-
290psi on Franken Engine??? Too Low?
by
barrygti
on 28 Jul, 2009 22:07
-
Right my Franken engine has been terrible to start from day one when cold, all glow plugs checked, timing played with over and over but still the same. Crap to start when around zero celsius in mornings and misses slightly at first but starts better when warm and runs perfect once running.
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I measured protrusion for gasket thickness etc so I am sure it's not that, do we think a hone and a set of rings will sort it?
-
#1
by
arb
on 29 Jul, 2009 05:06
-
Right my Franken engine has been terrible to start from day one when cold, all glow plugs checked, timing played with over and over but still the same. Crap to start when around zero celsius in mornings and misses slightly at first but starts better when warm and runs perfect once running.
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I measured protrusion for gasket thickness etc so I am sure it's not that, do we think a hone and a set of rings will sort it?
Wow, surprising it starts cold. Your starter must be in great condition and you must have synthetic oil so it spins faster... I'd want to see over 400 psi per jug. You're 25% or more below.
-
#2
by
Mark(The Miser)UK
on 29 Jul, 2009 08:07
-
Right my Franken engine has been terrible to start from day one when cold, all glow plugs checked, timing played with over and over but still the same. Crap to start when around zero celsius in mornings and misses slightly at first but starts better when warm and runs perfect once running.
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I measured protrusion for gasket thickness etc so I am sure it's not that, do we think a hone and a set of rings will sort it?
Wow, surprising it starts cold. Your starter must be in great condition and you must have synthetic oil so it spins faster... I'd want to see over 400 psi per jug. You're 25% or more below.
Be sure that your compresion tester is not lying to you. If compression very low, then surely blowby would be high, and you would be using a lot of oil and perhaps blue smoke too...
My Snap-On has a home made injector body adaptor stuffed with lead, and it needs further mods because the last reading I took for a cylinder only read 250psi
... However I may have touched 50mpg US on a journey I just returned from.
-
#3
by
arb
on 29 Jul, 2009 08:13
-
Right my Franken engine has been terrible to start from day one when cold, all glow plugs checked, timing played with over and over but still the same. Crap to start when around zero celsius in mornings and misses slightly at first but starts better when warm and runs perfect once running.
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I measured protrusion for gasket thickness etc so I am sure it's not that, do we think a hone and a set of rings will sort it?
Wow, surprising it starts cold. Your starter must be in great condition and you must have synthetic oil so it spins faster... I'd want to see over 400 psi per jug. You're 25% or more below.
Be sure that your compresion tester is not lying to you. If compression very low, then surely blowby would be high, and you would be using a lot of oil and perhaps blue smoke too...
My Snap-On has a home made injector body adaptor stuffed with lead, and it needs further mods because the last reading I took for a cylinder only read 250psi ... However I may have touched 50mpg US on a journey I just returned from.
Excessive blow by only if it is rings. It could also be bad valve seats - how many miles are on the head ? If they are not sealing properly, your low compression could be going out the valves rather than the rings.
You could do a pressure test - pull the GP, attach an air fitting to the head (I don't have such a fitting, but would make one out of a bad GP if I needed to) and connect to shop air (being careful that cylinder is near BDC and not TDC) If the valves are leaking you'll hear the air in the intake / exhaust manifold. If its the rings, you'll hear it in the crank case (Mechanic's stethoscope helps). Could be both...
-
#4
by
barrygti
on 29 Jul, 2009 11:53
-
Yes next step is cylinder leakage test. Head was stripped right down, skimmed, crack tested, valves lapped in and spring rates and lifters tested. Has done 1000 miles since then but always had starting issue.
-
#5
by
burn_your_money
on 29 Jul, 2009 15:20
-
Don't you need to do the pressure test at TDC so both valves are closed?
My 1.6 NA that had around the same compression didn't have excessive blowby. It ended up that all my cylinder walls were scored pretty good.
-
#6
by
jtanguay
on 29 Jul, 2009 16:40
-
hone & set of rings will get you by for a little while... running an oil stabilizer like lucas might help too... but it would be a good idea to get the head checked out while you have it off.
-
#7
by
rabbid79
on 29 Jul, 2009 21:33
-
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I'm curious why the engine's naturally lower compression ratio due to large combustion/swirl chambers isn't really the primary suspect. To me, all indications are that it's the naturally low static compression ratio contributing to poor starting. I would look there first, and try to find a suitable way to start a low compression ratio engine, such as coil to heat up intake air (as is used on Cummins), or super fast cranking speeds (maybe run 24V to your starter).
-
#8
by
Vincent Waldon
on 29 Jul, 2009 22:48
-
I'm curious why the engine's naturally lower compression ratio due to large combustion/swirl chambers isn't really the primary suspect.
Hmmm... the IDI has 23:1 compression... actually higher than the TDI design (17:1)...so I must be misunderstanding your point?
-
#9
by
barrygti
on 30 Jul, 2009 00:13
-
I do have to say that the cylinder bores were perfect when apart 1000 miles ago no scoring and almost NO side to side piston movement. I never pulled a piston though obviously.
I know running the 1.9 head means lower compression but I researched it lots(franken engine)before doing it and no one mentioned hard starting due to the compression drop? I wouldn't assume it would lower the compession so much that it would cause this.
Last thing I want to check is wether air is somehow getting in to diesel supply, I don't have a clear hose on it so might do that next.
-
#10
by
rabbid79
on 30 Jul, 2009 00:29
-
He's talking about the fact that the AAZ cylinder head has larger pre-chambers than the 1.6 and so using the AAZ head on the 1.6 will result in naturally lower compression.
Andrew's right, that's exactly what I'm talking about.
Last thing I want to check is wether air is somehow getting in to diesel supply
That sounds like a good next step. Just for kicks, try directing some hot hair from a heat gun or hair dryer into your intake when you try starting it, as this might be a good alternate means of getting it going on the really bad days. During startup, the more heat you can get into that engine the better. Have you tried a block heater? Total Seal rings might be a good way to go if they can improve the compression.
I think we have a vested interest in your starting problem since a lot of us are interested in Franken engines, and want to know what kinds of problems there might be.
-
#11
by
barrygti
on 30 Jul, 2009 00:36
-
Good idea on the hot air gun, will try that on Saturday morning. I don't have a block heater as they are not readily available here in New Zealand and cost a fortune where you can find them.
I am interested in the idea of an intake air heater like Cummins, will look in to that.
I did try and look at ways of making my starter gruntier, I have a HUGE battery in there but other than converting EVERYTHING to 24v(no chance) I am not sure of anything else I could do.
Will get some pictures done at weekend too I think
-
#12
by
saurkraut
on 30 Jul, 2009 10:06
-
Right my Franken engine has been terrible to start from day one when cold, all glow plugs checked, timing played with over and over but still the same. Crap to start when around zero celsius in mornings and misses slightly at first but starts better when warm and runs perfect once running.
Today I done a compression test and was between 285 and 295psi on all Cyls, was a cold test, started car pulled it in to workshop and then done test. From what I read this is too low??
I measured protrusion for gasket thickness etc so I am sure it's not that, do we think a hone and a set of rings will sort it?
From some calculations I made a few years ago, when you put a 1.9 head on a 1.6 block, the compression ratio drops to 19:1. I don't know what the cranking pressure should be though. I would suspect that 400 PSI is out of the question, and you may be seeing what this engine/head combination is capable of.
Does any one know what the cranking pressure is of a TDi motor? If its lower than what you have, that would confirm that everything is OK, and you'll have to live with it.
One thing you could try is to run another big diameter ground wire from the negative battery terminal to one of the bellhousing bolts. The stock grounding set up is less than ideal.
The 1.5L diesel white paper (in the FAQ section) goes into the selection of the 23.5:1 compression ratio as a balance between cold start performance, and cranking losses from excessive compression.
-
#13
by
barrygti
on 30 Jul, 2009 12:12
-
This is in a Skoda pickup not a Golf. Earth wiring is all very good, and starter turns over great. I wonder what the compression is on a Franken then....... hmmm
-
#14
by
burn_your_money
on 30 Jul, 2009 15:50
-
What do you have your pump timed to?