Jump to content
Impact Bumpers
MaxDiesel

Time for a top end rebuild ?

Recommended Posts

Just finished doing a cylinder leakage test and compression check on my '87 3.2 - its done 143k miles with full service history, no previous rebuild, uses about 1 litre of oil per 1500 miles (including minor leaks), doesn't smoke and runs well.

 

Here's what I got:

 

Leakage Compression

Cylinder 1: 16% 185 psi

Cylinder 2: 13% 198psi

Cylinder 3: 9% 200psi

Cylinder 4: 33% 170psi :o

Cylinder 5: 27% 175psi :huh:

Cylinder 6: 16% 188psi

 

All done with engine cold, leak check done with 100psi pressure in cylinder. The Snap-On gauge I used indicates 10 - 40% as low leakage (green), 40 - 70% as moderate (yellow) and 70 - 100% as high (red !). Cylinders 4 and 5 also hissed more than the others - when I removed the oil filler cap I could feel the air blowing out so this makes me think it's getting passed the rings and not valve seats.

 

I'm trying to decide whether to do a top end rebuild this winter - given these numbers I think my minds made up to get stuck in - only problem is it seems to be running so well at the moment and I usually stick with the "if it ain't broke" approach.

 

I'd de interested to know what leakge and compression numbers folk have got with similar age & mileage engines. I was a bit surpised how high the compression numbers were given the age and mileage.

Share this post


Link to post
Share on other sites

You are well in the rebuild zone there amigo. There are some numbers on the board, search for some of SP72's posts.

Share this post


Link to post
Share on other sites

My leak test figs were circa 23-28% across 4 cylinders IIRC, compression was 175-180 across all 6.

 

Bear in mind there's a car on here with 30+% loss on some cylinders, and still mapped by Schofield to 245 -ish bhp.

 

Couple of indies didn't think a rebuild was necessary when i approached them, as long as i was happy topping up the oil.

 

SP

Share this post


Link to post
Share on other sites
My leak test figs were circa 23-28% across 4 cylinders IIRC, compression was 175-180 across all 6.

 

Bear in mind there's a car on here with 30+% loss on some cylinders, and still mapped by Schofield to 245 -ish bhp.

 

Couple of indies didn't think a rebuild was necessary when i approached them, as long as i was happy topping up the oil.

 

SP

 

Thanks - sounds like mine's in similar condition to yours pre rebuild. I've rebuilt a couple of 4 cylinder Porsche Super 90 engines before and always wanted to do a flat six engine, so it looks like I'm about to get the opportunity (ordered Wayne Dempsey's How to Rebuild 911 engines earlier this evening !).

 

Just been reading the posts on your rebuild - great job and nice spec, I'd been thinking I might go the 3.4l route when the time comes. Have you had yours on a dyno since the rebuild ?

Share this post


Link to post
Share on other sites
Thanks - sounds like mine's in similar condition to yours pre rebuild. I've rebuilt a couple of 4 cylinder Porsche Super 90 engines before and always wanted to do a flat six engine, so it looks like I'm about to get the opportunity (ordered Wayne Dempsey's How to Rebuild 911 engines earlier this evening !).

 

Just been reading the posts on your rebuild - great job and nice spec, I'd been thinking I might go the 3.4l route when the time comes. Have you had yours on a dyno since the rebuild ?

not yet, currently at Jaz for its 1000 mile post rebuild service - if i can get hold of Wayne Schofield, will get it mapped too. Feels great at present, with a strong surge from 3k to 6.5k.

 

if you can factor in a twin plug solution (which i couldn't stretch to), you may want to consider going for 100mm P&C's for a 3.5 conversion using Nickies.

 

SP

Share this post


Link to post
Share on other sites

It was a similar test that prompted me to rebuild my motor. I had between 20% and 45% losses. It seemed to be running OK before, it wasnt until a dyno/mapping session that I found out the problem.

 

Sounds like you are egging for the challenge, so good luck fella.

Share this post


Link to post
Share on other sites

I had thought that a leakdown test should be done hot rather than than cold. That said, your leakdown values and compressions (to a lessor extent) show quite a lot of variance across cylinders.

 

David

Share this post


Link to post
Share on other sites
I had thought that a leakdown test should be done hot rather than than cold. That said, your leakdown values and compressions (to a lessor extent) show quite a lot of variance across cylinders.

 

David

Yes, agree the leakdown test would be more representative on a hot engine - the rubbish weather stopped me from taking it for a warm up run today....( also a lot easier to do when the engine's cold ! ). As you say the compression numbers and leakage rates indicate the same trend so I think they provide a pretty good indication.

Share this post


Link to post
Share on other sites
It was a similar test that prompted me to rebuild my motor. I had between 20% and 45% losses. It seemed to be running OK before, it wasnt until a dyno/mapping session that I found out the problem.

Aiming to get the car on a chassis dyno at work one evening this week to see how its really performing - what peak power & torque numbers were you getting with 20 - 45% losses ?

Share this post


Link to post
Share on other sites
Aiming to get the car on a chassis dyno at work one evening this week to see how its really performing - what peak power & torque numbers were you getting with 20 - 45% losses ?

Got my car on the chassis dyno tonight - must admit its quite nerve racking keeping your right foot nailed to the floor all the way into the red when its your own car ! Haven't processed the data yet but max power recorded at the wheels was just over 180hp, not bad for a 20+ year old car with stock engine and >140K miles on the clock. Will post some graphs tomorrow night.

Share this post


Link to post
Share on other sites
Got my car on the chassis dyno tonight - must admit its quite nerve racking keeping your right foot nailed to the floor all the way into the red when its your own car !

It's not that hard ;)

 

th_BrandsGP_April_7k_rev.jpg

Share this post


Link to post
Share on other sites

Had a chance to look at the data from my runs on the dyno last night. All figures are vehicle power & torque measured at the wheels:

powercurvekWNm.jpg

 

For those who prefer hp and lbs ft:

 

powercurvehpandlbsft.jpg

 

Looking at the torque curve I guess its no surprise it feels a little flat below 4000 rev/min - I was surprised to see peak torque isn't until 5000rev/min - this is something I'll have to work on during the rebuild !

 

Going to use these as a baseline pre top-end rebuild - will be interesting to see how it compares post rebuild and a few minor upgrades...

 

Nice new high-lift jack arrives tomorrow, tax disc runs out Friday - so the fun will begin soon !

Share this post


Link to post
Share on other sites

So decision made to go for a top end rebuild this winter. Got to use my new high lift Sealey jack in anger yesterday - worked a treat, lifted the car to give 33" ground clearance at the back end and was only about 2/3 of its max height. Only trouble then was I had to stand on a box to reach in the engine bay...

 

DSC00003.jpg

DSC00001.jpg

 

Followed the engine removal checklist in 101 Projects your Porsche - all went fine apart from one important step it misses out for G50 models. After an half an hour of heaving at the engine and only moving it about 10mm from the transmission I realised it was being held in by the clutch release fork. Time to check the Bentley manual which clearly says to remove the clutch cross shaft with slide hammer before splitting engine and trans. So next step was to weld a 6mm bolt to a length of 10mm stud to make a crude slide hammer - worked a treat.

 

DSC00033.jpg

 

Engine came out easily once the clutch cross shaft was out. I found keeping the engine steady on the jack a hell of a lot harder than my old 912 engine and many Beetle engines I've done. Had to enlist the wife to operate the jack while I steadied the engine, was relieved to get it down on the ground.

 

DSC00065.jpg

 

Have removed clutch and flywheel ready to get it up on the engine stand, debating whether its really necessary to use a proper Porsche yoke rather than the universal adapter. If anyone down in the South has a Porsche adapter that they'd be willing to loan me for a couple of months please shout.

Share this post


Link to post
Share on other sites
debating whether its really necessary to use a proper Porsche yoke rather than the universal adapter.

 

I would not put my engine on a universal adaptor.

Share this post


Link to post
Share on other sites
I would not put my engine on a universal adaptor.

...but plenty of other people do.

 

Same high lift jack I have. Never use it on uneven ground :whistling:

 

Good work on the engine removal, and the sickeningly tidy garage! ;).

Share this post


Link to post
Share on other sites
I would not put my engine on a universal adaptor.

 

 

...but plenty of other people do.

 

That does not mean it is a good idea

Share this post


Link to post
Share on other sites
Quite. You a surgeon in your spare time MD?

 

Just a frustrated engineer.... I don't get hands-on at work anymore so I spend too much time in my garage !

Share this post


Link to post
Share on other sites

:signs118:

I'm doing my top end at the moment, wish my garage was as tidy.

I'm using a std yoke set up " OK as I'm not splitting the cases" did have to extend the shaft though to miss the exchangers on 360 deg rotation.

 

Get plenty of boxes " then some more"

 

arrow.jpg

PICT0137.jpg

Edited by coxy

Share this post


Link to post
Share on other sites
I'm doing my top end at the moment, wish my garage was as tidy.

I think the level of tidiness will go down hill rapidly as soon as I start taking the engine apart !

 

I'm using a std yoke set up " OK as I'm not splitting the cases" did have to extend the shaft though to miss the exchangers on 360 deg rotation.

 

Also not intending to split my cases (unless I find something horrible...) so I'm inclined to go with the universal adapter like yourself. Good point on clearing the heat exchangers - I hadn't considered this at all. How did you extend the shaft - just by welding an extra length of tube on ?

 

Just seen your post on tinware - if you find a supplier for the rear piece that includes the shield over the cross-over pipe please let me know - I've already had a go a mine with the welder once before and I think its beyond recovery this time !

Share this post


Link to post
Share on other sites
Also not intending to split my cases (unless I find something horrible...) so I'm inclined to go with the universal adapter like yourself. Good point on clearing the heat exchangers - I hadn't considered this at all. How did you extend the shaft - just by welding an extra length of tube on ?

 

Just seen your post on tinware - if you find a supplier for the rear piece that includes the shield over the cross-over pipe please let me know - I've already had a go a mine with the welder once before and I think its beyond recovery this time !

Its just a 60mm tube welded on to the existing shaft then replicate the holes (plenty strong enough) before anyone asks. Also needed to alter the adjustable bars a little " by drilling an extra hole in two of them. Cost me £10 to alter rather than £xxx on a porsche adaptor.

 

Ive tried everywhere for tin "rocking horse" comes to mind. may have to make new.

 

Don't like parting with my hard earned if i don't have to, so i got the welder out this weekend. Worked a treat.

 

PICT0092.jpg

PICT0095.jpg

Share this post


Link to post
Share on other sites

Progress update (been a bit slow as v. busy at work...)

Got my engine stripped down to a long block assembly now:

DSC00113.jpg

Time for a de-grease and pressure wash:

DSC00117-1.jpg

 

DSC00122.jpg

Also stripped the fan / alternator assembly, removed steel hub and modified for stainless fastners:

DSC00108.jpg

All ready to be plated or powder coated - waiting for my local plating specialist to come back to me on what he can do with magnesium:

DSC00106.jpg

Inlet manifold and fuel system strip underway:

DSC00093.jpg

Nearly finished making an engine stand adapter at work, have had the ring turned - just got to halve it and machine the fixing points now. Hopefully have my engine on the stand next weekend.

Share this post


Link to post
Share on other sites

Finished making my engine stand adapter at last - turned out to be a bit more effort than I first thought (like most projects !):

DSC00156.jpg

Started by measuring the engine and stud locations several times, then did some old fashion drawing. Flame cut the ring from 1" steel plate and then turned the main diameters and spigot diameter. Machined M12 threads for the engine stand, clearance holes for the engine studs and 45 degree cut back to clear the oil cooler. Finally stress relieved the ring before band sawing it in half - beauty of it is I've ended up with two adapters !

DSC00138.jpg

Fits on either side of the engine fine:

DSC00139.jpg

DSC00142.jpg

Bolted up to the engine stand adapter:

DSC00146.jpg

And now on the engine:

DSC00154.jpg

Ideally need to turn a couple of spacers to replace the assorted nuts etc. I'm using on the engine studs. Will be enlisting some help from friends in the morning to get the engine up on the stand. Can then start getting the rest of the engine apart at last.

 

If someone's interested in the second adapter please get in touch - it owes me a fair bit in materials and beer tokens used up at work so I'll need to ask a fair price for it - will be a lot less than the equivalent on Pelican though.

Share this post


Link to post
Share on other sites
If someone's interested in the second adapter please get in touch - it owes me a fair bit in materials and beer tokens used up at work so I'll need to ask a fair price for it - will be a lot less than the equivalent on Pelican though.

Beautiful work and well done mate, PM me with the price ;)

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.

×
×
  • Create New...