Head gasket replacement - lower than expected compression
Discussion
I've spent 12 of the last 16 weekends doing an engine swap on my Peugeot 106 Rallye 8v - > 16v.
Multiple reasons for this, not least of which I bought a pup ( it was very local) and I cocked up the replacement of the front crank seal, which necessitated taking the engine back out.
This weekend I discovered I needed to replace the head gasket. (failed sniff test and, sludgy oil / coolant/ 1 cylinder low comp ). I fitted a 1.5mm 4 piece MLS head gasket that was specced as correct for the car. However upon checking the compressions, (whilst they are now all within about 3psi) they are 180 hot,(they were about 150 cold) when I was expecting 200-220. Indeed apart from one cylinder being down to 167, previously the compressions were 195-205.
I did not skim the head, it was checked and no issues were found (e.g warping, or non flat surface). So I cleaned both head and block surfaces and put the engine back together.
180psi is going to cost me about 6 hp.
I can't find a thinner head gasket than 1.37mm. So is it the case that I need to skim the head to get the compression back I was expecting? I am guessing around 0.060 would need to be removed.
Unless someone knows the part number for a 1mm head gasket - which is what came off the car?
Oh and I should also ask - where do you find the proper tool/socket to tighten the head bolts (inverted hex) . 11 mm socket works but I can't help thinking there is a proper head bolt torquing tool.
Multiple reasons for this, not least of which I bought a pup ( it was very local) and I cocked up the replacement of the front crank seal, which necessitated taking the engine back out.
This weekend I discovered I needed to replace the head gasket. (failed sniff test and, sludgy oil / coolant/ 1 cylinder low comp ). I fitted a 1.5mm 4 piece MLS head gasket that was specced as correct for the car. However upon checking the compressions, (whilst they are now all within about 3psi) they are 180 hot,(they were about 150 cold) when I was expecting 200-220. Indeed apart from one cylinder being down to 167, previously the compressions were 195-205.
I did not skim the head, it was checked and no issues were found (e.g warping, or non flat surface). So I cleaned both head and block surfaces and put the engine back together.
180psi is going to cost me about 6 hp.
I can't find a thinner head gasket than 1.37mm. So is it the case that I need to skim the head to get the compression back I was expecting? I am guessing around 0.060 would need to be removed.
Unless someone knows the part number for a 1mm head gasket - which is what came off the car?
Oh and I should also ask - where do you find the proper tool/socket to tighten the head bolts (inverted hex) . 11 mm socket works but I can't help thinking there is a proper head bolt torquing tool.
Edited by Dynion Araf Uchaf on Tuesday 20th September 13:46
So you're saying you fitted a thicker head gasket than before ? Seems unclear what was fitted, compared to what is now fitted.
If it is thicker, then yes of course you will need to skim the head to restore compression, if the head has enough material to skim ok.
And what do you mean by an "inverted hex" ? An Allen key ?
And you mean something like this ? ( although says out of stock )
https://marmotorsport.com/shop/race-head-gasket-1-...
If you ended up with a thicker gasket, did you just buy parts at random, or did you actually speak to some sort of 106 parts supplier who would be familiar with options ?
Has the engine actually been properly tuned and optimised to worry whether it might lose your alleged 6hp or not ?
If it is thicker, then yes of course you will need to skim the head to restore compression, if the head has enough material to skim ok.
And what do you mean by an "inverted hex" ? An Allen key ?
And you mean something like this ? ( although says out of stock )
https://marmotorsport.com/shop/race-head-gasket-1-...
If you ended up with a thicker gasket, did you just buy parts at random, or did you actually speak to some sort of 106 parts supplier who would be familiar with options ?
Has the engine actually been properly tuned and optimised to worry whether it might lose your alleged 6hp or not ?
stevieturbo said:
So you're saying you fitted a thicker head gasket than before ? Seems unclear what was fitted, compared to what is now fitted.
If it is thicker, then yes of course you will need to skim the head to restore compression, if the head has enough material to skim ok.
And what do you mean by an "inverted hex" ? An Allen key ?
And you mean something like this ? ( although says out of stock )
https://marmotorsport.com/shop/race-head-gasket-1-...
If you ended up with a thicker gasket, did you just buy parts at random, or did you actually speak to some sort of 106 parts supplier who would be familiar with options ?
Has the engine actually been properly tuned and optimised to worry whether it might lose your alleged 6hp or not ?
I measured the one I took out the car and it was 1mm.If it is thicker, then yes of course you will need to skim the head to restore compression, if the head has enough material to skim ok.
And what do you mean by an "inverted hex" ? An Allen key ?
And you mean something like this ? ( although says out of stock )
https://marmotorsport.com/shop/race-head-gasket-1-...
If you ended up with a thicker gasket, did you just buy parts at random, or did you actually speak to some sort of 106 parts supplier who would be familiar with options ?
Has the engine actually been properly tuned and optimised to worry whether it might lose your alleged 6hp or not ?
The one I put in was 1.5mm - and I spoke to ECP who said it would fit.
The head has not been touched - it's the first time the engine has been apart, so I would imagine that there is plenty of material to remove.
It's a race engine, but only because it is in a race car. Standard cams, timing, injectors etc. Although mappable ECU ( and it has been mapped). Bottom end has done probs 100k miles. So it's not a custom built special in any way really.
I read somewhere that each point of compression lost is about 3% of overall power. 14.1 to 10.1
Head bolts look like this
The sockets are star....not hex. Regular sockets etc are hex.
https://www.amazon.co.uk/Female-Socket-E4-E24-Exte...
Really, if it's together and running well....just carry on and don't worry about it
if you really want to have the same as before, then take it apart and fit a head gasket the same thickness as before.
https://www.amazon.co.uk/Female-Socket-E4-E24-Exte...
Really, if it's together and running well....just carry on and don't worry about it
if you really want to have the same as before, then take it apart and fit a head gasket the same thickness as before.
DVandrews said:
incorrect cam timing being the main one.
Dave
Is a interesting call!!!!Dave
Perhaps If the inlet/exhaust cam timing is out you may not be getting a fully seated valve at what should be tdc and getting iffy compression test results.
check the cam timing marks again to rule it out. Its been a few years since i had a Xsara VTR with a slightly less tuned 106GTI engine in, im fairly sure there a special tool for locking the cams on the TU engines which i didn't have when I did a belt change which made things more awkward than it should have been and I'd not removed the head or moved anything!
Also, not a dig as I learnt the hard way wasting time rebuilding a golf gtI engine twice within a few hundred miles. Any time a head is off a block it is barely £100 to get a machine shop to clean, pressure test and skim it. Plus an opportunity to have valve stems seals done, it saves so much grief in the future and is often cheaper than a new head gasket kit, bolts & consumables as you may (sadly) be about to find out.
I have the cam locking tool I used it to change the belt. I did lock the cams in place however I may have moved them at some point during the cleaning as they weren’t 100% lined up on reassembly. It was a fairly easy fix as the cam wheels are adjustable. So adjusted them as per photos I took before I even touched the engine.
I took a look at the valves along with an engineer friend of mine and we both concluded that they were fine. You could go to town and lap them in but not for a performance gain. One set of stems seals is knackered however, but that doesn’t explain the drop in compression.
I had 3 days to to the HG change ( not something I’ve done before) so it had to be fixed by the end of the weekend so couldn’t send the head off . Once I’ve raced the car I’ll take a view about what to do next but on the list will be new gasket, and a cylinder head refurb.
At the end of the day it’s an eBay engine standing me at £0 , i had to fix the numerous oil leaks but I am not rebuilding it until I can race it to see what I’ve got.
Just to add a level of excitement. I’ve just realised I did the comp test with the throttle closed! In addition to that there is not cold start map on the engine as my ecu does not have that. So my mapper used liquid metal to block up the gaps In the TB. Therefore the two things combined probably means there was less air in the cylinder to compress. Possibly.
I took a look at the valves along with an engineer friend of mine and we both concluded that they were fine. You could go to town and lap them in but not for a performance gain. One set of stems seals is knackered however, but that doesn’t explain the drop in compression.
I had 3 days to to the HG change ( not something I’ve done before) so it had to be fixed by the end of the weekend so couldn’t send the head off . Once I’ve raced the car I’ll take a view about what to do next but on the list will be new gasket, and a cylinder head refurb.
At the end of the day it’s an eBay engine standing me at £0 , i had to fix the numerous oil leaks but I am not rebuilding it until I can race it to see what I’ve got.
Just to add a level of excitement. I’ve just realised I did the comp test with the throttle closed! In addition to that there is not cold start map on the engine as my ecu does not have that. So my mapper used liquid metal to block up the gaps In the TB. Therefore the two things combined probably means there was less air in the cylinder to compress. Possibly.
Edited by Dynion Araf Uchaf on Tuesday 20th September 20:19
Dynion Araf Uchaf said:
I have the cam locking tool I used it to change the belt.
I had 3 days to to the HG change ( not something I’ve done before) so it had to be fixed by the end of the weekend so couldn’t send the head off . Once I’ve raced the car I’ll take a view about what to do next but on the list will be new gasket, and a cylinder head refurb.
At the end of the day it’s an eBay engine standing me at £0 , i had to fix the numerous oil leaks but I am not rebuilding it until I can race it to see what I’ve got.
Fair play for getting stuck in and having a go, I've faced similar predicaments in the past when you need a car fixed yet can't take your time and do all the "whilst I'm here" jobs you'd like to get done then find yourself redoing plenty of the same work not long after. Dam learning curves..I had 3 days to to the HG change ( not something I’ve done before) so it had to be fixed by the end of the weekend so couldn’t send the head off . Once I’ve raced the car I’ll take a view about what to do next but on the list will be new gasket, and a cylinder head refurb.
At the end of the day it’s an eBay engine standing me at £0 , i had to fix the numerous oil leaks but I am not rebuilding it until I can race it to see what I’ve got.
Good luck @ racing!!
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