged or the sealing face of the heads. Firstly, I poured some paraffin into the head chambers and found that all appeared to hold fluid for some time, over 12 hours. I then removed cylinder head number 6 to inspect the valves. The exhaust valve did not appear to be damaged, however when I removed the inlet valve I could see that only about 50% of the valve seat was seating correctly. The other half clearly showing signs that it was contaminated and not sealing. I am unsure at to why it was not sealing as the valve does not appear to be bent from my crude attempts to check.
Clearly, I need to have the heads rebuilt, with new guides, seats and valves checked and re-cut etc. Does anyone know how reliable the K line inserts are or am I better having the original guides replaced? There appears to be more play in the valve guide on the inlet than the exhaust which I was surprised by. My question is how far do I need to go? I plan to remove the crank and rods to inspect them.
But my main question is, are there any other mods I need to do while it is all apart? I have so far measured the pistons and they are in tolerance as are the barrels, for both wear and ovality. I have not yet measured the piston rings or grooves. However, this engine only has a 7.5 to 1 compression ratio. I believe I can have the cylinders re-bored and use Wossner pistons which would take it up to 10.5 to 1. Is this worth doing without other significant changes, cams etc.? also, is it as straightforward as it seems? I have already updated to hydraulic tensioner's and fitted Turbo valve covers and I plan to modify the air deflectors. Is it necessary on this type of engine to replace the head studs or fit time-serts into the cases?
Sorry for the number of questions but I am unsure just how far I need to go in order to get the engine to be reliable.
Any advice or suggestions would be much appreciated.
Thanks Jonathan.

[Gary71]

I’m no expert, but I have (successfully so far!) rebuilt my 2.4T engine a few years back.

Q: I am unsure at to why it was not sealing as the valve does not appear to be bent from my crude attempts to check.

A: Probably contamination from carbon or something going down the port. If there’s any doubt on the straightness of the valves or measurable wear then replace them. Mine were all under spec at some point over the length.
I also replaced all the springs and caps. Not sure I really needed to do the springs, but on very close inspection the caps had little cracks in and once you’ve seen that they need to go.

Q: Clearly, I need to have the heads rebuilt, with new guides, seats and valves checked and re-cut etc. Does anyone know how reliable the K line inserts are or am I better having the original guides replaced? There appears to be more play in the valve guide on the inlet than the exhaust which I was surprised by.

A: I’ve not used the K Line inserts but had the guides replaced/honed etc to match new valves. I also had the seats recut and the head sealing faces flycut. Also fit inserts in the exhaust/inlet stud holes if they are not perfect.

Q: My question is how far do I need to go? I plan to remove the crank and rods to inspect them.

A: Glad to hear you are splitting the case. I wasn’t going to as I had no signs that required it. But when I summoned the courage to do the job properly I found worn bearings so really glad I did!
Get new endless chains for rebuild time. I have a (homemade) set of chain supports you can borrow for holding it all when you put the case back together.
I had new small end bearings fitted and the rods balanced.

Q: But my main question is, are there any other mods I need to do while it is all apart? However, this engine only has a 7.5 to 1 compression ratio. I believe I can have the cylinders re-bored and use Wossner pistons which would take it up to 10.5 to 1.

A: This is just the start of the slippery slope
I looked into all this and eventually put the original cylinders and pistons back together with new rings. Several reasons for me:

Budget: It had already run out and pistons and cylinders were in good condition.

I have the correct size grape hone if you want to give the bores a quick clean up.
I also have an ARP piston ring compressor in the right size which is a tapered aluminium ring that makes it SO easy to get the pistons back in without risking the rings.

Do I really need it: I have a fast daily so did I really need more power in the toy?

Slippery slope: Yes you can do a piston swap (also 2.2S pistons can be used for a good CR bump) but then probably you’ll want E or S cams to really make the most of it, then you’ll realise the port sizes are bigger, and the carbs will need rejetting... and is your oil cooling up to it...

Q: Is it necessary on this type of engine to replace the head studs or fit time-serts into the cases?

A: if they aren’t showing any issues then leave them in place. I replaced one as I managed to bend it when I dropped the case half

[Mike911scrs]

HI Jonathan

the head studs should be OK

I take it the engine has cast-iron cylinders, if you go to-far on the O/S you may run into over heating prob's, as there is no piston jets in the crank cases, some con-rod mods can help over come this

if you are making the engine bigger and lifting the C/R, you will need to open up the intake ports/manifold and look at some better cam's or re-grind on your cams (if usable)

regards mike

[Gary71]

Hi Mike, My 2.4T case has oil squirter jets. Thought they were standard for the 2.4 onwards?

[914Chap]

Thanks Gary and Mike,
Your advice is much appreciated. I am leaning towards sticking with the original barrels and pistons if everything checks out. It doesn't seem to be an option or make sense to just increase the compression ratio without all the other mods required and I'm not sure where I will then end up. Also, I have only just rebuilt the carbs with the correct jets etc. for the standard spec engine. Hopefully if I stick with what I have I may also get this back together sooner rather than later. I would rather have the car on the road after so long, than try and search for more power before I have even used it.

Gary, thanks very much for the offer of the loan of the cam chain holders and the ring compressor. I will send you a separate PM about those. Your experience has convinced me that I should open up the crankcases. I was interested to see your comment about the valve caps being cracked, I had never even thought to check these, where about on the cap did you find the cracks?

I have also seen a number of previous engine builds where people have installed a later oil pump. My engine currently appears to have good oil pressure, can I assume that the pump I have is OK? I am unsure as to what the later pump would improve?
Cheers Jonathan.

[Gary71]

Replied to your pm

Don’t know much about the oil pump to be honest, mine looked ok so went back in! Unlimited budget may have seen it replaced.

[abzadams]

My engine build is here (toward the bottom of the page). It may help with some decisions:
https://www.ddk-online.com/phpBB2/viewt ... n&start=45

[911hillclimber]

Don't be put off re-building the engine DIY.
The Dempsey book is well worth the money, well laid out and explains all the details.

Gary knows a good machinist (for the head valve guides etc), or, you won't go far wrong using Mike above at MB Engineering who did my valves where a pro Big Name Porsche engine rebuilder failed.

A stock T engine is a nice road engine.

[914Chap]

Thanks chaps for all the help and suggestions. I will take a look at the thread Rich as you suggest, thanks.

I have a copy of the Dempsey book which as you say is very helpful, along with Bruce Anderson's Performance Handbook they cover most things but it is always good to hear how others have done things and who they used for machining etc. I plan to stick with the stock setup as I believe it will be enough for my 914 and I really have no desire to get carried away,it is only a road car after all.

I have done a rebuild on a 2.4 before but it was 25 years ago and some things do seem to change such as the K line valve guides which were not available then I don't think. There seems to be so much more that people do to these engines these days, or maybe it's just easier to read about what can be done now. Also, my previous engine rebuild had no significant faults at the time other than the obvious wear to the valve guides. Hopefully, a good rebuild of my heads this time will also sort the problems I currently have with number 6 cylinder.

Thanks to everyone for their contributions and help.
Jonathan.

[jonat127]

The other mods I did on my engine were the oil bypass mod and the oil pump upgrade. Both in the Dempsey book.
One other thing I learned from experience was the camshaft oil squirter lines can easily get blocked.
Whilst you have the cam carriers off give these a good wash and blow through and ensure all squirter holes are open.