Building a 400bhp+ 2.5 ltr 944 Turbo

PSH · Jul 29, 2012

I didn't find the time to get as much done as planned this weekend but I did get one important job out of the way, replacing the rod bolts. The preferred method for doing this would be to use a suitable hydraulic press, I sold on my 40 ton press some years ago due to space and didn't fancy driving up to my son's garage to use his. The alternate method which is probably how most DIY mechanics would have to do it and therefore worth going through here is to drift the bolts out. First picture for tonight shows No.1 rod ( I tend to do things in order), you need a good vice for this. As can be seen the rod is held securely between two pieces of 3/4" plywood, I used this as it can be compressed enough so that it grips both the big end and little end thus supporting all of the rod, the little end is not as wide as the big end. Once held securely a couple of sharp taps followed by lighter ones enabled the old bolts to be removed. All four rods were done in this way.

Next job is to fit the new bolts ( Raceware of course), the rod is now held upright in the vice still sandwiched between the ply, I first placed the bolts into the rod ensuring that the spline is engaged correctly. Then using a brass drift and hammer I tapped them home, this sounds easier than it actually is, you need to use pretty heavy taps to get the bolt fully home which it must be,I don't like to rely on the bolt being pulled in alone by the torquing procedure in case you overstretch the bolt. In the picture you can see one bolt fully engaged with the second being tapped home.

Ok, so all bolts are now fitted, next we need to refit the bearing cap( without bearing shells) and torque it down to the specified setting, again there are two methods for doing this with the preferred option being the stretch method. I wouldn't like to rig up something using my dial gauges as the amount of stretch is very small and needs the correct tools to be sure you get it right. So again I am forced to use option 2, that being the traditional torque method. The torquing procedure has 3 steps, 25ft/lb,45ft/lb and finally 65ft/lb, the threads must be oiled using 40/50 oil, no other or you won't get the correct torque. This is done twice( a 3rd and final time will be when refitted to the crank) to ensure the bolts are fully home, each time make sure the threads are clean, re-oiled and re-torqued following the 3 steps mentioned.

Before we can say that the rods are ready we need to check that the big ends are still round as it's possible for these to get out of round during hard use or during new bolt fitting. I couldn't find the measurement for this in the Porsche manual, it only gives the journal sizes but I was happy to discover that all 4 rods when measured across two axis at 90 degrees to each other are identical and all four rods measure within 0.01mm of each other. This is very good news as I don't have to go back to Serdi's to get the big ends re-machined round. This is testament to just how strong these Porsche forged rods are, I doubt very much if using the later non forged rods and running for a number of years with a 75% increase in power that they would still be the same shape and therefore would require some machining to rectify the problem.

Final picture for tonight shows all four rods with their caps correctly torqued ready for fitting later, I'll leave them like this until I'm ready to re-fit the new pistons and install in the block. Note the old rod bolts alongside, I'll keep these as they are perfect for holding work down to the mill bed, as are the old wrist pins for using as parallels, again very handy for milling.

More soon Pete

PSH · Jul 30, 2012

On to fitting pistons to rods, here I've put new and old together for comparison purposes. The IASA race piston is about 1.5mm less in height, the lip at the bottom of the skirt is a lot wider and the recess cut for the wrist pin is a lot bigger as can be seen in the photo. I haven't measured the dish capacity but they look very similar in size, the other important differences are the V groove between rings 1 and 2 ( holds higher boost and stops top ring from flutter) and most important of all the size of the rings themselves. IIRC they are around 40% thinner than standard and because of this will have far less friction.

Rings fitted to piston No.1, bottom (oil) ring is fitted first followed by 2 and 1 rings. The oil ring is the most fiddly as it consists of 3 parts and the two outer rings need to fit over the lips on the centre ring, I find the easiest way is to line up the 3 gaps together and slid the rings on from the bottom, probably should do this from the top but it made more sense to me from the bottom as you have the two large recessed cut outs for the wrist pins there that allow you to easily place the rings ready before fitting into their slot. With the gaps lined up as mentioned I took hold of the middle of the ring, made sure the two outers were fitted over the centre ring lips and placed the ring into it's groove. Once you have this part in it's easy to work around each side until reaching the gap. I then positioned the two outer part gaps at 180 degrees to each other and the centre section gap at 90 degrees to them. rings 2 and 1 are a simple case of holding by the gap ends and carefully opening the ring until it clears the piston and then fit into the groove, be careful here not to twist the ring. Position the gaps on these two at 180 degrees to each other and also away from the gaps on the oil ring.

Each wrist pin was checked for fit in the rods, there was an awful lot of play here with the old bearings, Serdi have machined these perfectly and it's always very satisfying to get that sucking feeling of a perfectly engineered fit between two parts, well I find it satisfying, these rods are now ready for some serious abuse...

Now fit a clip into one side of the piston, theres a small notch here that helps with this, you don't need a tool, just slide one end of the clib into the notch and then work around with your fingers until you get to the stage in the picture, last job is to push the end into the notch again using your fingers.

Fit wrist pin into the end without the clip, place rod into the piston and push the pin home until it hits the clip, last job is to fit the other clip, I used a generous amount of assembly lube here. Something of importance to note, both the piston's and the rods have one way of fitting into the block so don't get them around the wrong way. Pistons dish is slightly offset, the larger top section of the piston faces the right hand side of the engine( drivers side for us), the rods need to be fitted so that the stamped matching numbers on the sides face to the left side of the engine. One other thing to note, the rods and there corresponding caps are numbered, these must not be mixed up and the cap number must be on the same side as the rod number, ie the cap only goes on one way. This is critical guy's so don't get it wrong. Picture shows No.1 piston fitted to it's rod and this shot shows the piston as it would be facing the front of the engine. The rods were marked when removed with a centre punch, one dot for No.1 etc etc. To be honest this may not be that critical when you consider all of the machining that's been done to the block and rods but I like to keep things in order and if this was a matter of simply refitting without any machining it's again critical that you put the right rod/piston in the right bore.

Last picture for this stage shows all 4 rods fitted to their pistons, they are laid out as if they are facing the front of the engine, note the stamped numbers on the sides of the rods.

I come to a halt again now as I need my son to bring his ring compressor home, hopefully it won't be too long of a delay. Pete edit: I forgot to mention that when fitting the top ( compression ring) make sure that the small inner edge bevel on the ring is at the top, don't fit the ring upside down or you'll encourage carbon deposits to build and thus a sticking ring.

barks944 · Jul 30, 2012

Excellent job! Great to have such an informative writeup to go with the pics too. I like the idea of the thinner rings, I read that you loose a lot of power from them, especially the oil scraper ring?

PSH · Jul 30, 2012

ORIGINAL: barks944 Excellent job! Great to have such an informative writeup to go with the pics too. I like the idea of the thinner rings, I read that you loose a lot of power from them, especially the oil scraper ring?

Thanks for the comments Thomas, yes you loose a lot of power through the cylinders, iirc the rings alone account for 40-45% of power lost through the cylinders due to friction. Of course it's a compromise as smaller rings mean higher wear, however if the rings are made from the toughest materials available today I doubt you'd notice any extra wear, things have moved on a long way in the last 26 years.. Pete

Diver944 · Jul 31, 2012

Keep up the good work Peter, I'm loving watching the progress each step of the way

PSH · Jul 31, 2012

ORIGINAL: Diver944 Keep up the good work Peter, I'm loving watching the progress each step of the way

Thanks Paul I'm trying to give as much info as possible without going to over the top, helps me keep track of what I've done and hopefully helps others understand the insides of the 944 engine, after all this engine is a learning curve for me too. Pete

PSH · Aug 2, 2012

Finally I received the crank scraper so upwards and onwards At first I feared that I would have to take the main frame off again and set the studs higher to give me more thread, them I engaged my brain and realised that Ishihara-Johnson had supplied new thinner washers to replace the originals, or in my case the thick Raceware washers. First picture is just to show the difference between the washers and that there is enough thread to torque down, btw the nuts are only hand tight in this picture.

I-J state that you need to fine tune the scraper to fit with at least 1mm clearance and to double check the end float, if too much play the thrust bearings will have to be replaced. since all my bearings are new with end float is as new I'm lucky and don't have to worry about this. The picture shows the scraper being marked with a felt pen where it needs material removed.

Next was to temporary fit a rod cap and check again for clearance, as you can see a little filing is required here too.

So it was then a case of holding the scraper in a vice and some elbow grease to remove the unwanted metal, remember to file off the burr here too.

Close up of the rear crank webs showing the scraper now has enough clearance to be fitted.

last picture shows the scraper now torqued down securely to the main bearing frame. There will be one last job here which will have to wait and that's checking clearance when fitting the sump. I-J recommends to remove any metal from the inside of the sump and to try and avoid removing anything from the scraper itself, I'll cover this part when I get to it.

Pete

TTM · Aug 2, 2012

I can't say I like the way the "2.5" label is stamped on this crank scraper. Looks like the center of the "5" could break easily and make its way to unwanted placed. I'd remove all this.

PSH · Aug 2, 2012

ORIGINAL: TTM I can't say I like the way the "2.5" label is stamped on this crank scraper. Looks like the center of the "5" could break easily and make its way to unwanted placed. I'd remove all this.

Hi Thom I can see what your saying, however it's probably not very clear in my photo but the stamped 2.5 is actually over no. 2 main bearing and thus not going to get much oil hitting it with any force. Also I-J have sensible constructed the scraper out of 1/8th steel plate which I can't see going anywhere even if it was in direct flow of the oil. Pete

George Elliott · Aug 2, 2012

Pete, thanks for the image, I have never heard of this device before let alone seen one. good that it finally got to you George

PSH · Aug 3, 2012

ORIGINAL: George Elliott Pete, thanks for the image, I have never heard of this device before let alone seen one. good that it finally got to you George

Your welcome George and yes it did get to me eventually, no more USPS services for me, it was bad enough with the service from I-J without USPS throwing their tuppence worth in...lol Pete

PSH · Aug 4, 2012

Todays update sees the pistons back into the block.. Returning to the vice, the rod is held between the two pieces of ply with the piston sitting flush on top, in this position I placed the ring compressor over the piston and tightened until the rings were all pulled into the grooves.

Once the rod was removed from the vice I held the compressor and taped the piston down a little so that the skirt was about 1/2" out from the bottom ready for sitting into the bore. The rod bolts were covered with suitable pieces of rubber hose so as not to damage the bore or the crank journals. Don't forget to fit the bearings and lubricate with assembly lube prior to fitting, also oil the ring compressor before compressing the rings so that the piston slides out easy.

With the piston slid carefully into it's bore I used a rubber mallet handle to tap the piston home. I set the crank so that it was at BDC for each piston and carefully pushed the piston home insuring that it didn't touch the bore or catch on the journal. Once the bearing was sitting on it's journal the two pieces of protective rubber tube were removed from the rod bolts.

Don't forget to fit the bearing into it's cap and lubricate with assembly lube.

Last job is to torque down the rod bolts, don't forget to clean the threads first and re-oil with fresh clean oil as to manufactures specifications before torquing down.

Finally the pistons are were they belong...

Pete

PSH · Aug 15, 2012

evening all Sorry for lack of update of late, I was away for a few days break in Wales, that's twice now that I've been to Wales without my 944T, God do I miss driving my car while in places like Wales. I told SWMBO that I won't go away again unless I have my car back on the road..... well it was worth a try...

Ok so back to work.... Oil Pump I had originally intended to replace the oil pump for a new one but on reading into this it seems that the 944 oil pump rarely fails, so considering this fact, plus the fact that the oil gauge was still reading 3-4 bar on idle and 5 bar while driving ( these figures are while hot, gauge always read 5 bar at any rpm while cold) the pump is going to be kept after stripping down. First picture shows the pump casing after being cleaned up of muck and old loctite 574 sealant, note the small gouge on the inner service, the cause of this was tracked down to a burr on the outer gear cog. Not sure if this had been there since new or down to a small piece of the iridium plug that broke up some years back, all that's important to me is that the pump performed as good as new and the internals all look good as new, except the small burr mentioned that has now been filed flat.

Second picture shows the internals of the pump, the drive gear to the right is a serviceable item which you replace if it has a groove worn around it due to contact with the front oil seal. There is the slightest of marks on mine, probably due to it being replaced some years ago by a specialist so I won't be changing this, unlike the two balance shaft top hats that look original, are badly grooved and therefore will be replaced.

Next shows the internals reassembled, the gears are first lubricated with engine oil (I use Mobile 1 15/50W Motorsport), note that the outer gear has two punch marks, these must be facing to the top as shown here. This unit is held in place by the two countersunk bolts seen in the picture, the outer casing must be coated with loctite 574 before refitting to the pump housing.

Last picture for tonight shows the oil pump refitted to the engine block, make sure that the two outer pump flanges line up with the bottom of the block so the the sump will seal properly, the drive gear has also been refitted with a new front oil seal. The oil pump housing is sealed to the block with loctite 574 which is why it's important when fitting the main bearing frame to get it flush with the front of the engine, any ridge can be removed with a suitable oil stone but get it as flush as you can first. Pump bolts have been torqued down to Porsche spec.

next will be to refit the oil feed pipes and sump, hope to do that tomorrow. Pete

PSH · Aug 16, 2012

I didn't get as much done as planned today but will show what little I did do. Here's the oil feed pipe refitted to the main bearing frame, this took a little longer than planned as I had to remove the scraper first. In the picture I placed for reference the old seal for those who may do this in the future , this seal fits between the frame and pipe flange, it starts life as a plain flat sided seal that then deforms causing a lip as you can see on the old seal. Although the old seal looks ok it is well past it's best being rubber and 26 years old, all that heat has caused it to shrink and therefore was no longer sealing properly.

next picture is just to show ( for those not familiar with the 944 engine) the sump gasket in place awaiting refitting of the sump, silicone sealant will also be used where there are joins , for example the front flange for the oil pump. I haven't fitted the sump yet as I haven't finished cleaning up the 6mm bolts yet, should be on tomorrow.

Pete

PSH · Aug 17, 2012

Just to finish off from yesterday the sump is now back in place, Porsche torquing sequence is to install bolts, torque to 3lb's and then finally 6lb's. This is fine but a tip is to go over the sequence a number of times until all of the bolts do read 6lb. Due to the gasket being large and rubber with alloy inserts you'll find that as you go around bolts that felt tight before have loosened as others are tightened. this happens on most gaskets like this until fully compressed but for some reason it seems to be more so on the 944, so check a little more than usual.

Once I have some help here I'll turn the block over and start refitting the side components, oh and I still need to replace the rear pilot bearing and fit a new rear crank seal. Pete edit: forgot to mention the high temp silicone used on the corners of the sump, I also put some around the arched sections although it's not in the manual, it has worked for me in the past so I'll continue to do so.

944 man · Aug 17, 2012

When I look at this (and most of Ollis updates), a little bit of wee comes out. [

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PSH · Aug 17, 2012

er.. thanks Simon... hope the stain comes out...

On to the rear crank seal, first picture is just for reference to show the recess for the rear crank seal. This of course needs to be very clean before fitting the seal.

On reading various articles on the web it seems that there are two main companies who do this seal Kaco (black in colour) and Victor Reinz ( red/brown), according to what I've read the black seal is prone to leaking, lucky for me then that I have the other..

It seems that most ( state side) use Curil T to help seal the outside of the seal against the block, others fit dry while some use grease. Since Curil T is basically a high temp oil resistant silicone I've used a similar alternative available here, I also read that if the main bearing frame has been seperated it's not advisable to fit dry, hence why I choose to use a sealant. You also need to lubricate the inner seal with either a very thick oil or assembly lube so as to stop the seal burning out to give the engine oil time to fully reach the seal when first run.

There are a number of ways to fit the seal, the proper tool if you have it, if not you can either use a suitable sized piece of PVC pipe or a piece of wood, all need a tap with a hammer to force the seal home. I chose to use a piece of wood, first gently pushing the seal in square and then tapping very carefully at opposite sides until the seasl was half way in as shown here.

Finish with small gentle taps around the circumference until fully seated and wipe clean

Last picture has the engine returned upright, it's beginning to get heavy again..

As mentioned previously I am going to replace the balance shaft top hats which is why one side is still not fitted, the other I will have to take off and redo. Now that the engine is back up the right way I can start to fit the various engine mount supports, oil housing,water pump etc etc.. the list goes on, hope I can remember where it all goes...

Pete

MarkK · Aug 17, 2012

PSH · Aug 21, 2012

Engine mounts back on, right hand side first

and now the left hand side which also incorporates the Turbo support mounting, I have replaced the turbo oil seals and the black elbow hose seen in the picture will be replaced by a nice new shiny PSH silicon hose to match the others later.

Pete