PDA

View Full Version : *HOW TO* Modify a 1.4SR head



CP
15-07-02, 01:46 PM
WARNING:
Modifying an engine head to improve an engine's performance is largely about improving gas flow though it. The ONLY sure way to discover how any smoothing or enlarging of the inlet and outlet ports (known as porting and flowing) will affect this is to undertake a series of gas flow bench tests. This requires time, knowledge and resources beyond most of us, so it is VITAL that you seek advice from professional tuners who are familiar with your engine. It is a real art and just polishing the ports up without any knowledge may actually reduce performance!! Failure to take advice from those who really know may lead to disappointing results or even a ruined head.
YOU HAVE BEEN WARNED!
A copy of a Haynes manual is recommended for anyone not familiar with this engine. They are acknowledged as the best manuals and their step by step approach cannot be bettered. Most of the information needed on the basics of removing and fitting the head is found in the manual. The following information covers difficult areas and how to go about tuning the head successfully.

THE CAR:
The project vehicle was a '91 Nova 1.4 SR with 86,000 miles on the clock.

BACKGROUND DETAILS:
The car had been bought in standard trim except for a K&N filter and Magnex back exhaust box. After some time and the engine not running well it was discovered that the cam lobes on No. 4 cylinder were badly worn and the valve stem oil seals were knackered causing the car to use a fair bit of oil. Changing these presented an ideal opportunity for some modding.

OUR TUNING CHOICES:
We took advice from veteran GM tuner, Bill Blydenstein (01763 272866) and opted for his "B" Pack modifications to our head. He has tuned GM engines for years and what he doesn't know about these engines isn't worth knowing. The work entails boring the inlet valves out to accept a 35mm valve. The inlet valves themselves are waisted and cut back around the neck. New inlet valve guides are installed and both inlet and outlet ports are ported and flowed with care taken not to break through into the water gallery casting that protrudes near the inlet valve throats on one side. Further, smaller improvements can be made by enlarging the exhaust valves a couple of mm. We chose not to bother, although we did have the exhaust valves waisted and cut back. The head is lightly skimmed to ensure good sealing around the head gasket.
Raising the compression ratio by taking more off the head was not considered for this project. To compliment these changes a Jetex exhaust system was attached to the existing 4 into 2 manifold and a Piper fast road cam was installed. With this package we were hoping for around a 15% improvement in power output taking our 14NV engine from 72 bhp to well over 80 bhp. NB there is a C14 NZ engine rated at 60 bhp and a C14 SE engine rated at 82 bhp. If your engine has not been in the best of health i.e. worn cam lobes etc. changes in the tune of the engine will be even more noticeable.

HOW MUCH?
The budget was set at around ?750. Much above this figure and it maybe better value for money to replace the engine with a larger one if your insurance can handle it!

HOW LONG?
Dismantle, inspect & clean. A weekend.
Re-assemble and get going and thoroughly check over. Another weekend.
Head work. About a week in all if your own is sent away to be worked on.
Other parts. From a few hours to within the week unless something needs importing from abroad.

TOP TIPS BEFORE YOU START:
1. Get the Haynes manual and read up on what's involved to check that you have the resources to strip the engine and get the head out and replace it OK. Note that the 1.4 has a separate section (13) covering deviations from the 1.0 & 1.2l engines
2. Get help. Take advice from professional engineers/tuners who are familiar with your engine. DO NOT rely on pub talk from your mates!!!
3. Aim for a package of components that are known to work well together and don't go for thrash mental mods unless you're prepared for lots of problems.

WHAT YOU WILL NEED:
The Haynes manual
A well stocked toolkit (metric)
Small Torque wrench
Special Tool for water pump(optional)
Special cam cover stud tool
Stilsons or similar
Axle stands or ramps
Clean Paraffin for cleaning down
"G" clamp or similar ( for the flywheel)
Valve extractor tool
Stud extractor tool
Air line if possible
Complete head seal/gasket set, new cam belt, engine oil filter, gasket sealer, sump gasket.
Silicone water pump grease, clean oil and/or cam lube


STEP1.
Jack up the car safely onto stands/ramps to allow access under the engine. To make work on the cam belt easier, remove the drivers side front wheel and the bonnet. Then, following the step by step instructions in the Haynes manual, proceed to carefully strip down the engine making sure that all pipes and attachments etc. are carefully marked, cleaned and stored to facilitate easy re-assembly. The more careful and conscientious you are at this stage, the easier it will all go back together again.

TOP TIMING TIPS.
Sequence to follow BEFORE removing the cam belt to ensure that the engine can be easily re-timed
again(1.4 Engine):
Make sure you mark with scratch marks the exact position of the distributor body against the cam housing.
Before attempting removal of the cam belt, remove the top part of the outer cam cover and align the cam sprocket mark to the TDC mark (notch at the top of cam belt cover back plate) for No.1 cylinder. Check to see which lead & cylinder the rotor arm in the distributor cap is pointing at to ensure this is TDC for No.1 cylinder.
Remove the flywheel and clutch covers under the engine & place a clamp on the flywheel so it is positioned tight up against the engine block on the front side. This will mean that when you attempt to undo the crank pulley nut you will be pulling against the clamp holding the crank in place.
Remove the alternator belt, the pulley off the crankshaft and the remaining parts of the cam belt outer cover.
Next remove the cam belt itself by pulling it off the cam sprocket using a pair of pliers - it will be replaced so it doesn't matter if it's damaged! This makes removal of other items easier.
Then, remove the plastic cam belt cover back plate from the engine block along with the alternator and its mounting. This will allow much better access to the water pump which can be a real pig to turn. This must be serviced (removed and new seal and grease installed) so that it turns freely to allow proper adjustment of the new cam belt when it's installed without leaking. Note that you will need a special tool to remove the cam belt back cover and yes, car manufacturers do use these fixings just to be bastards!

STEP 2.
Once the head is off take stock of the situation. The cylinder bores should be checked for wear and damage.
Get an experienced mechanic/engineer to have a look. To check properly the bores need to be measured accurately with a micrometer. Excessive wear will mean that tuning is inappropriate unless the bottom end of the engine has had a complete overhaul which will involve having the cylinders bored out and new oversized rings/pistons installed. A bottom end re-build etc. is pricey and the cost of this may force you to consider a complete larger engine transplant instead.
KEEP THE BORES CLEAN. FILL THEM WITH CLEAN RAG AND DON'T LET ANY DEBRIS GET DOWN THE SIDES OF THE PISTONS ONTO THE RINGS! YOU MUST BE METICULOUS OTHERWISE SERIOUS SCORING OF THE BORES WILL OCCUR.
If everything is OK you can then decide on what mods you want. Consult the experts and get the head modified if you are looking for any significant increase in power. The best gains will be achieved from heads that have larger inlet and outlet valves installed as well as flowing and porting. The aim of this work is to increase the airflow through the engine by removing casting roughness and increasing the port/valve diameters and shape. This is a specialist skill to get good results. Select a cam to suit remembering that money spent on the head and cam will be wasted to a large degree if you don't fit a free flow exhaust system. Cams can have different profiles but performance ones have higher lift characteristics that force the valves to open further increasing airflow. However, beware of "wild " (very high lift) cams which can make ordinary driving tiresome as the engine may run like shit until its in a high narrow rev band making the car really only suitable only for competition use. If the gains from theses mods are not enough, you could consider adding twin 40 carbs.
Note that a free flow exhaust is one that has an increased diameter and is designed to have good flow characteristics from one end to the other. It is important that the manifold is at least of a 4:2:1 design to reduce back pressure limiting the flow of exhaust gas out of each cylinder. Fortunately the stock manifold is of this design and has reasonably good flow characteristics.

STEP 3.
When your head has returned, screw the inlet and exhaust manifold studs back in and temporarily mate the 2 manifolds to the head to check that the port joints are smooth and matched up. If not, carefully file them so that they do. Take plenty of time to get this right and check the gaskets as well otherwise some gains from flowing the head maybe lost. Be careful not to "polish" any of the ports on the inlet side otherwise lack of swirl may allow fuel to drop out of suspension from the air/fuel mixture coming in from the carb. Leave a rough-filed finish.
Re-assemble the valves into the head having first lapped them into their seats if not already done so by the tuner. Get help here from an experienced mechanic. Make sure that the valves are kept numbered and don't mix them up.
Clean everything thoroughly and blow down with compressed air.
Re-assemble all components following the Haynes manual. If you buy a performance Cam, read the
installation literature carefully - its very important to get this right.
Drain the engine oil and remove the sump pan and oil pickup pipe and clean thoroughly. The pickup is often considerably clogged reducing the oil flow around the engine and in particular to the cam.
TOP TIP:
Connect up the fuel pump to its pipe work before bolting it into the cam cover. Then by pressing the plunger, fuel can be pumped up into the float chamber before attempting to start. This will help to get the engine to fire up quickly. By the same token turn the engine over by hand before attempting the first start to help prime up the oil system.

STEP 4.
Once the engine is satisfactorily back together double check that the cam belt timing is correct. This part of the manual is quite confusing as it alternates between the 1.2 and the 1.4. Basically there is a dot on the bottom cam pulley which lines up with a mark on the bottom of the cam cover back plate for TDC of the crank shaft. There is a white mark on the top cam shaft sprocket which lines up with a notch on the top of the cam cover back plate for the correct position of the cam for TDC. Bearing in mind that the belt must be tight on the long straight side nearest the front of the engine, turn the cam shaft half a tooth clockwise to allow the belt to be put on easily. When the cam shaft is lined back up with the notch, the cam belt should
have become drum tight on the front side and you can now tension up the water pump so that the cam belt tensioner pointer is aligned between its 2 marks. This may take 1 or 2 attempts since doing up the allen key studs holding the water pump in place to lock the adjustment in, tends to tighten the belt a bit more. Note that when the engine is turned over of has been turned off after running it appears that the cambelt is gone loose at the front side and the tensioner is tensioned too much. Don't worry this is just the effect of a little overun of the cam - when the engine is actually running everything will be OK.
Just before you are ready to start the engine, liberally lubricate the camshaft with the rocker cover off. It is vital that it gets full lubrication and quickly upon start up, if its life is not to be drastically reduced. Replace the rocker cover and then start and run the engine evenly and quickly up to 2500 rpm. This should be maintained for around 20 minutes so that the followers are bedded onto the cam properly. Have some else do this so that you can monitor the situation under the bonnet. Don't forget to make sure the oil light goes out and keep an eye on the water temperature guage!! Don't be too alarmed by smoke - the new exhaust will burn its paint off for sometime. Don't let the engine idle if you have to turn off for some reason.
After the initial run in time turn off and check over thoroughly.

STEP 5.
If all is OK you are now ready for the road. Drive the car normally but in a restrained manner for the first 500 miles and try to avoid numerous short trips. Prolonged hard work straight off i.e flat out up the motorway will cause the valves & seats to be damaged by overheating before adequate coking ( the knaki coloured deposits that cover the valves and sparkplugs etc) occurs. The engine might not run evenly with dead spots etc to start off with but as the miles roll by, coking will improve these problems and make the engine more efficient and more powerful. So long as the car runs OK it is not be advisable to go straight to a rolling road. However, if it runs very badly, get on one to help with fault diagnosis. When the car has covered around 3 - 5000 miles it can be taken to the rolling road for a final set-up and to get it dyno'd since by then acceptable amounts of coking will have occurred. They will see to any necessary re-jetting of the
carb and set the timing up properly. The best bit, however, will be a graph showing the power curve and what you will now have at your disposal at the wheels!

TOP TIPS:
Only run your modified engine on super unleaded high octane fuel to prevent pinking.
Changing the oil ( not the filter) very regularly i.e 6 or so times a year is recommended as it can "blueprint" the engine naturally and prolong its life enormously.
Use rainwater or soft water to prevent scaling and overheating in the heating system.
Uprate your brakes and suspension.


That's about it.

What happened to the project car?
Well it went very well & enjoyed itself giving all and sundry a good rinsing until it was parked in a wall - the brakes had not been uprated - before it had been rolling roaded!! Therefore unfortunately there are no BHP figures.

What happened next? Well it needed a new bumper etc and a head light. Rust in the wings was starting to be a problem so we replaced the wings, added a spoiler kit found second hand up the breakers and rubbed it all down and gave it a respray. It was treated to a set of 16" Mille Miglias put back on the road and then... the head gasket went!

To find out what happened next, watch out for "How to put a 1.6GSI engine in your 1.4 SR and add Twin 40's to it".

Charles Paynter: charles.paynter@farmline.com

Disclaimer:
All the information in this article is expressed as the personal opinion of the author and in no way will any liability be accepted for any loss or damage however caused as a result of following the advice given herein.