Evening everyone, got a problem I need advise on. Bit of info first. Type 4 engine 1700 W code Total rebuild Used 2.0lt heads to replace 1.7 heads with appropriate barrels and pistons for the 2.0lt heads Every step of the way I have checked that everything is moving freely. Put one B+P on, checked all is good. Put second B+P on, checked all is good... etc. You get the picture. check check check. My problem is, everything torqued up properly and everything moving a treat, until i install the rocker arm assemblies in the heads. Engine will not turn with rockers installed. The rockers sit nice and square when located on the lugs but as soon as i tighten up I can not turn over engine. The rockers arms can be moved up and down by hand but not by the push rods when torqued up. But push rods move up and down great without rocker assemblies. The other thing that happens with rockers installed and binding, as you try to turn engine over, the crankshaft moves in the case. Pushes out fan end. They are 2.0lt rockers that were with the heads Have I cocked up somewhere or are my rockers assemblies to blame. Any engine builder come across this thing before? Any and all help please, really need to get the engine running in my bus. It's been a two year build on the engine and 6 years on the bus. So, so close. HELP......
So, you have a 1700 crank with 2.0l barrels and pistons? What rods did you use? What deck height and CR do you have. What cam have you used? Are you sure the push rods are located properly in the cam followers and the rockers? 1700 rockers are different to 2.0l but the ratio is the same (1.3:1) and I doubt if the rockers are the problem. You’re presumably turning the engine without the flywheel so the end float has not been set and the crank is probably jamming inside the crankcase.
Ours was like that after I rebuilt it... I even took it right back to pots off and back together.. still well stiff.... have ago at turning with plugs out then try again making sure timing is right... but it is quite hard to turn over by hand. She runs great though, mostly, so perhaps that's how hard it is! And put a fly wheel on to set end float.. just in case.. Sent from my SM-G930F using Tapatalk
What about pushrod length? Is there such an issue.. I say this because, when we built our type 4 motor, we found some pushrod tubes too short and didn't seat correctly which has no connection to pushrod length..but if they have been made too long.
Yep, 1700 crank and rods with 2.0 l heads. B+P are 96x66 kit. 1700 up to 1911cc. Cam is scat C25. Push rods snug in solid followers and rockers. Rocker assemblies are from 2.0l heads. Can't remember deck height but know they are within the range according to Tom Wilsons book. Dumb question, but whats CR? No flywheel on yet. Thanks for answering No plugs in, nice air compression coming out of plug holes before i install rockers. yep been back to B+P off twice to double check, again. Thanks for answering.
Will have to check length when next with engine. Got a feeling they are your standard 2.0l tubes and push rods thanks
Another thought. When you build the rocker assemblies up, what happens if you build up #1 cylinder and rotate the motor (with #'s 2, 3 and 4 with no pushrods and rockers), does that stop the motor turning? If not, move on to #2 cylinder and do the same, and so on, to see if its localised to one cylinder.
If you can get it to turn with rockers on but no plugs in it could be just having good compression.. with new heads with proper sealing valves and a bit of oil in the rings squashing that air is harder than you'd think! Sent from my SM-G930F using Tapatalk
CR is compression ratio, I personally think it will be difficult to turn over the engine with all new stuff without a fly wheel, how are you turning it over?
Good idea, will give this ago. Cylinder #4 in the barrel seemed stiffer than the other three when I was connecting pistons to rods and sliding up and down the barrels to seat. Ta Thank you, it had crossed my mind and I may be over worrying. First build. The heads have all new guides and valves, barrels+pistons so maybe once rockers are installed, MEGA compression. I will put flywheel on and set end float and see how I go. Many thanks everyone.
CR, yes sorry got it. Turning over by just the nut for the fan. Which is fine until the rockers are installed then virtually no give. I will put flywheel on and see how I get on. As I mentioned in another reply, I maybe over worrying that the engine turned over good with a spanner on the fan bolt but just stopped once rockers installed. Flywheel and end float next I think. Thank you
With a C25 cam you should have a CR of 7.5:1 to 8:1 for it to work well. If you have just used the Tom Wilson book you probably don’t know what the CR is; if it’s too low the engine loses efficiency, too high and there could be a risk of pre-ignition and piston damage. You don’t want ‘MEGA’ compression. Tom Wilson's book is good for the basics of building an engine but it’s not much use once you deviate from standard parts and specifications. The parts you have used should be fine, standard push rods will be okay but you need HD valve springs with the C25 cam. A couple of things not mentioned earlier that you need to check. Piston ring gaps and valve spring coil clearance, you need 0.060” 1.5mm between the coils at full lift. If the springs are coil bound it would cause the symptoms you have and if you force it you risk bending the pushrods. Don’t continue to build the engine if you feel it tightening up too much as you install the rockers, obviously it will become tighter as you start to compress the valve springs but with the plugs out you should be able to turn it over on the pulley by hand. You said ‘Engine will not turn with rockers installed. The rockers sit nice and square when located on the lugs but as soon as I tighten up, I cannot turn over engine.’ If that’s what you really meant something is wrong. Fit the flywheel (without the seal) before you do any more checks, without it there is nothing to stop the crank moving sideways and hitting the crankcase.
^^^ This might as well shim your endfloat while you are at it I wouldnt rely to much on the fan hub bolt to turn it over, if it snaps you could be in a world of pain
Thank you for the info. I will be back on the engine early next week. I will check in with you and let you know the outcome. Manythanks.
